Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Nourish A65 Motor

Hi everyone,
I have just bought a 1969 A65 bottom half. It has an SRM end feed conversion, running into a 90 Deg. NRE crank. Yesterday, I phoned Mr Nourish and he told me from the number stamped, that it was balanced to Carillo rods. It still has them. They are 6" and the crank throw is 90mm. I also have a standard top end ready to use from another motor. My question is Do I have to use a custom cylinder/piston/head arrangment? Can I use a standard A50/A50 top end and see what it feels like? Anybody done this? Needless to say, i have split the cases, and upon inspection, all seems in very fine fettle and ready to use.

Kind Regards and a VERY Happy New Year to all!!

Make sure that you have a camshaft that matches the new timing of the crank. The cam timing of one side will have to shifted to the 90d. A65 pistons will collide with the edges of the A50 combustion chamber. Either the pistons or the head needs to be modified for clearance.

If mine, I would use a standard A65 head & work out any problems with the 90d setup first, like how to fire the cylinders at the correct time. Cheers, Don.

Sorry I forgot to mention, it was put together by SRM using a special 90 Deg. cam which is also included. I also have a Lucas Rita ignition supplied by them for it. It was originally done in 1998.

Kind Regards and a VERY Happy New Year to all!

Congratulations on your purchase.

Mark Parker will certainly know which pistons you will need, can't imagine him not joining this conversation as soon as he spots it. Not sure how early he hits the computer on New Years Day though. I think it's just after 5:00am where he is.

Another person who would know would be Ed at...
E&V Engineering

They're a sponsor here and word has it that the pistons they supply are absolutely deluxe.

Hi.
In my a65 bore & stroke 77 x 85 (Nourish crank) I use modified Triumph T140 pistons (the valve pockets needs grinding because of different angles). A65 pistons cannot be used. Std a65 cylinders can be bored out to 77mm without any risk. I used std cylinders 77mm for a couple of years before buying alu.cylinders with nicasil (also 77mm) from Rainer Traupel in Germany.
If you can find T140 high comp.pistons there will be more material to deal with.I found TRW h.comp.pistons on e-bay.
The a65 cyl.head will not need any modifying.

Regards

Nice, any pictures? If you intend to use stock pistons then the barrel has to be taller for the longer stroke. I do not know off hand if the wrist (gudgeon) pin can be moved high enough in a special piston to keep the stock barrel. Taller cylinder also requires longer pushrods. You still need to clay the pistons and check for valve interference in any case.

Here's the picture that was on ebay. The GC serial number puts it off the line in June, 1969.

Ed V has forged A70 pistons that would be ideal, A70s have 85mm stroke and a higher pin height in the piston to suit. His pistons and ring packs are very good, I use his B44 pistons in a big bore cyl. If they are a little more expensive than cast, its because they are better quality and worth it, actually you probably wouldn't find A70 cast pistons anyway. T140 pistons are OK but the valve cut outs are for a Triumph and need re-doing, so its probably cheaper getting the A70.
The crank is ballanced to the rods, but did he say anything about piston weight? Close probably would be OK so long as they were the same, it would just vary the factor a little.
Anyway looks like you got some good bits, hope you keep us updated on the build and how it goes.

My only experience is with my A50 Cyclone motor. I'm really not bothered about cubes, as long as it's "Sweet". With this in mind, I would like to be able to construct another A50; but, being a realist, acknowledge that this probably isn't going to run at all well, probably not possible at all. So, I think I'm looking at a big bore kit, though SRM closed until the 3.1.12, can't talk to them yet.

This was the idea of posting, just to gather some options. I'm grateful for the info so far, and yes, the photo previously posted is of my motor. BTW, not pictured are the clutches, gears and other sprockets included. The idea of a 90 deg. engine is the primary motivation for this project, not a hot rod/street racer/thing.

