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Ok, as some of you may know, I've been running Mikuni VM32s on one and then another of my A65's since 1984. But now I'm thinking about converting back to AMAL Concentrics. I have a pair of 930's that I had rebuilt at Lund's with sleeved slides. The Concentrics came off a 1976 Triumph T140. I'm pretty sure the carbs were original equipment on that bike, and it ran well with that jetting, which is as follows:
- Main jet: 180
- Slide: 3.0
- Needle jet:.106
- The needles have no markings on them.

A while ago someone posted a link to a listing of factory jetting for various years and models of BSAs. Does anyone know where to find that document? My '66 and '67 Spares manuals only have jetting specs for Monoblocs.

I'm stuck with these slides, so I'm hoping 3.0 is appropriate.


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Ok, I found a 1968 Spares manual online. Unfortunately, the Lightning calls for 2.5 slides! Is this a show-stopper?


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All the later 69 -71 A65L s used no. 3 slides, 68 was the first year of the conc, later settings are probably better?


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Hi Mark,

I have had pair of Lund-sleeved Concentrics in the past. Great work as far as I can tell The bike they are on runs nicely.
3.0 slides are IME fine on any Lightning, as also stated by Gavin.
The standard main jet for the 69 Lightning is #190, needle jet .106" is fine. My own bike runs fine with that jetting with Pancake filters mesh-type, no paper.

So from my perspective you are good to go.

I'd recommend to install new needle jets and needles anyhow, as they do see significant wear and tear due to the vibration.
The correct needle is the standard-4 stroke needle with two rings above the needle clip grooves.

Good luck!

Cheers!

Phil


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Originally Posted by Mark Z
Ok, as some of you may know, I've been running Mikuni VM32s on one and then another of my A65's since 1984.

these were lightnings? ive never managed to fit a Mikuni in between the head and the frame on a thunderbolt.


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Originally Posted by kevin
Originally Posted by Mark Z
Ok, as some of you may know, I've been running Mikuni VM32s on one and then another of my A65's since 1984.

these were lightnings? ive never managed to fit a mikuni in between the head and the frame on a thunderbolt.

Dual carbs, yes. Require use of homemade air cleaners (oiled UNI foam over wire mesh) in order to fit between head and frame. This is one of the reasons I want to convert back to Amals.


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this is an option i hsve been considering for BSAs. it would require some thought on filters but lots are available

[Linked Image from i.imgur.com]


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it is possible to resize the cut away ( but you can only make it bigger) by careful filing ...

grab slide in a vice at 45 degrees so cut away is horizontal and take FLAT cuts with a file ... put something flat across the non cut away part and measure the height of the cut away ,,,, use a known 3 for the gap ...it works ,,, hope this makes sense


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Mark Z Offline OP
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Originally Posted by kevin
this is an option i hsve been considering for BSAs. it would require some thought on filters but lots are available.

I tried something like that once, but it put the air cleaners right into my thighs when I put my feet down, and it looked like hell. Also, you need something very rigid for the coupler, or it will "breathe".

There's another approach to this, one which I don't have the inclination to try, and that's welding a flange onto the carb so it can be bolted directly to the head.

Another reason I want to convert is that the bike had more low-end grunt and a crisper idle with the Amals. The Mikunis are stronger and faster "at speed", but they're soft right off idle, presumably because they're 32mm. (Maybe that's why my clutch has lasted so long!)


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i run 34mm VMs on my 1972 T120, but its got a morgo on it and has some mild head work.

bottom end has a bit too little vacuum, but im running 8 degrees retarded too


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Originally Posted by Mark Z
Ok, I found a 1968 Spares manual online. Unfortunately, the Lightning calls for 2.5 slides! Is this a show-stopper?

As Gavin stated, use the specs for 69/70. The 68 would have had the 2.5 slide, 2 stroke spray tube (very important) and the needle clip in the middle position and I beleive a 2 stroke needle jet and 190 main jet which would not have been cross drilled. Whilst it would have ran ok it would run better with the later adopted settings if it had the 2t needle
Jet it would also have had the 2t needle (3 ID rings?)

