Britbike forum

Classic British SparesKlempf British PartsBaxter CycleBritBike Sponsor SteadfastCyclesThe Bonneville ShopLowbrow CustomsGirling Classic MotorcycleLucas Classic MotorcycleHepolite PistonsIndustrial tec supply

Upgrade Your membership! Premium Membership Gold Membership Vendor Membership

New Sponsor post
2023 Classic Triumph Motorcycle Calendars
by C.B.S - 09/22/22 5:28 pm
New FAQ post
Member Spotlight
Trenton, New Jersey
Posts: 1,248
Joined: February 2007
Comment Guidelines: Do post respectful and insightful comments. Don't flame, hate, spam.
Top Posters(30 Days)
kevin 111
DavidP 68
Top Likes Received (30 Days)
reverb 29
kevin 25
Newest Members
Fritzilo, Fishbreath, Oilysock, Pacho, Abtinnmant150
12,264 Registered Users
Who's Online Now
5 members (Mike Muir, Blown Income, BeezaBryan, L.A.B., JER.Hill), 19 guests, and 20 robots.
Key: Admin, Global Mod, Mod
Forum Statistics
Most Online204
Jul 10th, 2022
Thread Like Summary
A65Matt, Big Al in York, gavin eisler, JER.Hill, kevin, konon, Mark Parker, MarksterTT, Nick H, NickL, PEH, pushrod tom, Stuart Kirk, Triless, Twin Pot Phil
Total Likes: 94
Original Post (Thread Starter)
#841500 03/01/2021 6:51 AM
by NickL
Running up after fitting new cam etc, old moron tweaking the carb........
Liked Replies
#847863 May 3rd a 03:18 AM
by Mark Parker
Mark Parker
Plenum effect is back, if I move the box around over the thing running the vacuum moves up and down, so the effect helps when it crowds the intake a little.

So through the std 40.5mm 152cfm ,about, and 157.3 through the seat opened to the 42mm valve, both with the 34mm carb. If my base calculation is correct. So a stock valve with 34mm carb should perform really well with this port and I will do a head.

I cannot do the 42mm seat properly without the proper guide fitted and K-lined which is annoying. I cut it so I could mark it with blue, but hopefully will be close. The worst thing on these is an automotive cutter to cut 3 angles at once, as the hemi insert then gets cut in with a step to get a top cut, the deeper the worse.

The plenum effect gives 171 with no carb and radiused entry. I guess the more it reads whatever it actually is the better. And it reads consistently and the comparison is good. But now is pulsing a bit. And higher lift is worse than .350" it makes more noise at .388" but doesn't flow more. so maybe the air is leaving an edge and breaking up at higher speed, and its faster but blocked by some turbulence?

Through the carbs it's at least + 45% on stock. I'll take some photos when I change it over for the other side.

These little welded manifolds are round 34mm tube squashed at the head end to be 30mm high and whatever wide the threads are helicoiled to smaller dia for these screws to fit.
[Linked Image from]

They are within 2cfm and one is better further open for some reason. One side broke into a valve spring recess frown so a patch. The SRM race springs fit shorter so a washer can protect the little patch.
3 members like this
#877707 Apr 15th a 01:44 AM
by NickL
As you can see here, we (the engineering team) take it very seriously
3 members like this
#881004 May 19th a 02:28 AM
by Mark Parker
Mark Parker
Tentatively speaking so far so good. I have a Lightning 34mm port and 42mm valve, reading around 180 with a bell. This morning it read 178cfm, so comparatively on the same calibration from the plate, the Thunderbolt port is 173.3 if everything is right. But parts are rough and I need a patch not tape over a hole. And I need a bit of floor built up. and a proper seat cut with a permanent guide. It may go more with luck but the same will do, what ever it actually is. It needs the floor, maybe no a lot, to increase speed with fill where it's doing nothing. More metal and less air around that port would be good.

With full vacs 31" - the 162cfm hole in the plate is 36"w. Std head the vacs will eat the water. Speed's maybe over 40" with a hose shoved down there. The other side has to be hacked out to match so it doesn't pull to one side. So Matt can steer it.

[Linked Image from]

Look where it's aiming, those stud holes. Haven't hit one yet, and it seems good. There is always the other one. Ported Triumphs and Harley XR750s have tubes in them. Making an alloy plate to patch pushrod side. Weird shape, if it's thick cannot pound it to shape so once on no more hacking that side. It cannot be just JBWeld because it cracks.

If it sets over night and the head stays where it is it should be good.
3 members like this
#884745 Jul 5th a 11:35 AM
by Mark Parker
Mark Parker
The thing looks brilliant.

[Linked Image from]
3 members like this
#884817 Jul 5th a 11:32 PM
by NickL
The front brakes are early BMC Mini sls running in triumph drums.
It was a fairly common thing in UK back in the day.
The rear is a later 2ls mini complete with drum.
Plenty of guys had hydraulic brakes on sidecars back in the day,
but to keep people happy we use a cable operated front master
cylinder. We are not allowed to link the brakes even though lots
of sidecars had linked brakes pre-62. We have a sidecar brake but
are not allowed to use it so it's isolated by a valve. Once again lots
of sidecars had brakes back in the day, it's just stupid aussie rules,
basically as no-one in Victoria has them, no- one else can.
We are not allowed disc brakes pre-62. Period 3 which is what the bike is.
Funny, you can run 9 + 10 stud triumph crap with 5 speed boxes etc
or any aftermarket norton and triumph engines that didn't exist pre-2000
but you can't link your brakes...... daft eh?
3 members like this
#889899 Sep 3rd a 03:51 AM
by Mark Parker
Mark Parker
Tall gearing is probably better than low. The difference between the 654 and the 734 in one video. The 734 is short shifting and maybe 2/3-3/4 throttle. The 734 just does stuff so easy, so unstrained. It also handles 100% better even in a straight line. It actually accelerates fantastic. Wish I'd had this in the 1970s. This has baffled pipes as well. The baffle things bolt in and don't seem to effect power that I can tell. It doesn't struggle to get going.