I'm now off to bolt the cases back together and fit oil pump, gears, timing cover etc. I've taken the advice of a local 72 yr old "Legend" round here, and I shall not worry about balance 'till it's running. "See if you like it" -Sounds good to me. First though, is the small problem of finding a top end solution. Thanks again.

A VERY Happy New Year to all!

I don't think SRM are doing long stroke B/bore kits, these have the taller block, their 750kits for std 74mm stroke motors uses a B44 based piston with similar pin height to an A70-T140 and their block is shorter to suit. A70 pistons in a std 650 cyl with A65 head will give you 750cc and plenty of performance. And is probably a not too expensive option.
I wouldn't put an A50 top end on it, even if you did you would need special pistons, plus that cam is probably 'race' orientated and better in a bigger motor.
750cc would be a good size.
I'd recommend fitting 520Xring chain and sprockets while you're at it, and tall gearing.

A note about gearing, with a 90deg 750 B/bore std stroke, my brother runs 20-40 final gearing. He uses a different back wheel. If you are stuck with a BSA wheel and 47T sprocket go as big as you can on the front, I think there is a 22t in the photo, because the 90deg will pull better. This is the sort of sound you can expect:
http://www.youtube.com/watch?v=vBtY6y8rXls&feature=related

That sounds good Mark but I always felt that this clip was awesome.
http://www.youtube.com/watch?v=oBD2...wUtLg-Y8dA&index=15&feature=plcp
Amazing. Doesn't sound much like my A65!

Got home from work today and phoned SRM, spoke to Gary. Yes they dont have the larger kits at the mo, only the shorter length barrel kits. It looks as though I have a hot cam as well, so will be looking to change that to a spitfire profile. I need a barrels good enough for a 90mm stroke crank. I may have bitten off more than I can chew, yet I feel compelled to finish it. Dave Newman can reprofile the cam in the UK, so I will start there.

Kind Regards

Thanks Alan for taking the time to photograph the heads. At the moment, I'm not looking for another head just yet, as I want to explore the Barrel/Piston choices I have. I am lucky in that I have some very capable machinsts willing to help me out. Also, one of them is a sprint bike builder. Nothing scares him! The aluminium/nikasil option seems the way to go, so I will phone Rainer Traupel when possible.

Inlets I use are 44.5mm, exhausts are 39mm (cut down Jaguar, the exhaust valve head was also reduced in diameter) this is an old head, welded for more comp with T140 pistons, it was around 11-1, and a bit hard to start, a better ported open chambered head with the same valve sizes and less compression gave better power in midrange and top end.

This head had 36mm carbs, 38s worked plainly better. We have run a 90deg 650 with these valve sizes and 38mm flatslide carbs, I think it was similar to a std 650 down low but after 5,000 hit a fierce power band like a two stroke. This shows the ports, I now 'D' the port by filling the floor a bit which brings power in earlier without loosing anything later.

So is the crank 90mm stroke Gavin? I use 89mm with rods a little longer than Commando rods but shorter than 6" It takes a bit to squeeze everything in. You will probably need to open the crank case mouth a bit for an alloy block.

Hi Mark,
In answer to your question, the crank has 90MM stamped on it, but when I spoke to Mr Nourish, he said 84, but I think he was referring to the A10 dimensions? (He was trying to do some mental arithmetic out loud).On measuring the difference between BDC AND TDC, it's between 85-90. With steel rules, I'll measure across the crankcase mouth, to get an accurate figure. Spoke to Mr Traupel today, and he says he can make barrels according to my requirements. When we speak again in a week, I'll have the correct figure. Meantime, I think I'll get some A70 pistons from E&V.

Kind Regards

Hi Everyone,

Just an update. I now have a Devimead big bore head for it, c/o a Britbike member here, arrived in a timely fashion thankyou. Also on their way is a pair of E&V pistons, a sponsor here, and last but not least, I've got some aluminium/nicasil lined barrels on the way from Germany, c/o recommendations from members posts here. It makes sense really to have the aluminium barrels, as the heat from modern soup/"Fuel" makes our old motors suffer in their standard form one way or another.

