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Originally Posted by Rokplo
Hi ! i'm trying to resolve a problem on my 62' A65

It was runing nice, did 40 thousands miles with no big problem.

But suddenly it's running bad at start (coughing, need to rev it high, harsh sound) but after 5/10mn running (maintaining high revs to avoid stalling) it runs better, and after 5mn more it runs ok. .........
Have you checked valve clearances? If they are tight, that could be the trouble. Also, high mileage BSA's can carbon up the valve stems so the valves stick which could also cause your problems. It sounds like most everything else is ok from what I've read in the thread.

It makes me think of a Honda F4I 600 project bike I had some years back. According to the seller, it would only start sometimes and he had given up on it. It turns out it had negative valve clearance on several valves (Valves being held open). I corrected the clearances and the bike fired right up and purred like a kitten. I never heard it run with the tight valves but I imagine it would have sounded like a 4 cylinder version of your BSA until it warmed up.

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Stuart it's a possibility, i ordered a compression tester, it will tell me if compression is ok ...

if it is, no problem of valve or rings ...

if there is a compression problem, i'll check valve clearance, and if valve clearance is ok, i'll have to open the head to check what's going on here ....

Il also ordered gaskets for the carb, i'll put new ones everywhere i can, to avoid a potential air leak.

I also heard of valve getting a little bit stuck in the guide when cold, and become free with heat, because of a bit of dirt stuck somewhere ....


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Tridentman, if there was a wire problem, it wouldn't become good with heat (or it would be the first time i hear about this)


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Originally Posted by Rokplo
…..snip…..
I also heard of valve getting a little bit stuck in the guide when cold, and become free with heat, because of a bit of dirt stuck somewhere ....

It was along time ago but I had a Commando that would run like a pig until it warmed up……then was fine. I have no recollection of how I found out what the problem was but it turned out to be weak ( not broken) valve springs. Swapped out for new and the problem went away.

Just trying to help


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Originally Posted by Gordon Gray
Originally Posted by Rokplo
…..snip…..
I also heard of valve getting a little bit stuck in the guide when cold, and become free with heat, because of a bit of dirt stuck somewhere ....

It was along time ago but I had a Commando that would run like a pig until it warmed up……then was fine. I have no recollection of how I found out what the problem was but it turned out to be weak ( not broken) valve springs. Swapped out for new and the problem went away.

Just trying to help


Thanx, i'll have a look if i have to open the rockers cover ....


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Someone had to have told me about that being a possible problem…..honestly I wouldn’t have known to look at/check them.

I think it was one of those things where I actually got the new springs first figuring new springs wouldn’t be a bad idea.

The bike would start but REALLY stumble until warmed up then it ran okay.

I only paid $325 for it so it got a lot of worn out stuff replaced.

Good luck……keep at it, you’ll sort it


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This may have been covered disregard if it has.

How’s the carb slide, ever been sleeved.
Not sure if you checked vacuum leaks. I use WD 40 sprayed around the flange. If it revs you got a leak, be carful.
How’s the plugs looking on a cold run, before it smooths out. ie: crappy running may be lean do to sloppy slides or vacuum leak.

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Originally Posted by Richard Phillips
This may have been covered disregard if it has.

How’s the carb slide, ever been sleeved.
Not sure if you checked vacuum leaks. I use WD 40 sprayed around the flange. If it revs you got a leak, be carful.
How’s the plugs looking on a cold run, before it smooths out. ie: crappy running may be lean do to sloppy slides or vacuum leak.


Slide seems ok, il check for air leaks, i ordered a set of new seals and gaskets, i'll renew it all to be sure


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Carb clean, brake clean or easy start would show an increase in revs when sprayed around a leaking flange. WD40 isn’t very combustible and usually causes engine revs to falter.


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Have you felt the exhausts like I mentioned earlier?
Sometimes it is hard to tell if a problem is on both cylinders or just one.
You may not feel any difference, but if you do then you can eliminate a load of common factors, like carb, ignition etc.
Probably need two people.
Just spent a length of time messing with a Chinese copy of a 1990s Honda. Previous hackers had installed new carbs plus a ton of stuff, missing the fact it wasn't firing with any gusto if at all on one pot! Still haven't fixed the problem (and probably won't) but at least I know what it is!

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This morning, before going to work, i checked valve clearance. Left inlet valve had not enough clearance (0.10 mm instead fo 20). My carb is in pieces, waiting for new gaskets and seals, so i couldn't try yet. Hope it's only that ....

I'll receive my compression tester today, so i'll check compressions tonight


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I finally rebuilt the (cleaned) carb with the old gaskets .... exactly the same thing, no change at all .... i also put (again) new spark plugs, and checked it after 3 mn reving up : perfectly clean as new, no gas wet or oil on it

Last edited by Rokplo; 09/22/22 9:18 am. Reason: orthograph

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Just mesured compressions : 7bars/100 psi in each side, coherent with the 7.25 :1 compression ratio ... still thinking it’s a carb problem ...


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Quoting the WSM, "7.5:1 CR, Comp pressure, both plugs out, throttle open, warm motor, first kick 65-70, Average, 120 -125 psi.
If readings obtained are substantially below those quoted, the engine is need of attention to valves, and piston rings or may even require a rebore"


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Originally Posted by gavin eisler
Quoting the WSM, "7.5:1 CR, Comp pressure, both plugs out, throttle open, warm motor, first kick 65-70, Average, 120 -125 psi.
If readings obtained are substantially below those quoted, the engine is need of attention to valves, and piston rings or may even require a rebore"


I did mesurements on cold engine, first kick was 100 ....

Last edited by Rokplo; 09/23/22 9:31 am.

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Originally Posted by Rokplo
This morning, before going to work, i checked valve clearance. Left inlet valve had not enough clearance (0.10 mm instead fo 20). My carb is in pieces, waiting for new gaskets and seals, so i couldn't try yet. Hope it's only that ....

I'll receive my compression tester today, so i'll check compressions tonight

at 0.004" inlet clearance it will run like a pig until doing a high RPM. I tried tightening up my inlet valve clearances by a couple of thou once upon a time. completely altered how the bike ran, and it wasn't very tractable compared to standard settings.


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Simple easy way to eliminate the possible wiring / connections. Attach a jumper direct from battery to the Boyer, try running. Then do the same with the other “side”, try running. (Not sure if you are set up + or - to frame)
BTW, This is how I found the loose lug rivet on the IGN switch was my issue. (Only jiggled when running)


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Originally Posted by KC in S.B.
Simple easy way to eliminate the possible wiring / connections. Attach a jumper direct from battery to the Boyer, try running. Then do the same with the other “side”, try running. (Not sure if you are set up + or - to frame)
BTW, This is how I found the loose lug rivet on the IGN switch was my issue. (Only jiggled when running)


Yes, good idea, i'll make a very simplified wiring with just Boyer, battery and coils, it will eliminate the electrical possibility (or confirm ?)

Last edited by Rokplo; 09/23/22 2:57 pm.

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