3 members like this
#890404 Sep 9th a 11:56 PM
by NickL
After some issues the result was 2nd over the two days.

All effort now will be focused on the offset 750 short stroke engine
with the 5 speed box.
3 members like this
#844911 Apr 2nd a 07:16 AM
by Twin Pot Phil
Twin Pot Phil
Nick, I have never quite understood the CRMC, 'they' want to reproduce 'of the period' racing, but allow not 'of the period' engines and modifications - like the oversize triples you detail.
I remember in the 80s having a conversation with 'an official' and when asked about thoughts I said overwhelmingly officious and overbearing, he was surprised at my statements! - only changed later when Ian Johnson (spelling!) became involved, more relaxed and friendly with common sense, better grids. Apparently has now gone back to the way it was - pot hunters throwing money at machinery.

PEH, Cadwell is fun because it is so narrow - it demands 'focus'. I remember Dave Hallam on his TZ750 outfit failing to turn right at park corner, the front hub ended up buried in the gearbox.

Oulton Park events are now limited due to newcomers and noise limits. The government refuses to grant 'grandfather rights' to circuits every time they are asked.

Chris Vincent's TT outfit was initially an A7 based engine, he later moved on to BMW engines to go faster. For mainland Open class events he used an A65 engine.
2 members like this
#848658 May 11th a 12:14 PM
by Blown Income
Blown Income
Originally Posted by pushrod tom
We are hoping to see Chris this year. I did the dyno work with him and was really amazed at the numbers we saw at only 6k. With your head it should make some serious record breaking horsepower.. PRT
PS, His bike is beautiful!
Hoping to see Tom and Mike this summer for some well over due tuning, the A65 LSR Lightning is sitting right up front starring me in the face when I enter my shop. I wouldnt be surprised if the 34mm carbs will need to be replaced with larger ones. As soon as I finish up a Victor I'm working on the Race bike is on the lift to check compression after sitting for a few yrs, change the oils and fingers crossed, fire her up.
2 members like this
#848727 May 12th a 06:55 AM
by Mark Parker
Mark Parker
Firebird's original head, stock valves and ported to 34mm PWKs.

This is interesting because I tested side by side with a stock head using the same valve, 40.5mm. I assume the stock head is 109cfm minus carb. With carb then 106.5cfm. The ported head is 155cfm through the 34mm carb and same valve. Or some where near it. 45.5% approximately more air. And importantly much faster. And in the Wallace hp calculator for hp based on flow about 45.5% more powerful. Std 106.5 works out at around 50hp. On their mildest spec Street/strip. High comp, 11 or 12-1 should put it in race motor mode and hp estimation. It would be interesting to see. 750cc brings rpm down.

The 42mm valves are about plus 50% through the 34mm carb.

This shows ports at stock valve size, stock 40.5mm valve, 42mm and 44.5mm.

[Linked Image from]

[Linked Image from]
2 members like this
#853473 Jul 11th a 08:01 AM
by NickL
Well, just got back from a chilly meeting. (for us soft Queenslanders anyway!)
3 races Saturday, 2 wins and a second.
3 races Sunday 1 win 1 3rd and one did not finish, he broke his lanyard and
the motor obviously died.
He was struggling as the motor was only the 650 and he was up against the big norton and the triumph again.
Also found the battery was flat after his 3rd finish.
Had fitted a new rear tyre which was way to big in overall diameter and it upset the bikes geometry by a mile.
Still, he is happy with the baby engine as his lap times were only 0.6sec slower than the 740.
It will make a very usable spare engine. Gearbox was spot-on too.
Would have been nice to have time to have set the carb up properly as it was fluffing at lower rpm, i think
the acc pump jets are a bit small. Seems a bit more difficult to get it right with this engine than the larger one.
State titles at Morgan Park in early September next up.
Found a dyno not too far away and are booking some time, hoo-bloody-rayyyyy finally.
2 members like this
#874428 Mar 14th a 04:27 AM
by NickL
Well it's been interesting.................................. Matt and his missus have had covid
but thankfully are over it now and ok. The chap who has been doing a lot of the machining
and welding etc for us has had a heart attack and got over that..... We have had the
massive flooding etc so it's sort of good to get back on with the old girl. We've done a new
swinging arm and rear wheel assembly allowing a 145x16 car tyre to be run, looks great but
has meant that the rear suspension had to be changed which may mean slightly heavier
springs. I have been tasked with sorting the brakes out as they were pretty crap. It has 2 mini
SLS fronts using triumph 7 inch drums, they had been machined out rather too much so
we had to modify the adjuster setup to get them to work properly. New shoes and wheel
cylinders are on and after sorting out the cable operated master cylinder it's come together
quite nicely. Just waiting for some fittings to turn up. The rear uses a 2 LS mini front but
that's all new with the complete mini drum etc mounted on the new hub, once again waiting
for some fittings as i've replaced all the pipework with AN3 gear. The sidecar has a switchable
mini brake as down south they don't allow sidecar brakes on pre-62, it also now has a proportioning
valve to stop it locking the wheel up as it used to.
Hopefully we will get to the next meeting up at Stanthorpe again 9/10 April. Haven't had a chance
to do anything on the engines so we'll just use the 740 and see how we go, i went through the gearbox
and it seemed ok back in November, we shall see....................
2 members like this
#876143 Mar 30th a 06:32 AM
by JER.Hill