Gavin, do you have specs on the 90deg cam? If I were you I'd use it as is and see how it went, big motors can tolerate bigger cams, it may run very sweet with it. Hope your bike has good brakes.

Brakes? Standard 1965 Single sided 8" front, standard 7" single sided rear on 42T Sprocket, QD hub. I'm more worried about the QD hub to be honest. The torque generated might destroy it.

Very interesting project you've got on the go there Gavin.

Bore to stroke ratio will be about the same as an A10, so it should be very sweet to ride once she's all sorted.

Yes John it is, that's what keeps me keen to see the results. 5MM or so over BSA Block height, means longer pushrods. My sprintbike builder friend makes his own pushrods. Using VW items, which are "Exceedingly" long, they are "Cut'n'shut" to provide the required length.

Kind Regards

Ok, run into a bit of a problem. I've collected the pistons from the Parcelforce depot today, and lovely as they are, they won't fit without some headscratching. These things are sent to try us! Of course the gudgeon pin dia. is. 750", but my conrod small end bush will only accept a .688" The conrods are Carillo forged steel, and I don't think I can just ream ream them out, as I don't think there's enough meat left. Can anyone suggest an engineering solution please?
Kind Regards

Gavin

Looks like the rods were probably made for Norton Commando pistons, according to Carillo page 40.

Perhaps there would be a machine shop solution by modifying/bushing a set of Norton wrist/gudgeon pins.

Ok, I have a C25 piston, and it seems that this is a perfect fit onto the rod.

Any progress Gavin?

Gavin,

In your shoes, I would grind about 0.100" off the length of the wrist pins (or use the shorter C15/B25 wrist pins) and make a stepped bushing to go over the ends of the wrist pin that is a tight fit. on both the wrist pin and in the piston.

I'll see if I can knock out a drawing later if that doesn't make sense.

I just saw the note about your worries concerning rear hub strength. I say this with a grain of salt and hope I'm not cursing myself but, I have been running the QD hub on my LSR raceer for 5 years and that hub is hangin in there ok. We are putting over 100 hp to the ground so your set up should be ok. Cheers, PRT

Similar to the cups on a u-joint, except no rollers, just a tight friction fit.
The walls are going to be pretty thin though, about .030" unless the diameter of the pin is reduced.

Another option would be to get a new set of rods made up to the proper specs. Selling the Carillo's should recoup a good portion of the cost.

What sort of ignition system are you going to run on the 90 degree set up ?

So I'm guessing the rods have a bushed L/end, what is the o.d. of the bush? If removing the bush makes it close to BSA pin size maybe the rods could be machined exact and you could get pins with DLC and run with no bush. Other than that custom pistons with Norton size pins, an advantage of this is you could specify less dome, when the swept volume gets bigger and the chamber volume above the piston stays the same, comp ratio goes up, if that dome in with a 84mm-85mm stroke gives 10.5 - 1 a 90mm stroke will give more, you can run them lower in the block for less comp but if I was getting them made custom I'd reduce the dome. Either way emailing Ed V I think would be a good idea. I wonder if that means the big ends are Norton size, if it does its a good thing to have the extra dia and strength in the crank.

Thanks for the input on this from forum members. Update: I have bought some new SRM Plasma hardened valves, and they are being fitted at the machine shop, the inlets being their 43.5mm Dia. I have removed the rods, Thanks for the reassurance PRT, I was thinking of sidecar requirements. I'm glad I've got the E&V pistons, not least because of the quality of the rings. Correctly measured, the rods are in fact 6" long. Can't accurately measure the little end 'till I push the bush out. In answer to bon, I spoke to http://www.electrexworld.co.uk and http://www.kirbyrowbotham.com, who said they could supply a kit much like the usual Boyer type for £225. This would fire like a Ducati and fit in the points housing of a BSA. Now the rods are off, it would be interesting to see what you mean Alex, by a stepped bushing. Can't do anything 'till Monday, so I'm open to all suggestions.