Later settings are (pre oif). Oif used 200 mains, I beleive the rest are the same.
#3 slide, 106 4stroke needle jet and 2 ID ringed needle. 4t spray tube (flat top) and 180 main jets. Needle clip in top position aka pos1.

The leaner settings would allow the bike to run much cleaner and more responsive.

I’m finding a richer main jet is preferred as ethanol is becoming more prevalent, but then again my bike is no longer bone stock either.


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Originally Posted by Mark Z
[quote=kevin]
Another reason I want to convert is that the bike had more low-end grunt and a crisper idle with the Amals. The Mikunis are stronger and faster "at speed", but they're soft right off idle, presumably because they're 32mm. (Maybe that's why my clutch has lasted so long!)

More likely they were not jetted correctly at low end.


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Kevin, Mikuni can be a bit soft off idle..Do the pilot jet sizing by the usual tuning, then go one size larger....Or go flatslide....


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lol

im resisting the flatslides as long as i can. i already run 30 pilot jets in my 34 VMs, 35s actually smoke. i ran anywhere from 17.5 to 25s in the 32s i used to run.

i have two sets of resistors to run across the pickup leads in my boyers that will reduce the total spark advance by 4 or 8 degrees. when i get around to actually putting one or the other in, ill be able to run the 30 BTDC that i use for twin plugs with something closer to the original advance at idle.

i know the flat slides are better carburetters than the VMs, but im a stick in the mud. i suppose i should test them-- theyre not as expen sive as amals.

you need to post more pictures of your A10.


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I feel like I'm in a different world with my essentially stock A65. I don't think it has the "lung capacity" to support the larger bore carbs; I feel I'm compensating for that by running small slide cutaways (2.0). It ran worse with larger cutaways. The change was accompanied by needle and needle jet changes. In fact I've gone through three significantly different sets of needles and needle jets, and two different "air corrector" jets. As near as I can tell (from spark plug readings), mixture is good throughout what I can measure. I still don't think I have the right needles though; if I drop them a notch, it runs like an absolute monster over half throttle, at speed, but the low-rpm performance suffers. Raised a notch, low-end performance is satisfactory, but the bike loses its monster quality at speed. That's my preferred setting, since my go-fast days are pretty much over. I could continue my search for the perfect jet needle, but I've already spent too many days of my life jetting these carbs, and I'm still faced with the necessity to run homemade air cleaners, which do nothing to quell air turbulence. The Mikunis are fine carburetors and they've served me well for almost forty years, but this is the first time I've had some rebuilt Amals to play with....

ANYWAY... Thanks for all the helpful AMAL info; it sounds like I'm on the right track. The needle jets are square on the end, and the needles have two rings above the top groove.

BTW, I'm using K&N "cone-type" clamp-on air cleaners. I tried the Amals once before with stock "pancake-type" air cleaners, and discovered that, without side panels, they looked ridiculous.


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amals are perfectly fine. i run a 930 on a 66 A65 and have another on a 69 Tbolt. and other stuff too. i personally like mikunis because theyre so much easier for me to get right. your problem with needles appears to be that you need two tapers on the same needle, and mikunis can fix that, while amals cant.

but the point of a motorcycle is to ride it, not to treat it it as a monument to some vendor manufacturer. id run jikovs if they worked.

you clearly are sensitive to your motors performance. for people like you it doesnt matter what kind of carb you run. whatever you use, youll get it right.

just sayin


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When I acquired the Mikunis (from MAP Cycle) back in 1983, the original Monoblocs on my '67 L were clapped out, new Amals were not readily available, I didn't know about Lund's, and Mikunis were cheap ($150 for the pair, with manifold adapters). Without asking, MAP sent me VM32s, I think because that was the hot setup for British flattrackers at the time. If I had known what I know now, I would have asked for VM30s. The rest is history.

Thanks for the vote of confidence. In the vein of "what did you do to your bike today?":
[Linked Image from i.postimg.cc]
The carb body on the left is untouched. The carb body on the right was done with Brasso. The float bowl on the left was done with Mother's Mag Polish, and the float bowl on the right was done with Brasso followed by Mother's. Conclusion: Mother's is better than Brasso.