I would suggest that after the welding, they probably heat treated and nitrided the crank.

my tuppence worth

2 members like this
#876313 Mar 31st a 10:33 PM
by NickL
I want to run it on a dyno to set the carb up properly anyway Mark.
This 'finger in the air' setup was too lean first up. They are lucky it
didn't nip the old thing up. It was showing signs of being very close
when i stripped it to put rings in yet it ran very well.
The other thing is doing a timing sweep to make sure we are getting
the best out of the burn. The only way you can do these things is
on a dyno really.
2 members like this
#877616 Apr 14th a 04:37 AM
by Mark Parker
Mark Parker
It's just mechanical Nick. It can be fixed. 6,500 off the line he's going to go through fuel riding like that. You should make a 'back off' sign with ''You are using too much fuel' to let Matt know to max it out. The other guy might hesitate, thinking about how much the Norton's guzzling. Or another one 'Stay out of his smoke it's going to let go."

My daughter knows how to do it, she was push bike champion at Bega High, her names on the wall in gold, 'Cymmon, Cymmon wait, we'll cross together'.
2 members like this
#878831 Apr 28th a 01:08 AM
by NickL
Once all apart the damage wasn't that bad, cases being welded up at the moment.
Good really as i had replaced all the bushes etc on this set and doing another set
and it's associated timing cover would be time consuming.
Sorting out a 4 spring clutch basket and machining that is next.
Debris hadn't circulated into the engine so that's good.
Splines etc are all good so is engine sprocket, getting the crank nitrided as it should
have been done originally really. Even a secret 5 speed box on it's way...........thanks
to John. Outrigger on crank will definitely go on as well, although it will not be easy
to do, space is limited. Discovered that we must fit air filters as dust and grit has scored
the bores considerably, honed out ok but it seems this bike must throw a lot of crap up
to the intake area and some circuits are a bit primitive as far as paddock arrangements go.
On stripping the carb again it seems that the float was just binding on on the side and
may be why the fuel level was going high. May have been bent slightly by transporting
with a low fuel level but sorted now and tests ok. Will fit a small regulator anyway as
the pump is delivering higher than the recommended pressure. Never had this problem
before and i used webers for years on my bike but one to note i suppose.
Frame mods have been done so the old girl should sit better now and steer properly again.
Outfits all tend to bend in the middle after years of use and the rear end mods we did
accented this.
End of 'War and Peace' for the moment eh? LOL.
2 members like this
#880319 May 11th a 11:19 PM
by NickL
Case is welded up and looks good.
While i'm waiting for stuff i thought i'd try the box fitting just the shafts/gears
and see what needs trimming. I need an endplate as i don't have a 71/72 type
handy but it's on it's way. The layshaft 1st needs the opening for the endplate
cut out a fair bit, maybe a mill or so but all else looks good. Matt is cutting up
an old case for me at the moment,that will make it easy to see what's going on.
The new outrigger plate is loose in the case which is a pain as we have to either
weld up the case a bit or make a new plate, those plates must be a tight fit or
they come loose, you can't take the load on the fixing screws. May use a 3 spring
clutch basket with a 4 spring Hub as it will make life easier with the centres.
Nothing insurmountable. The outrigger for the crank is sketched up and after
a discussion with Viv as to whether he agrees with it, he'll machine up the bits.
The guy is worth his weight in gold, just putting up with me is a major thing but
nothing within reason is too much trouble to machine up for us.

The spring i changed on the gearchange mechanism was the return spring, we
found a 3 turn early type which are a fair bit stronger than the 2 turn ones and
are heavier gauge. It has improved the action of the return and centring, it feels
more like a late one with the opposed spring.
2 members like this
#880497 May 14th a 12:59 AM
by NickL
Will be using an R16 open bearing for the crank outrigger, it is 1 inch id
so fits on the a10 crank. We have no alternator to mess about with.
The new 'box uses a 6005LLU as an outrigger, so as my existing plate uses
a 6204 bored out slightly, i can just press that out and the 6005 in.
The existing bearing is showing signs of wear anyway, they don't last long
in an outfit though it's been in a year or so.
The LLU types are double sealed so better than the 2RS versions.
The clutch setup requires a spacer sorting as the 4 spring flange is thicker.
I'll have to see if i can find some 3 inch diameter bronze bar. Still humming
and harring about using the 5 speed in this motor though as i just don't like
the gearchange setup. I'll see how we go time wise but unless the change is
really spot on, (which it seems to be now with the 4 speed) i won't run it.
We can wait and get it all done on the offset 750 in the late cases we have.
I would have liked to have tried the 750 barrel out but the crank's been cut
in half now so i'll have to wait until it's done.
2 members like this
#880907 May 17th a 11:18 PM
by Mark Parker
Mark Parker
So the late Thunderbolt head castings are a bit thicker than the early ones. (not thick enough) It seems more like the '71 in the bowl area on the twin carb but not quiet. The early T/bolt I have is small valve so not comparable. But I'm pretty sure the shape of the bowl is different.