Kind Regards

The outside dia. of the small end bushing is probably ca. 20mm. To ream that ouy to 21 - 22mm would not weaken the conrod too much and then make a bush of chrome moly steel with inside dia.19mm (std a65). I have sucessfully made such thin wall steel bushings for the worn out small end on several Honda twins (Black bombers) which have the gudgeon pin running directely in their c.moly conrods.

Regards

Gavin, with ignition it's preferable with the odd angles to fire the plugs individually. Pazon are working on an 'Altair ign' for singles, that only fire the plug when needed, with no idle spark, when they get the kits done I'm hoping to get two and use a modified ign plate to fire both individually. I'm using a Honda VT250 ign at the moment that is individual but it has excessive adv, the long stroke motor seems best with around 28deg only. So to get that its a bit retarded down low with an advance that doesn't even start till 2,000RPM.

Well I have been busy recently. Have just got back from Coltec Racing, in Hollesley, Suffolk. They are what's left of Holbay racing, anyone remember them? Richard, said he could make a new bush that would work ok with the Carrillos and E&V pistons, so I am very relieved to hear that. I also took the crank, and upon inspection, it needs a regrind and a good clean as it's had a hard time from the po. The only people he knows of able to do the job are in Coventry and I shall drive it there, unless anyone knows different. He has a production quality grinder, but it's out of commision at the mo. An ordinary grinder "Won't do", as they are only good enough for regrinds and not suitable for a crank like mine. His words, not mine. Now off to see how the head's getting on. Ttfn.

Hello Gavin

What bore did u choose for the nicasil, alu sylinder ? How much longer than stock is the cylinder from Traupel ?

im assembling a A65 engine now.
I use big bore cylinder in cast iron from SRM that is 8mm shorter than stock A65 cylinder. It forced me to make very very short conrods on 157 mm. I have a Norton 89 mm stroke crank, Ed V 80mm pistons. From Bsa B44. I'm worried about the flexing of the crank and the short conrods. My crank is stock 360 degrees. I Consider the alu cylinder to, but as I understood from Traupel, the limit of bore is 77mm

Andreas

Hi Oleandreas, I have only spoken to H. Traupel twice, but I've now agreed with him to make a set with 77mm bore. This will fit my +.080 A70 pistons from E&V. Stroke is 90mm, with standard length rods. The overall height of the standard motor from the cankpin to the piston crown base is 37+152+30, mine is 45+152+30. given the first figure is half the stroke, the other two constant, as the rod length and pin centre to crown base. Therefore, 8mm over standard height barells. The exhaust was a standard size. The head's not ready yet.



Kind Regards

Just some more information, for a more straightforward job, you can use a Norton crank, (89mm stroke), Triumph rods, and T140 pistons, then remove 1mm from standard height barells. This makes a revvier motor I guess.

Kind Regards

Hi Gavin,

Your numbers seem slightly off.

According to Ed V, "The standard A65 compression hgt is 1.415" at least on our pistons". 1.415" = 35.941mm.

For a standard A65...
Stroke = 74mm
Rod Length = 6" = 152.4mm
Compression Height = 35.941mm
This suggests that block height is 225.341mm as that is where the piston deck will be at TDC.

Again, according to Ed V, "A70 compression hgt is 1.218"...", in reference to the same pistons you have.
1.218" = 30.9372mm.

For your A65 motor...
Stroke = 90mm
Rod Length = 6" = 152.4mm
Compression Height = 30.9372mm
This suggests that your piston deck will be 228.3372mm from the center of the crank at TDC.

That works out to 2.9962mm more than standard, call it 3mm. Your custom cylinders should probably be 3mm taller than a standard set of A65 cylinders.

If I'm off base here, please show me where so that I can correct this chart.

Given a 3mm taller than standard cylinder, it looks to me that your compression ratio will work out close to 10.3:1 with a 1.5mm head gasket.