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AMAL is original , Minuki not so much

everything else is technical ... depending obviously on what you are trying to achieve


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Kevin. Do you have a lighting and a Thunderbolt? Im after a seat of the pants comparison between the 2 for low end to midrange performance. Not interested in top end as i will be using it on 1/4 lose speedway tracks, i like the idea of one carb and simplicity, but also looking for low end performance.

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no both of mine are Tbolts. i dont have a lot of experience with single carb motors. theyre certainly easy to set an idle on, but other than that i cant compare.


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In my experience there's not a huge difference until you approach 5k rpms. Assuming stock gearing and equal states of tune. Above 5k a big difference.


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In my experience there's not a huge difference until you approach 5k rpms. Assuming stock gearing and porting and equal states of tune. Above 5k a big difference.

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Originally Posted by Allan G
Oif used 200 mains, I beleive the rest are the same.
.
My '71 had 200 mains when I bought it. Those proved to be too large, stock air filters, but different exhaust.
I ran VM 32's for most of the time I had the bike. Gas mileage dropped from 45 to 35 MPG, and I got very tired of rejetting to try to get the mileage up. The VM is a large instrument, as mentioned it's difficult to mount and find air filters. Unless you can find a 4-way fuel line adapter you must turn on both petcocks and have no reserve (90 degree aftermarket petcocks are required for clearance.) I guess they can work, but I cant recommend them. I was really looking for some Mk2 Amals when I bought the Miks.
Later I found a set of new Concentric bodies and reverted to them. The bike was running quite well when I sold it.


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Originally Posted by DavidP
Originally Posted by Allan G
Oif used 200 mains, I beleive the rest are the same.
.
My '71 had 200 mains when I bought it. Those proved to be too large, stock air filters, but different exhaust.
I ran VM 32's for most of the time I had the bike. Gas mileage dropped from 45 to 35 MPG, and I got very tired of rejetting to try to get the mileage up. The VM is a large instrument, as mentioned it's difficult to mount and find air filters. Unless you can find a 4-way fuel line adapter you must turn on both petcocks and have no reserve (90 degree aftermarket petcocks are required for clearance.) I guess they can work, but I cant recommend them. I was really looking for some Mk2 Amals when I bought the Miks.
Later I found a set of new Concentric bodies and reverted to them. The bike was running quite well when I sold it.

Its funny with the twin carb bikes that the main jets for both Lightning and Firebird models changed for the OIF. For the Thunderbolt, carb settings remained the same.


Now let’s all have a beer beerchug

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Bacon gives for the Lightning 30mm carb main jet:
'68 190
'69/'70 180
'71/'72 200

The Thunderbolt 28mm carb main jet:
'68 230
'69/'72 230

The '68 Hornet and '69/'70 Firebird had the same mains as the Lightning but the '71 Firebird Scrambler have 220 mains.
Possibly the '71/'72 Lighting had larger mains to reduce warranty claims due to more WOT riding.

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Originally Posted by DavidP
Originally Posted by Allan G
Oif used 200 mains, I beleive the rest are the same.
.
My '71 had 200 mains when I bought it. Those proved to be too large, stock air filters, but different exhaust.
I ran VM 32's for most of the time I had the bike. Gas mileage dropped from 45 to 35 MPG, and I got very tired of rejetting to try to get the mileage up. The VM is a large instrument, as mentioned it's difficult to mount and find air filters. Unless you can find a 4-way fuel line adapter you must turn on both petcocks and have no reserve (90 degree aftermarket petcocks are required for clearance.) I guess they can work, but I cant recommend them. I was really looking for some Mk2 Amals when I bought the Miks.
Later I found a set of new Concentric bodies and reverted to them. The bike was running quite well when I sold it.