Started hacking it on one side, hope I can get it good. I want it + 60% at least. frown

The seats will just go 42mm one isn't very central. The way they fit the guide is better on the earlier '70 without the recess because it has more grip on the guide.

The port roof needs to go straight and sweep down onto the valve or it can sweep down all the way (except for the valve spring area), but it cannot go down, then up, then down, because when it's going fast that wall is directing it, like a little car, if it aims down then up again it will leave the wall and air will break up. It isn't pushed against the bottom curve, but it needs to be smooth curve over, and the right volume with no ups, like a jump, or it will leave it. It can go wide around the valve and guide because it will be forced because it's blocked by the guide. And it needs turning onto the back of the valve, not across it. If it comes off the wall anywhere it will break up and eddie and block the port.
2 members like this
#881391 May 24th a 03:21 AM
by Mark Parker
Mark Parker
#2 didn't look quite the same and surprise surprise didn't flow the same by about 13cfm. It now looks the same and picked up 11. So doing the floor and then the pushrod tunnel. It's not much different but it directs the air. And it means I know what that depth and turn does. BSA did a B50 head and cut the bowl wrong, too deep, it was their best competition head at the time. And if you do not go there, you never know. You are just on a limit and think that is what it is.
2 members like this
#883209 Jun 17th a 11:14 PM
by NickL
You wouldn't want me to have a go on it Mark, you'd probably never see it again........

From what you say the new engine we are sorting at the moment should be along
the same lines, i'm really looking forward to getting on with it but we have had a few
setbacks and as you know delays all add up.
Fitting the existing/refurbed engine/gearbox tomorrow as the winter meeting is now
only 2 weeks away.
Heated the gearchange setup/timing cover in my bar b que to around 80 deg and found
what was going on. Nothing to do with the actual gearbox, it was the pawls and quadrant,
i replaced the pawl springs and dressed them a little then ground a small amount from the
granny tooth that runs on the return spring, then fitted a better stronger return spring.
The culmination of that lot is a change similar to that of a late late one, i'm now happy with it.
I'm so glad he's going to use late cases on his new
2 members like this
#884640 Jul 3rd a 11:03 PM
by NickL
A good weekend , it rained a little Saturday but not heavy, Sunday was lovely.
The handling is well sorted now, bike is steering very well we are pleased
with that. Bike still jumped out of third a few times but engine performed well,
not well enough to beat the big norton but he was on his tail at all the corners
and was pushing him, he just has a lot of straight line speed, about $8000.00
worth more than Matt's bike. All his brand new Molnar cases, crank etc are
bound to beat a 62 a65 with an a10 crank in it. I think when we get the 5 speed
box in it may be a different storey, Matt can out brake and out corner him anywhere
and the advantage of higher corner speed accompanied by better drive out will
even things up quite a lot. Anyway there were 6 races, 2nd in all of them.
2 members like this
#889887 Sep 3rd a 12:01 AM
by NickL
Well,the meeting's on Wednesday and Thursday which is rather strange but
apparently the only days they could book the circuit. Weather is not looking
great though.
The bike got run-up last Sunday and i ran it down the road and back to
quickly check the 'box. All seems good, motor is sharp and box changes well.
Gearing is quiet tall for this track, so as i was on Matt's suburban side-road i
couldn't get it up and 'on-the-boil' so it'll have to do as a test.
So, mods this time: fitted 20 thou head gasket
took 1.5mm off the pushrods (i hadn't shortened them before as i'm a lazy sod)
fitted 5 speed 'box.
fitted 3 piece oil-rings.
fitted 3 spring clutch with srm p'plate and 8 plate setup.

Had to cut out the primary cover and put a piece like a saucepan lid in
where the clutch is as the pressure plate was hitting the cover. The srm plate i
had is one of the early ones and they are quiet deep, that with the extra plates
caused the problem.
2 members like this
#841701 Mar 2nd a 10:48 PM
by NickL
No worries, i'll get Matt's wife to video it. I may even take it 'round for a few laps myself
if my wife lets me.... It's only a club weekend meet so pretty layed back. It's not as if i'm
going to try and win is it????
1 member likes this
#841586 Mar 2nd a 12:16 AM
by NickL
Sorry about the feet....................
1 member likes this
#842768 Mar 14th a 01:01 AM
by NickL
1 member likes this
#843092 Mar 16th a 08:49 AM
by NickL
The primary is used as a plenum the timed breather is blocked off.
That 3/8 pipe is the only breather, it seems to work fine. Never used
a reed on any of my race engines but all breath into the primary so
much larger expansion area.