Hi, from what you have written, TA, one would assume that I have incorrectly measured standard piston compression height. However, I can assure you that I measured genuine BSA A50 pistons from the pin dia. to the crown base/deck and they are 30mm give or take a decimal. Yes, E&V pistons are 30mm also. Therefore the only difference in the "Crank to crown" height comes from the different stroke, i.e. 90mm instead of 74mm. This means 45 instead of 37 in terms of the throw, yes? A difference of 8mm... As I understand, A50 AND A65 barells, although recognisable by the different amount of fins, are in fact the same height. This is how I have done my calculations. I am ok to take a hit on this if anyone knows different, measure a genuine BSA piston for yourself...

There's the issue right there, A50 and A65 cylinders are not the same height, nor are their pushrods the same length either.
The fact that the A50 pistons you are measuring have a compression height of approx. 30mm shouldn't really have any bearing on the cylinders you are having made, I would be very surprised if Rainer's cylinders weren't based on A65 height rather than A50.

Ed V was very specific in his response to my questions regarding compression heights of the pistons he sells, you should certainly be able to trust his figures.
Scepticism of my calculations probably isn't really a bad thing though!

Ok, as I said in my previous post, my only experience is with my A50. I do know however that pushrod lengths are different for A50 and A65. I too have spoken to Gary at SRM, and he said cylinder heights are the same; or is something lost in translation? Do you have a set of both please to compare?

No easy access to the pistons at present.

The cylinders though measure approx. 5mm difference in height with the A50 shorter than the A65. 3.7" and 3.9" approx.

1969 Royal Star and 1967 Lightning, in my workshop, five minutes ago.

Perhaps Gary meant that the height of the SRM Big Bore barrels is about the same as the A50. A65 cylinder height is the same as A70 cylinder height.

You are comparing an A50 piston with a 74mm stroke to an A70 piston with 85mm stroke. You used a 74mm stroke for the A70 which is also throwing your calculation off by 5.5mm.

According to Ed V, the compression height of the A65 pistons he sells is 0.197" more than the A70 pistons he sells. This works out to 5.0038mm.
It all points to the A50 cylinder being approx. 5mm shorter than the A65/A70 cylinder.

No it's 4speed with an extra cog sitting on the shaft, I was watching as well and asked.
I have read of people using A70 pistons in a short block to pass it off as a 500.

Ok, its not nice having your parade rained on, but thanks to forum members, I'm going to have to phone Rainer again and ask him nicely, as I've already stumped up 600Euros deposit, if he wouldn't mind making them 3mm taller than standard, yes?

3mm should be good, based on the info you've provided.

One thing still concerns me though. Your con rods, make absolutely sure that they really are 6". The Norton size little end makes me wonder if the rods themselves aren't Norton length as well. If they are, they are 3.175mm (1/8th") short of 6" and the barrel you are having made would need to be the same height as a stock A65 barrel!

No rain, just sunshine!

Hi Two Alpha, Yes they really are 6" measured with my steel rule. It's comforting to know that others reading this thread are learning something as well, maybe. (Or maybe not). I don't mind admitting when I've got something wrong, and clearly I did in this case. I'm grateful as I said to Forum members, for giving me advice. After all, that's what a forum is for, n'est pas? Rainers ok about the height issue, BTW, the casting is big enough to accomodate the tall height anyway, only when the machining takes place, does he need to know exactly.

BTW, try finding anybody who can do this for you in the UK, as professionally as Rainer. I doubt you can, but then again, that's what makes Britain "Great", isn't it? I'm not such a tenderfoot as to realise the economics of it all either. I can't bring myself to use a silly icon, so I won't then.