Interesting David, how we've followed the same path for such a long time (except for your abandoning your A65!). Although I must admit, my devotion to my A65 is waning a bit since I've acquired my 2007 Bonneville Black, a marvelous machine, and now my main ride. I recently did a "hone and ring" job on the A65, leaving the piston clearance at .006-.0065". Now the engine is noisier and vibrates more than before. Indications are I may have to bore it to +.060, and this time I should probably check out the lower end. And a re-bore will necessitate crank balancing again. Unfortunately, the mechanic who has done my last three A65 lowers has died. All in all, I'm not sure I have the gumption to go all through this once again.

But I can ride the A65 a while longer, saving it for "special events" (shows, swap meets, etc.) and an occasional romp around the 'hood, and I can see how it runs with the Amals.


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Originally Posted by DMadigan
Bacon gives for the Lightning 30mm carb main jet:
'68 190
'69/'70 180
'71/'72 200

The Thunderbolt 28mm carb main jet:
'68 230
'69/'72 230

The '68 Hornet and '69/'70 Firebird had the same mains as the Lightning but the '71 Firebird Scrambler have 220 mains.
Possibly the '71/'72 Lighting had larger mains to reduce warranty claims due to more WOT riding.

Thanks, and this agrees with Alan's and Phil's direct experience. I think I'm good to go.

This polishing is just with fingers and rags. I could probably do more with Dremel tools, but three evenings of polishing is enough - not necessarily museum quality, but respectable. Time to put them together.
[Linked Image from i.postimg.cc]


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The only thing I would worry about with shiny carbs is its ability to disipate heat... though they don't look "polished" so will likely be ok.

Like David P, with pre-oif silencers I found anything bigger than a 180 to be too big, didn't have much detriment on the running but it ran its fastest at WOT with the 180. Since then fuels have changed slightly and to be honest so have my bikes somewhat and im finding bigger main jets suit my bikes running. Though with non standard cams I wouldn't take that as gospal for anyone elses bike.

Dave M could be right about the warranty claims, I have yet to try anything different. I think the 69 on Firebirds with the 1 3/8" pipes make much higher BHP and torque at a higher RPM??


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You were right NickL in stating that the Mikunis "look crap".
[Linked Image from i.postimg.cc]
I haven't started the bike yet. The right carburetor is overflowing. The shutoff needles are new, so it probably just needs cleaning. Flushing it with the drain plug out didn't fix it, so I'll have to drop the float bowl.


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I got the right side carburetor to stop overflowing tonight and ready for startup tomorrow. I cleaned the shutoff needle and seat with WD-40, although there was no visible dirt there. Then I noticed a bit of dirt inside the hollow fuel banjo bolt - I almost missed that, and that could have been the source of the problem. Anyway, it's fixed now.

On a side note, a quarter, or better yet, a washer just a bit thicker than a quarter, fits nicely into the slot in the plastic float bowl drain plug, and IME is the only tool that should be used to loosen and tighten the plug. Just mentioning this because I've seen too many drain plugs chewed up from using channel locks on them.


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Hi Mark, .When it comes to setting idle mix, blank off the inlet balance pipe, so the RHS doesnt mess with the LHS ,and visa versa, makes dialling the idle mix much easier, reconnect when done.


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Originally Posted by Mark Z
On a side note, a quarter, or better yet, a washer just a bit thicker than a quarter, fits nicely into the slot in the plastic float bowl drain plug, and IME is the only tool that should be used to loosen and tighten the plug. Just mentioning this because I've seen too many drain plugs chewed up from using channel locks on them.

i think its sized for a half crown.


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Originally Posted by gavin eisler
Hi Mark, .When it comes to setting idle mix, blank off the inlet balance pipe, so the RHS doesnt mess with the LHS ,and visa versa, makes dialling the idle mix much easier, reconnect when done.

Bigger fish to fry right now - they won't idle, I mean, at all. They have all the signs of clogged idle passage, have to tickle and give it throttle to start every time, even warm, mixture screws set to 3/4 turns out, runs great as long as I stay on the throttle, if I let go of the throttle for even a second and then rev it, it almost dies and then catches - any longer than that and it dies, period.