Mallory was a great circuit, better before the silly 'bus-stop'. Had heaps of
fun there.
1 member likes this
#843105 Mar 16th a 12:40 PM
by Tridentman
Mallory was my local track-- I lived about 15 miles away in Rugby.
In my early days used to ride there with friends--the ride there was quite fast but the return ride after being inspired by the racing was pretty hairy.
My favorite spot to spectate was on the exit from the hairpin--you could see the bikes coming up to the hairpin and the outfits drifting around the hairpin before drifting into the Elbow.
Worst sight was when I was spectating from the entrance to the hairpin--Fritz Scheidegger had brake problems and didn't slow down or take the hairpin--went straight on, hit the top wall of the hairpin and was thrown high into the air like a rag doll. Terrible loss as he was a really good rider.
Ah well--life goes on!
1 member likes this
#847258 Apr 27th a 06:04 AM
by JER.Hill

If you can machine the crankcase to centralise the alternator/out rigger carrier, then you can also increase the OD to allow you to carry larger engine sprockets. Three counter sunk hole to fit the mounting to the crankcase, then another three holes to lock your out rigger into, this way you can give it clearance for the larger sprocket! To make it one piece there is going to be a lot of swarf, so might be a case of make the crankcase mounting and weld the three leg to carry the out rigger on.

1 member likes this
#848299 May 7th a 03:19 AM
by Mark Parker
Mark Parker
More lift on my 883 made it better, moved the power up. As an 810 it would pull well to 7500 on the data logger about 55hp as 883 those 38mm ports and 44.5mm valves ran out around 6000-6500, and it died, though it had lots better power while it worked 65hp. Offset rocker buttons added about .020 lift. And it was better. And I was able to get 74hp. It pulled to 7,000. But changing the head made 40cfm difference with the port the same size and it's still pulling at near 8,000 and the guy wanted to give it 1000rpm more to see where the graph went over. I wasn't that curious.

It would be interesting to run it again and see what richening it, and better mufflers did, but I don't want to blow it up doing rpm it will never see. A better cam may make it better, if it was easy to swap and cheap.

It's just I measured the std head and extra lift doesn't do much, but different heads can act differently how they respond. And duration makes a difference.

From what I've seen the A65 stock motor isn't restricted by the cam so much as the head. It's not a direct relation ship between cam spec and rpm levels when cylinder head flow is changed appreciably. More air allows higher rpm. If the head is at a good place, then testing cams can show what spec works best.

Why I'm interested in the difference between how the current rig goes with the two different cams. Is one noticeably better? And it's not particularly peak hp but drive.

I'm thinking I should give the Firebird a short dyno and hope the mixture is close and it stays together. It's not like I don't test it on the road but it makes me nervous. Like going home, Deb where's the bike? I need the trailer and degreaser. Should get Ben to take it up.

The head on the 883 didn't make much difference in the mid range, the Firebird feels different from when you take off. And seems to totally transform it in a 650cc kind of way. And it's hard to quantify without a stock one to compare, so I need some sort of test. The SV is out of rego so I cannot do rollons with that which would be easy.
1 member likes this
#848373 May 8th a 01:12 AM
by Mark Parker
Mark Parker
Place in Melbourne done once and no problem. Place in Qld is much cheaper, however it came off twice and the second time destroyed the piston, so cheaper to pay more the first time in Melbourne than twice plus piston.

John Hill in the UK does alloy cyls and Nicasil bores to your piston size. It's more expensive to machine and have bores done here. A JE forged piston can run .002" mine are .0025". I've not tried the 76mm A65-70 pistons EdV does from JE, Just 79.5 and 80mm B44. They work great with the long stroke because the skirts are short. They really need longer rods. I had a taller alloy block cast but never used it.

[Linked Image from]

This is a sketch of the XR750 port. So I'm trying to improve the bottom turn and make everything smooth. And stop break aways and turbulence, the turbulence I think it needs is entering the cylinder and its what it is.

[Linked Image from]
1 member likes this
#850626 Jun 4th a 01:48 AM
by Mark Parker
Mark Parker
So with the 34mm manifold and pwk carb on a big 44.5mm valve head, flow maxes out at 177cfm. This manifold doesn't fit right as the top of it is blocked. It's just a matter of doing a head where it lines up properly and making the port all the correct size and shape. At the moment through that 34mm manifold with radiused entry it's 191.3cfm, a bigger carb will not loose so much but a bigger port loses response.

It looks like making a head with the 44.5mm inlet and 34mm port could be lots of fun, if it can retain the midrange response, and I do not see why not. Low lift flow isn't quite there yet but the seat and port can be better. I need 4 vacs going to test this and higher test pressure. It's just flow calculated from testing a std head. The smaller valves are perfect for stock sized or long stroke motors, but this may be the thing for a big bore 750 race motor when you want strong midrange drive and don't want to exceed 9,000 particularly. It might actually be that carb and port size do not give much more flow than smaller which increases speed and power. I've run my 883 on the dyno once and had a best of 85hp at the wheel and lots of pulls around 83hp but adjusted nothing because the main jets were so lean. So I don't really know what is possible for that big motor, in Vizard's book he talks about getting a motor to finally give 145hp on a dyno and then spending 3hrs fiddling with it to get 170hp. So maybe 95 at the rear wheel is possible with the 883 set up right, if it stayed together and if there was any point.

Problem is I only have a couple of good valves. Which are cut down nitrided Jaguar that I don't seem to be able to get any more. Valve seats need to be central to get these to fit as well, but I think it's worth doing on a 750big bore with lots of compression and a cam. The idea is to make good hp to 7500 and be able to use more at higher rpm if necessary.