Kind Regards

I'm a European, believe me. I'm too old for all this anti "We will be putting our country's interests first" mularkey. A century of war has brought us back to the caveman mentality. I believe we should look to the future as part of the European project. Union is strength, we couldn't punch our way out of a paper bag on our own. No more politics please, this is my thread. (Or I won't play anymore)

Kind Regards

Been a while since my last update, and I need some advice please. Ok, so the A70 pistons now fit the rods after some reaming and scraping of the small end bushes, and I have got the cylinder head back fitted with new big valves. I should pick the 90 Deg. crank up today after a - .010 big end grind. I've also had a nickel weld repair on the pinion keyway, and of course the compulsory oilway clean.

My next issue is with ignition. The motor came with a Lucas Rita box and a special reluctor made for SRM by Mistral Engineering back in '98. Mistral tell me it would have about 34 deg advance, and I'm OK to try to set this up, but having spoken to SRM about it, am told the max advance I need is 28 - 30 Deg. because of the long stroke. I am concerned then, that it would be difficult to start, because of a retarded state at cranking speed. Do I need a different box? Is there an alternative method? Can I run lights or do I have to settle for daytime running only?

I'd be setting it about 28deg total, I'm sure the Rita will work fine. I have used one. I'd guess you would still have 5deg advance when kicking. I'm using a Honda VTR250 ign at the moment and it's less suitable, probably idling at 0degs or even after TDC, and it doesn't advance at all till 2,000RPM, but it's fine when running and will idle ok, but is a bit hard to kick start, though bump starting is instant, this may be due to something other than ign timing though. At least when I use the kicker its less prone to try taking my leg off. I don't think more than about 5deg advance would be very wise when kicking these long stroke motors.
Andy at Pazon said they are in the process of doing some altair ignitions for singles, I'd like to run a pair when he gets them done, with idle stabalization as well as one spark only when needed, no idle sparks.
If you look in this link under 'features' it shows the altair ign curves for twins.
http://www.Pazon.com/ignition-system/altair-twin

I can't see any reason why you'd need less than 15 degrees advance at idle,with no further advance until about 1500 rpm.Real men can start real bikes locked on 35 degrees full advance (without breaking a leg),and they start OK and idle well;but you can't lug the engine below about 3500 rpm.Also,if you open the throttle too much when starting,you can break a leg or an ankle.
If there is no further advance between cranking speed and just above idle speed,you get a stable idle.

Maybe the long stroke requires less advance because you don't need such a high piston dome for a given compression ratio.5 degrees retarded is a lot for just having less piston dome for the flame to travel around.The flame must also travel further now,to get across the bigger cylinder bore.
31 or 32 degrees full advance could be about right.If you have say 12 degrees at idle and 32 degrees full advance,that means 20 degrees advance built into the ignition system (not 34 degrees).

If you need to turn it back to 28 degrees full advance,you'd still have 8 degrees at idle.
8 degrees at idle is less than ideal,and the engine will run hotter when you're idling in traffic,as compared to 12 or even 20 degrees.

Just my thoughts.Most electronic ignition advance curves are not quite ideal.

Thanks Pete for your observations. Youve hit the nail square on it's head mate.
"If you need to turn it back to 28 degrees full advance,you'd still have 8 degrees at idle.
8 degrees at idle is less than ideal,and the engine will run hotter when you're idling in traffic,as compared to 12 or even 20 degrees."

This is the other side of the coin, and I have experience with this, just retarding a standard A65 unit isn't going to give bottom and top end satisfaction. Perhaps a Norton unit then? All contributions gratefully received..

I ran my A65 big bore for years on a no advance mechanism. special oldham drive with outrigger bearing, it ran and started very well. Your project is fascinating, are you going for a clutch outrigger bearing like Mark Parker's?

I think it needs to be realized even though we are talking about timing in degrees the long stroke and different rod ratio effect where the piston is at in the bore. So I think comparing timing degrees to a 74mm stroke motor is not particularly relevant. Doing a heap of dyno runs showed where the timing was most effective with an 89mm stroke and around 10-1 compression with my motor. It doesn't seem to generate an unusual amount of heat idling. I'd be happier with 5 to 7deg adv at idle, because it may start better, but more than that with my old carbs it may be difficult to keep the idle speed down.
The Pazon altair advance curves for twins all seem the same, just set different. Gavin I'd try the ign you have, at least to begin with.
I'm sure you are going to have a lot of fun when you get the thing going.