I tried cleaning out the (fixed) pilot jets with my torch tip cleaner, to no avail. Maybe swarf behind the pilot jet, how the heck do you get that out of there? I guess I should try a tiny drill bit before I remove and soak them in Chem Dip. Anyone know the drill size? I think I figured out once it's .016-.017" diam., I could bring my calipers to the store?


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on a Mikuni you can take out the pilot jet and see daylight through the immense hole that remains. easy to clean, no mixing chamber for mung to clog up . . . just sayin

try turning the air screws 1-1/2 turns out and see whether that changes anything.


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Drill size #78, essential tool.


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The welch plug and the 2x passages often get blocked meaning that no matter how clean the pilot jet is… it still won’t run right. Get some carb cleaner spray, remove the pilot air screw and insert the straw from the carb cleaner. Look down the threat of the carb and with the throttle open or slides removed. Spray!!! You should see 2 good streams squirt from the holes. Until it’s does that the idle circuit won’t work properly.

The one engine side of the slide is the pilot circuit. The one under the slide allows transition between the pilot half of the carb and the main Venturi. Which is why I think sometimes a bike will idle ok but then cut out when you open the slide (providing those carb settings worked fine previously)


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Originally Posted by kevin
on a mikuni you can take out the pilot jet and see daylight through the immense hole that remains. easy to clean, no mixing chamber for mung to clog up . . . just sayin.
Now now Kevin, I'm painfully aware of what I'm giving up here.
Originally Posted by kevin
try turning the air screws 1-1/2 turns out and see whether that changes anything.
Ran "best" (if you can call it that) with the air screws at 3/4 turns out. Another indication of a clogged pilot circuit.

Allan, thanks for a thorough description of the pilot circuit. I'm off to the store for a #78 drill bit - already have some spray carb cleaner (and a face shield!).


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Originally Posted by Mark Z
Originally Posted by kevin
try turning the air screws 1-1/2 turns out and see whether that changes anything.
Ran "best" (if you can call it that) with the air screws at 3/4 turns out. Another indication of a clogged pilot circuit.

Allan, thanks for a thorough description of the pilot circuit. I'm off to the store for a #78 drill bit - already have some spray carb cleaner (and a face shield!).

if it runs best with only half the air going in the past the airscrew, then i imagine youre right that the pilot system isnt passing enough fuel. you may find it difficult to buy a 78 at any ordinary source-- hardware and auto parts stores will have only much larger bits, around 1 or 2 millinmeters. you may find that hobby stores that cater to model builders or electric train people will have something on the shelf. failing that, ebay sells them.

https://www.ebay.com/itm/312994898373?hash=item48dff321c5:g:4FsAAOSwrrleRubT&amdata=enc%3AAQAHAAAA4Hq8lOrRKzoRPTAKrJBkUroEVSZQoexBgUYVUKTx4Vk2Kn5F7fB2S1hnt5Eds8eRCh8qVpa1PlPR0sx6WVCPh%2By%2FGLjy0ecN14CHoBH2c65Wp3j3n32jiHbBZMlYGSx80lAEPWmgL9kIK5YVJsGhqHOYQSoWZzFdhobYATtHq192tZIfOUU39fe%2FOkp%2BkgT8U1EV%2BQDOv21ogCvz1PwhKBvmPcfhTybEOqD0JdwqCKXSXpv%2BA4wUiJIw4unP%2F4s27omnGuAwdlg%2BJEhMwF2EDQT2HIWIDfBKJD6%2BMwub3DTW%7Ctkp%3ABk9SR_7uy5_qYA

but im not against amals. im in the process of trying to get my 441 to run as we speak

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Right you are Kevin, the smallest bit they had at the hardware store was a #60. I don't think I mentioned this earlier, but my torch tip cleaners are smooth for about 1 centimeter at the end, and there are no burrs or sharp edges, so I'll continue with those (the right one, that is, which is .017"), and try the carb cleaner flush.

But first I have to get them off (which is a bit more involved than the spigot-mounted Mikunis), and I have to go back to work tomorrow.