Just to add later T/bolts with 40.5mm valves have larger inlet seats so don't need the expense of fitting new seats.

Edit; looking at the seat it's very ordinary but making a better fitting manifold gives a better idea of what is possible. Through the carb at .428" 180.5 .385 178 .350 174 .300 162 if that stays close and is anywhere near accurate, on a finished 34mm port it would be devastating. A 38mm carb and port is only 184 so unless that was increased it's no advantage probably a loss.

[Linked Image from]

The valve is holding the 34mm tube that is squashed oval at the head in place jammed against the cap screws. This head on an RGV needs curved manifolds so Ben is looking for a good Thunderbolt head.

From Vizard's book a std 35.8mm exhaust valve is a close match to a 44.5mm inlet in a 9.5 to 12-1 engine for best power. MAP have 2X B50 44.45mm black diamond swirl valves $40us each.

Do you know what lift @ the valve the SRM cam has Nick?
1 member likes this
#852278 Jun 24th a 01:15 AM
by NickL
Well, ran the old thing up on Sunday with the 650 motor fitted and the head i modified
fitted with the weber. Seems good and sounds lovely, all ready for the 'Big-Chill' meeting
in July.

I've told him to take care of my
1 member likes this
#854053 Jul 18th a 10:48 PM
by NickL
One of the races up at the goat track circuit last week.
1 member likes this
#866836 Dec 20th a 08:35 AM
by NickL
Just a photo showing the simple end feed arrangement i use on a65's.
It maybe helpful if someone is contemplating doing the job.
1 member likes this
#867179 Dec 24th a 11:29 AM
by Twin Pot Phil
Twin Pot Phil
Originally Posted by NickL
Was -1 deg on Sunday morning until about 8am.
After living here for over 20 years i have lost my pommie cold weather hardness.................Nick
Harumph, only 20 years, standards old chap, standards. Don't let the natives drag you down, stiff upper lip now.
(runs and hides in a very dark corner!!!)
1 member likes this
#874569 Mar 15th a 09:40 PM
by Twin Pot Phil
Twin Pot Phil
See Nick, you just had to do some work on the outfit to keep warm!
Don't let minor irritations divert your attention.

Confession, I haven't touched the bikes yet, waaaaayyyy too busy trying to get the resto house (and new large garage) livable, management instructions you understand..........(and the management is an ex-TT and continental circus passenger, so best not argue eh!!!!!)
1 member likes this
#874577 Mar 15th a 11:08 PM
by Ben P
Ben P
We seemed to dodge the rain you got Nick. Still some minor flooding. And I had a week at home last week with covid kids. Progress on my race bike is pretty slow. Waiting for the crankcases to be machined. Im now aiming for 2023 season 🤦🏻‍♂️
1 member likes this
#876241 Mar 31st a 10:50 AM
by NickL
Matt picked the bike up from me last weekend, i had done the brakes
and wiring. The brakes now need bedding in as they are all new, the wiring
was awful, a complete lash up!. I am wondering if the problems we had at
Warwick were due to it. As per normal the race meeting is a week away so no
time for me to set anything up or get it on a dyno etc. They love sailing close
to the wind those guys. I get a bit pi$$ed off though as if it doesn't run right,
it's down to me, i'm supposed to wave a bloody magic wand and sort it. Example
they had a brake 'expert' sort them out last time at huge expense, they were useless.
When i measured the drums, the shoes were nowhere near size etc.
I keep trying to tell them that with these old crates you can't just buy 'go faster' gear
and bolt it on and expect it to work, you have to dig into the reasons etc.
Anyway, i'll stop moaning for the minute, get over this weekend and run it up and see.
I promise you Mark, we will get it on a dyno within the next 6 weeks though even if
i have to do myself.
1 member likes this
#876625 Apr 3rd a 11:16 PM
by NickL
Well, it starts and runs on rollers ok but i wasn't game to ride
it around the streets to test it so we'll have to wait and see.
Looking like a few showers about for next weekend at the track
see how he gets on with the new rear tyre and frame mods.
1 member likes this
#877319 Apr 11th a 05:37 AM
by Mark Parker
Mark Parker
Sorry you are having trouble Nick. What brand chain is it? Old Reynold and Regina seem good. If the sprocket starts hitting the side plates it can break them or force them off. If you look at the old chain see if there are wear marks on the plates.
1 member likes this
#877325 Apr 11th a 06:28 AM
by JER.Hill
Hi Nick

Sorry to hear of the troubles, hope you manage to fix it up.

1 member likes this
#877496 Apr 13th a 12:17 AM
by Tridentman
Hard luck, Nick--but I don't have to tell you--that is racing.
The old saying when I was racing back in UK in the 60s was "If you don't blow the engine every 2 or 3 meetings then you are not trying hard enough!"
1 member likes this
#877501 Apr 13th a 01:58 AM
by koncretekid
I know the feeling. Mine was caused by screws holding the outboard bearing plate behind the clutch backing out and catching the back of the clutch basket. I was at full throttle at Loring AFB, about 125 mph. The broken chain ended up inside the fairing. I was lucky to be able to salvage the broken pieces and get it welded back together again. I added an extra 6 screws to the bearing plate and lock-wired them.

[Linked Image from]

1 member likes this
#877570 Apr 13th a 08:56 PM
by Twin Pot Phil
Twin Pot Phil
Bad luck Nick,
I feel your pain.
My worst mistake (anong many!) was rushing a rebuild to make the next meeting, only for it to go bang again, caused by another problem related to the previous bang that I failed to check thoroughly enough for on re-assembly.