It's that Nourish thread again! I have some updates to share: Firstly, the hot cam that came with the motor has been sold and I have purchased a spitfire profile 90 deg. job from SRM. The cylinders have come from Germany and I have left the complete engine at Coltec in Hollesley Suffolk, for compression ratio calculations. From the beginning, it was obvious that if a radical ratio was to be avoided, considerable amounts of material would have to be removed from the pistons. This is being done to hopefully result in a 9:1 / 9 1/2:1 ratio. After that, it's all ready to be assembled, with the crank, rods, head, cases, cylinders all ready. Should be 1-2 weeks now.

Good show Gavin!

Why are you aiming for such low cr ? My A10 is quite happy with the 10.5:1 cr. I wouldn`t be afraid of running high cr.
Espeially with that spitfire cam which isn`t exactly small iirc.

Back again folks. Assembled motor is in the bike. All ready to go now, it's just awaiting the ignition. After much debate with "Knowledgeable types", and furrowed brow stroking; I have acted on a C5 kit from Wisconsin. I have fitted a Thunderbolt head with at the mo, a 28mm MK1 Concentric. In part, because it will be easier for me with limited means/time to set up the fuelling. Just to recap, it is a 90mm stroke, 77mm bore 838 motor. The kit has been posted/ will come with four pre programmed "Curves", 30, 32, 34 and 38 full advance figures. What do the panel suggest I start with?

Regards

28deg max is what I'd set it to.

Hi Mark

Thanks. It's what I thought too, but C5 thought it too low . I didn't buy the optional plug in $70 tuning thingy, perhaps later. I'm going to start with 30. Better advanced than retarded as they say.

Exhaust system is interesting. I won an auction for a pair of used Unity TT pipes, which I may fit, or a kind soul has offered a pair of A10 Spitfire high level pipes. Don't think It'll go well with the rearsets I prefer. Just get it running is my priority, so any combination might be fitted later, including my standard siamese or 2 into 2, but without rearsets. Spoilt for choice. I dialled in the cam with a three keyway wheel, and the original timing marks were irrelevant. The kit looks great, just pinpoint exact TDC, and you pick your curve. Getting close now.

When we talk about timing using the C5 ignition (PowerArc based technology) there are two aspects. First is what advance is used at zero rpm and the second is timing at idle.
We usually set timing in the 10-12 degree area at zero rpm with an idle set around 20-22 degrees.

I recently played with my Ural and increased start timing from 10 to 18 in small increments. The engine did NOT start better with more advance but did have a greater tendency to spit back. I went back to 10 degrees.

Timing at higher rpm is set on most engines to 36-39 total advance for street ridden vehicles using readily available pump gas (petrol). This ignition multiple sparks at all rpm and engines respond well to the timing we've set. The system is rpm based and can be adjusted while riding.

NickL I think you may be right about using a single carb. If one piston is halfway down its induction stroke, is the other piston beginning its induction too? Or is the second piston beginning its exhaust? I'm back from a good 80 mile high speed run, and one cylinder is noticably richer than the other.
I am thinking that the first piston's mixture is compromised by the other as it now has to share the fuel halfway down its stroke.

Me thinks the carb is too small for that big a motor. I would aim for a 30 or a 32 mm Concentric on a single carb head.

Are you sure you are not burning a bit of oil on one side?

I'm with Nickl on this one. Go with the twin carb head and get rid of the balance tube (?) Once you get it running right then try the balance tube. Baby steps.

Hey Nick, do you think a balance tube messes up the carburation on a 90deg? I have a balance tube on mine? And it seems ok. I'd probably have to adjust the carbs if I blocked it off, but it might be interesting to see.