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If you cannot find a 0.016" (#78) drill (McMaster has them) bit you can use music wire from a guitar store. A little handier since they can reach the bottom of the slide floor. Drils are only 7/8" unless you get an extended length 1-1/2".

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Using adhesive bond the #78 drill into a WD40 flexible "straw".
#78 is 0.016" so if you use a 0.017" tip cleaner you will have an oversize pilot jet.
A 17 thou hole compared with a 16 thou hole has 13% larger cross sectional area so if you use a 17 thou tip cleaner you will f**k up your [pilot jet.
When using the #78 drill then twist the drill bit so that you drill all of the crap out of the hole.
The crap is tenacious and needs actually drilling out.
Think of it as a solid wall that you need to drill through.
Just my two cents worth of course.

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Tridentman, I got the carbs off the bike tonight and explored further with the torch tip cleaners. You are right, the .017" cleaner does not fit into the jet. The next smaller size is .014", which does fit. But I'll start checking out local hobby shops for that #78 bit.

What still troubles me is that long passage from the pickup hole (where the removable pilot jet was on earlier carbs) to the main jet. There's no way to get in there with any sort of tool, so I think soaking and compressed air may be required.


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There is a "Welch " plug in the roof of the float chamber, if you have a spare welch plug, you can remove the old one by drilling a wee hole in the middle , screw in a self tapper and pull the plug, beneath it you will have access to the mung pit/ pilot mix chamber . I have cheaped out before and refitted the drilled plug with a dab of epoxy, now have spares, Burlen sell them, should come in the rebuild kits. In the roof of the mix chamber you can see the bottom of the venturi delivery jets, at the side and rear you have access to air and fuel drillings. Since I got some #78 drills I no longer bother opening this up, somethings are best left unseen.

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Originally Posted by Tridentman
Using adhesive bond the #78 drill into a WD40 flexible "straw".
#78 is 0.016" so if you use a 0.017" tip cleaner you will have an oversize pilot jet.
A 17 thou hole compared with a 16 thou hole has 13% larger cross sectional area so if you use a 17 thou tip cleaner you will f**k up your [pilot jet.
When using the #78 drill then twist the drill bit so that you drill all of the crap out of the hole.
The crap is tenacious and needs actually drilling out.
Think of it as a solid wall that you need to drill through.
Just my two cents worth of course.

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You should be able to get #78 drill bits from any good engineering supply store.
That is where I get mine-- I think I got 10 for about $12---but that was several years ago.
If you want to really hit the problem on the head then drill out the plug opposite the pilot jet and tap it 2BA.
Then take any old pilot jet, cut off the end and use the part with the screw head to blank off the port.
Then you can take out the plug every time you have a problem and really get it clean.
If you dont want to do that then use the #78 drill and use an aerosol of carb cleaner to flush out the ports with some force.
Do it several times and eventually you get it clean.
Best of luck!

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Ok, so I soaked the carb bodies in Berryman's, triple rinsed them in water, and blew them dry with compressed air.

Now, on one carb, I can get carb cleaner to squirt out the two tiny holes in the venturi by pumping it in into the air mixture screw hole. I can also get carb cleaner to squirt out those two tiny holes by pumping it into the fuel pickup hole in the ceiling of the float chamber.

On the other carb, I can get carb cleaner to squirt out the two tiny holes in the venturi ONLY by pumping it into the air mixture screw hole. That is to say, I can't get the carb cleaner to squirt out anywhere by pumping it into the fuel pickup hole.

That tells me, on carb #2, the blockage is between the fuel pickup hole and the pilot jet. I guess that means the welch plug will have to come out.

I've never removed a welch plug before; I believe the process cited above was to drill a hole in it, insert a self-tapping screw, and pull. How hard are these things to get out? Also, will the hole vacated by the plug be on the feed side of the pilot jet?

Tridentman, I will also consider your idea of drilling and tapping the plug opposite the air mixture screw, but removing the welch plug sounds like less work, if it comes out relatively easy.


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Originally Posted by Mark Z
Ok, so I soaked the carb bodies in Berryman's, triple rinsed them in water, and blew them dry with compressed air.