It's a real joy having to custom make go faster parts after the last ones broke!! oh the joy of racing old clunkers!
Mind you it was just the same with the TZ750 - and they were still making those at the time!!!
1 member likes this
#877527 Apr 13th a 11:41 AM
by Mike Baker
Mike Baker
A lot of long nights ahead of you.... Sometimes wonder why we keep putting ourselves through it all. It's a sickness I suppose.

I follow a group on [email protected] Queensland race something or other- They evidently had an event last weekend. I'm guessing that was where this happened?
1 member likes this
#877992 Apr 17th a 11:41 PM
by NickL
Exploded view of A65 primary drive area.
1 member likes this
#878913 Apr 29th a 12:30 AM
by NickL
Good on you Mark, thanks, ill get it sorted.
It's a late 71-72 head so should take the bigger valves.
I actually bought a set of PM ones for it (o'size inlets) and new guides.
This will have ED's JE pistons 80mm. MAP rods etc so your numbers
are a great guide. Crank not finished yet and rods not yet ordered but
it's in hand as they say....... Matt's had a lot of expense over the last few
months so i need to 'go easy' with stuff. He was off work with covid and
the bad weather for quite a while. It's not like you win 'sheep stations'
in this game, trophy's are as good as it gets.
1 member likes this
#879428 May 4th a 03:26 AM
by Mark Parker
Mark Parker
The spline is brilliant. It's a little bit of stuffing around to fit. Gavin would have good posts on it. It looks like jewelry. A gear for every occasion.

All being well we can get a bit more out of the small valves. We'll find out. You are probably right on the money at 12"
1 member likes this
#879921 May 8th a 09:13 AM
by gavin eisler
gavin eisler
Yup, the 5 speed cam plate notches are smaller than the Std 4 speed, ball ended plunger wont fit 5 speed.Enjoy the 5 speed Nick, I had to remove a cuppla thou from the trap door body for clearance, also the lay shaft big gear on the driveside needs some casing clearance, I chewed this out with a dremel, might have been easier to make a dis.c faced with 80 grit
1 member likes this
#881095 May 20th a 04:54 AM
by NickL
The actual main venturis in the DCOE are very smooth and nicely flowed.
The butterfly follows after the main venturi so they are what spoils it, well,
not so's you'd notice anyway. The auxiliary venturis are where the fuel mixture
is dispensed they are before the main vents. These placements are what makes
the carb a large lump but it never stopped them being one of the best carbs made.
1 member likes this
#881166 May 20th a 11:57 PM
by NickL
John, if an idiot like me can get to grips with the webers (well, on a good day anyway)
I'm sure you'll see the see the pro's and con's of them.
I can honestly say that the trouble ive had recently with this bike's carb is the first running
and tuning problem i've ever had with them. AND, that was just my not recognising the
float level problem. Someone with half a brain would have seen it straight away. The first
time he used it it was fine then the next, it was rubbish,,,,,, obvious really that it must have
been something along those lines but it took me way too long to find it. My age is now greater
than my IQ i think............
1 member likes this
#881223 May 21st a 11:15 PM
by NickL
We used to run the old 750 to 8k as a parallel motor years ago.
I spoke to a couple of guys riding them and they said similar so
we'll go with that to start with. Comp ratio will be up at 10.5-1 i
would think, but when we are further forward i'll measure it and
Matt's tried his gopro a couple of times but the stuff out of it
isn't very good.
Sorry about the small dent, it wasn't a little hammer hit i dropped
the head onto the vise while turning it around.
1 member likes this
#881024 May 19th a 11:10 AM
by NickL
LOL, those figures look bloody good, that's a massive increase and
being a small port it should be very good at partial valve lift too.
I used a couple of small pieces of 3mm ally plate in the floor of the
one i did up for Matt's 650 as it had been opened up way too much.
The side wall had broken through on that too so i put a couple of
1mm thick ally pieces in the tunnel stuck with jb weld. That' seems ok
and didn't crack again. Yes, the one you did before is still good, i have
it on the bench at the moment and there are no apparent cracks in that.
Be great if you can get both sides the same as otherwise we will be
limited to oval circuits...............
It seems that the straight tubes are better than angled down as previously
done, i'll have to get the carb end of the manifold modded a little to suit..
Great stuff Mark, much appreciated.

1 member likes this
#881311 May 22nd a 11:23 PM
by Mark Parker
Mark Parker
Allan Price said he used about 11.5-1. The EdV pistons can easy get that in a 744 I think. I bought a burette so I could see precisely and Ben's is just under 11-1 with Omegas. Allan said he used pump fuel, no additives.

On Ben's we have the pistons at deck height and the gasket giving the clearance. Paul's were a bit above it using the nice forged ones. I need to make it around 11-1.

Hacked #2 out this morning pretty quickly. Waiting for JBWeld to set. Not quite the same, but I'll test first. I just want similar flow. When it's almost set it can be pushed into shape. It's sort of good putting enough but not too much and making the shape without heaps to cut. Pushrod tunnel and floor still to be fixed.
1 member likes this
#881530 May 26th a 04:53 AM
by Mark Parker
Mark Parker
Deleted one.