I use the balance tube on my 76% also. Dick

Thanks for the replies everyone. What I have is a 30mm Mikuni set up for a 650 BSA, but with the clip at the bottom and a 280 Main, seems to be ok.
With regard to the cam, as its such a torquey motor, I cant see my personal need for hot cam for my riding style, so a Spit profile will do for me.
I do have a twin carb big valve head I bought from a visitor here, but although I prepped it for use, it has had a hard life, and some gorilla has drilled at an angle through one of the studholes, maybe done at the factory: I dont know. This will need further investigation I think as to suitability. It has also been planed to death, and I dont think the carbs would have anything to mate with on the inlets! Its not a big job for me personally to swap heads, and I have another matching Mik, so I think the best bet is buy an un messsed with TC Head.
I am very pleased with the C5 Optical ignition system, it starts 1st or 2nd kick everytime.

Back here to post updates. It now has a T/C head on it and 2 30mm Miks, balanced to perfection. No balance tube, 240 mains, running at 30 Deg full advance. I think I will order the programming kit from C5, just to see what can be achieved with different dialled in curves. Its proving difficult to find time to ride and test it. Really quick compared to anything stock, its more like a Guzzi, but still retains its BSAness when bimbling through towns here. First off, I'm going to 220 mains, as I nearly emptied a tank yesterday, and I only did 70 miles, WTF? I'm getting different signals regarding timing. With the optical kit, (And three sparks per cycle) higher full advance is claimed by the makers, and I can easily switch from 30 to 32, 34 and 38 without buying the programming kit. Visitors here suggest 28, which is not the be-all-and-end-all, but more importantly, its the way it gets there. Any advice greatly appreciated

Programmable ignitions IMHO are the best dollar per dollar mod you can run. They take up the slack of all the other systems combined. Especially if you can set specific timings to specific rpm-s.
I found for me, the best use is in starting rpm on kick only bikes. Set an initial timing of 5-10* BTDC below 300-400 rpm, and the bike kicks like butter. As soon as the rpm hits 400ish advance it to whatever timing it likes 28*-30* whatever.
Same goes for those "hot spots" where the bike tends to detonate. Just roll off the advance thru that range, and re apply it after.
If you like HI rpm, dial the timing into a straight line down toward 0 advance from say 7k to 10k. It will allow the engine to over-rev without grenade-ing. This helps if you break a chain, miss a gear, blow a clutch, climb a mountain, ect.

Fuel mileage is a whole nuther story. Power, and rpm improvements always equal increased fuel consumption. I've taken 60MPg bikes down to 20MPG, and 100MPg two strokes down to 15MPg. It's just the nature of the beast. I would be careful compensating with jetting to increase mileage. Without an O2 sensor installed or an Exhaust gas Temp. gauge you could lead into trouble.
I'm sure you're on to this...

On the other side of the coin, if you ride like an old lady... you might keep some of those miles in the tank. Maybe...

The fuel consumption issue, I have traced to a leak in the fuel tank, (Its 50 yrs old you know), what a bugger, so Ill be replacing that I think with an Indian made one. I hear they are ok. Nah, I've taken it to Sheldrake and Wells, in Ipswich, about 2 miles down the road from my place for repair.

LOL... Where I live, 2 miles gets you to a phone where you can start calling to find a shop.

One issue down... ???to go?

C5 tell me they are waiting for another batch of programming kits, and I am to reserve a place in the queue for a unit $75, plus duty no doubt. Tank should be back tomorrow, so it's off to Cawston, (A 50 mile trip) [Wow}, to have it professionally lined. I have a good painter contact, and the paint code I use is,{For anyone interested} Renault (B12) No 1 Beige Metallic, K1 Aquabase) This will mean more to a paint man I'm sure. Suffice to say, that it is a wonderful old gold, good enough for my UK&General Export 1965 requirement. He did my sidepanels already, and they are exquisite.

Having a blast programming the C5 kit, got a Guzzi curve emailed from Wisconsin, but I will try my own 29 deg. one first.

Here is a Guzzi curve for reference:-