Now, on one carb, I can get carb cleaner to squirt out the two tiny holes in the venturi by pumping it in into the air mixture screw hole. I can also get carb cleaner to squirt out those two tiny holes by pumping it into the fuel pickup hole in the ceiling of the float chamber.

On the other carb, I can get carb cleaner to squirt out the two tiny holes in the venturi ONLY by pumping it into the air mixture screw hole. That is to say, I can't get the carb cleaner to squirt out anywhere by pumping it into the fuel pickup hole.

That tells me, on carb #2, the blockage is between the fuel pickup hole and the pilot jet. I guess that means the welch plug will have to come out.

I've never removed a welch plug before; I believe the process cited above was to drill a hole in it, insert a self-tapping screw, and pull. How hard are these things to get out? Also, will the hole vacated by the plug be on the feed side of the pilot jet?

Tridentman, I will also consider your idea of drilling and tapping the plug opposite the air mixture screw, but removing the welch plug sounds like less work, if it comes out relatively easy.

Before you remove it, see if you can find someone with a sonic bath, put some of your berrymens solution in that. WD40 seems to break down fuel quite well also.

The welch pool itself cannot be blocked if both transfer ports flow when sprayed from the air bleed side. So the issue I believe still remains in the pilot jet.

Also try not rinsing the carbs out with water. Water has a higher viscosity and density than fuel has. If you want to clean out the berrymans, stick with a carb cleaner, brake cleaner or acetone which will disperse the water and evaporate.


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Allan, it sounds like you're saying that the welch pool is downstream (with respect to the fuel) from the pilot jet. And yes, that means removing it will accomplish nothing.

It also occurs to me that spraying carb cleaner into the air mixture screw hole is not a valid test for the pilot jet or the feed side of the pilot jet, unless I can see carb cleaner come out the fuel pickup hole, which it is not. (It IS on the other carb.) I believe the pilot jet itself is clear, and the problem is in the passage between the pilot jet and the fuel pickup hole in the ceiling of the float chamber.

Now, drilling out the plug opposite the air mixture screw as Tridentman suggested would provide access to the feed side of the pilot jet, but I will try some more soaking and/or flushing first.

It seems that, after soaking in the Berryman's, dropping the entire basket into a bucket of water is the only way to safely handle the parts. After that, I can continue to flush with carb cleaner or WD-40.


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have you tried compressed air?

you cant hurt anything with air pressure, and it can loosen stuff that a spray can will not.


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Welch Plug listings on Burlens page https://amalcarb.co.uk/catalogsearch/result/?q=welch+
Not sure what the correct plug is for the 900 series carbs, possibly the listing with 9 as the first digit?
I spoke to Burlen on the phone when I got spares. Sadly these are not shown on the AMAL / Burlen exploded diagram.

The passage from the fuel pick up to the mix chamber has two 90 degree bends, poke with flexible wire/ monofilament , soak in vinegar and blast with compressed air. I boiled my carb bodies in Rhubarb leave juice ( dilute oxalic acid) that seemed to clean the internals well.
Pulling the welch plug will allow access to each end of the passage.
50lbs breaking strain fishing line is flexible/ stiff enough to probe passages with some finagling.
Best tool for the job would be an ultrasonic bath .

Last edited by gavin eisler; 09/24/22 6:40 pm. Reason: splingel

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Originally Posted by kevin
have you tried compressed air?

you cant hurt anything with air pressure, and it can loosen stuff that a spray can will not.

Yes, I failed to mention that. I did use compressed air to blow out the Berryman's (after rinsing in water). I did not use compressed air after spraying with the carb cleaner, but I will this time.

It seems I will want to blow into the air mixture screw hole (as opposed to the fuel pickup hole), so as not to just blow the sh*t back into the pilot jet. I may want to first poke out the pilot jet again.


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Went back at the carbs today - WD-40, compressed air, then carb cleaner, compressed air. Covered holes as required.

I think the carbs are good to go now; carb cleaner squirts freely out all the right orifices, blew them out one more time. I'm at least confident enough to put them back together and do a test run.