Fitted guides - the left hand exhaust guide hole was tighter using the undersize guide as a guide than the intake hole, if you can follow that. So I put the 2 in the inlet. At 200c and with freezered guides they all tapped in. The other side is the reverse. None just fell in. Now they are cold they all need honing, so even a std valve does not go in. The nitrided ones are fractionally bigger. I got a fancy guide hone a while back because every new guide does this. Crushes in a bit. If you wear them out get them K-lined rather than removing.
1 member likes this
#883116 Jun 16th a 11:03 AM
by NickL
I can scrounge a guide hone as my reamers won't touch that gear.
1 on the inlets and 2 on the exhausts are my fallback numbers when
using PM guides and having done the seats myself, so i'll use that.

1 member likes this
#883181 Jun 17th a 02:05 PM
by Mark Parker
Mark Parker
Ben's 734 is a thing. Adjusted the mixture a bit and a quick spin before dark. Dropped the needles and swapped the bowls for some drilled to supply the power jets? Same 34 carbs from the same place? It's still rich cruising but full noise looks like 12.9 - 1 rather than 14+ but hard to get a look when it's trying to pick the wheel up in second. The power is so strong, and you are just thinking wow.

I ordered a steering damper for it. The engine is right forward but the front gets really light. I don't want it provoking bad behavior. It's more than fast enough for me. I opened it going slow in second, it's just so nice. Wish you could have a go on it Nick. And the cam is std profile. I don't know what it's like above 6,500 - 7,000 but it's pulling very hard into that area.

I'd love to know what hp it's getting. I could fit offset rocker buttons for .410" lift but it would shift power up the rpm a bit. It definitely goes harder than with the 38mm, in midrange and into higher rpm. The thing would have been so fun in the '70s-80s. It has that sharp throttle response.

Nice machining on that bearing plate and support. It makes it harder for cranks to flex I expect. Hope it kicks butt. And all stays together.
1 member likes this
#884171 Jun 29th a 04:19 AM
by NickL
We are all set for the weekend but it looks like it's going to be raining, bugger!

Ran up last Saturday and seems good, no leaks from the welded repairs etc.
Float level seems good and stable and should be ok with the fitted regulator,
although until it's on the track it's hard to say. I've put the jetting back to a
sensible set up ready to test in practise. Don't think there will be many there
so it'll be a good setting up scene for the Qld titles at Morgan Park. Some more
mods to the frame have been done but we know there are one or two things
that will need adjustment, toe-in etc. I also put new rings in as the bores needed
a fair amount of honing so they'll need bedding in, hopefully the filters he's fitted
will stop the crap getting in.
Hoping for the best, and wishing for a dry weekend............,.lol.

1 member likes this
#884731 Jul 5th a 03:06 AM
by Mark Parker
Mark Parker
It's a real credit to you guys to get it to do what it does. Not blowing stuff up is definitely the trick. I have an old rusted A10 crank on .040" under and rusted I don't think it's good for anything. Not when Chris can get a std one welded to 84mm stroke. My friend did that in Melbourne as well but a bit longer stroke.

With a base gasket you have to adjust tappets, same with not venting into the primary, you have to check it has oil sometimes. It's bad enough they wear tyres out for me.
1 member likes this
#887596 Aug 6th a 04:02 AM
by NickL
Well, after a little deliberation i ordered a 20 thou head gasket from Lani at Copper
Gaskets Unlimited. It arrived the other day (took less than 2 weeks) and is a lovely job.
The fit around the studs is really good and general quality is excellent. It was only a few
dollars more than a standard one (plus post of course) but what a difference in quality!
Thanks to Trevor (WM20) for the recommendation, will definitely use them again.
Managed to find a set of 3 piece oil rings from an early 750 trumpet (75mm) so will fit
those as well. The Venolia forged pistons need 3 piece oil rings really as they use 8 thou
clearance, Standard one piece ones tend to make it smoke a little.
So after cutting a little more from the piston inlet pockets we should have around 11-1 now.
Not measured yet but it's one on the 'to-do' list.
5 speed box is in and 8 plate 3 spring clutch with my old srm pressure plate and some decent
springs. All seems good, we will see..........................
1 member likes this
#887654 Aug 7th a 01:11 AM
by NickL
Yes it's one i bought from Gary at SRM about 30 years ago.
I also bought a few spare bits and pieces for those pressure
plates at swap meetings over the years so i have a few of
the radial bearings and end stubbs/pushers.
I tried a set of my old 'Gorilla springs' in the clutch but it was
bloody heavy so i just put some t120 springs in. It runs very
close to the cover with the extra plates so the springs have
to be almost flush, With a set of my old ones in there you
almost need two hands to operate it lol. I had a special/funny
clutch lever/cable arrangement on my old crate and even then
after using it for a while i could strangle crocs with my left hand.
1 member likes this
#890826 Sep 15th a 11:33 PM
by Mark Parker
Mark Parker
Thanks John.

So here is a great photo of the protagonists.

[Linked Image from]

Chasing the big Norton with the 650.

[Linked Image from]

[Linked Image from]
1 member likes this
British Cycle SupplyMorries PlaceKlempf British PartsBSA Unit SinglesPodtronicVintage MagazineBritBike SponsorBritish Tools & FastenersBritBike Sponsor

© 1996-2022
Powered by UBB.threads™ PHP Forum Software 7.7.5