I might mention that these carbs were not grungy. I took them off a running bike and drained them before putting them on the shelf. They were disassembled, of course, for the trip to Lund's, then bagged, boxed, and stored for the duration.

Question, is it kosher to smear a little grease on the float bowl gaskets? I don't usually put anything on them, but this time I'm reusing gaskets. They're essentially brand new, but they've been removed and reinstalled a couple of times now.


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Great news Mark!

I never fit anything to mine. Just dont over tighten them, if they dont tighten sufficiently, consider a new gasket.


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I always put the barest smear of grease on these gaskets.
Put a dab of grease on both sides, wipe most of it off with your finger.
Belt and braces I guess--- but i have not had a leak at this point since Adam was a lad.
HTh

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With carbs back together and mounted, I started the engine tonight. Same problem, still won't idle. Requires tickling the carbs to restart, every time.

I'm reasonably sure the idle circuits are clear now, so I have a new theory, and that would be that the floats are set too low. The bike actually idles for three or four seconds after letting go of the throttle before it slows down and dies, as if it were running out of fuel. Can low floats produce this symptom?

I've never paid much attention to float level, and I've forgotten the specification. I've also never had to move a float needle seat, and I'm worried about damaging the seat. I'm also wondering how one goes about moving the seat without moving it too far.

(Side note: I've concluded that using stop nuts on the mounting studs is positively masochistic, since you can only get an open-end wrench on them, and only turn them one flat at a time. I went through my parts cache and dug out original nuts, and cleaned the studs to the point where I can spin the nuts on with my fingers.)


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If you get a spare float bowl plug you can make a tool with a fitting on the bottom and a piece of clear tubing. Then you can check the actual fuel level. There are many here who could say where that should be.

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Check the float bowl mating surfaces are flat, they get bowed easily, this creates an air leak and prevents the uptake of the pilot fuel which has to pass through the gasket/ joint. This gets worse as the fuel level drops.


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Mark, you never mentioned what speed you were setting the idle to. Hopefully, not a barely tick-over but 900-1000 RPM.
Will it continue to idle with the choke full or partially on?
The float lever can be changed by using a flat nose punch and tapping the seat up or down in the bowl.
The gasket has to have a good seal around the diagonally drilled hole in the bowl which feeds fuel to the idle circuit as Gavin mentioned.

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The float bowl and carburetor mating surfaces appear to be clean and in very good condition, and the gaskets are new, except for the few times I've removed the float bowls as part of this exercise. On this last assembly, the gaskets received a very thin smear of grease.

DM, I had the idle speed set abnormally high in an effort to keep the engine running. No chokes, and the holes for the choke cables are plugged with screws. After last night's session, I thought about trying to flood the carbs while it was running, but this is rather difficult to do, especially on both carbs at the same time, before the engine dies. I may still try that before taking them apart again.

I didn't initially check float levels because these carbs worked ok on the T140 I took them from, except for the fact that the slides and upper tubes were worn, which was subsequently addressed by Lund's Machine. I may have changed shut-off needles, changing from plastic to Viton-tipped metal. Anyway, I'll check them out. I just remembered, I have the factory documentation that came with the NEW carbs for the T140, and another pamphlet on tuning AMAL Concentrics.

I was under the impression that you have to heat the float bowl before trying to move the shut-off needle seat. Not true?


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You’re in a bad way if the float seat moves without warming up the bowl. I find the new bowls are virtually impossible to move the seat.


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Does it idle when the engine is warm? I would check that before pulling the carbs again.
Heating the bowl makes moving the seat easier. The punch should be the largest that will fit with a smooth flat face.

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Originally Posted by DMadigan
......Heating the bowl makes moving the seat easier. The punch should be the largest that will fit with a smooth flat face.
Or, you just slap the heated float bowl gasket face down hard on a flat steel surface, like a drill press table. Wear gloves of course, and do it a few times until the seat moves out a little. Check your float level quickly while it is still hot and tap the seat back in if needed to fine tune the level. I've done it that way for years.

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