Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board A65 62 - works bad cold - need hlelp

Hi ! i'm trying to resolve a problem on my 62' A65

single Monobloc carb, Boyer digital (red box), dual Boyer ignition coil

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. Thought it was ignition problem, changed spark plugs, connectors, tried another coil, and another Boyer box i had, the problem stays exactly the same. Cleaned the carb (fully opened it and cleaned it all), same problem ....

Any idea ?

Sounds like a pilot blockage or an air leak, is the slide worn badly? O- ring in the manifold perished? O- ring on the air screw can perish badly. I would try a different carb that is known to run well, old carbs at that kind of mileage can be problematic.

Why do you think the points cover would change something here ?

The slide moves freely, i checked it when i cleaned the carb, and i clearly hear it moving up and down - i also checked the move before putting back the air filter, and it moved perfectly from full closed to full open and back with no blocking point ... i may search for an air leak, the main O ring is in place and looks good, but i didn't chek for the o ring on the air screw ....

PEH, from what i see on schematics, there is no o ring or seal on the air screw on the Monobloc carb ....

Pilot air bleed clogged? Sounds like the Concentric problem if Monoblocs do the same thing….

Wow!! “ It was runing nice, did 40 thousands miles with no big problem” Is that possible ???? 😳

Sure it's possible. Did 2 complete check, with engine strip down, no major problems found. Some minor worries time to time, but always found a way to repair and get back home. It's the first time i can't find how to fix it ....

Unless the screws were 3” long, the cover would have no effect at all on an A65.



You’re running a Boyer micro digital… first thing I would look at/charge or change is the battery.

Sounds like the charging system is topping the battery up the more it is running but maybe a cell has gone down or it has been stored a little while with a partially discharged battery.

Electronic ignitions are very susceptible to battery issues. Infact when having an electronic ignition, most “seemingly carb problems” are infact electrical problems… more often than not the battery.

Pureblood, in the OPs first post he states he has EI not points.Nothing out of ten for reading comprehension.

+1 for what Allan said, check your battery voltage, before starting, then when running. Sounds like a bad battery to me.
Equally possible , there may be a dodgy connection somewhere between battery and Boyer, a jumper wire will prove this one way or another.

sometimes the whole jet block in the carb or just the jets can come loose ... easy thing to check

Forgot to say at the beginning : the battery is perfect and fully charged, no worries about this - anyway, the digital Boyer works perfectly at 10v (that’s why i put the digital Boyer, the black ones misfires and changes the advance under 12v)

Two thoughts come to mind.....

1) compression, ....... busted ring?? ...... but then it would probably be hard to start, but perhaps not if on only one pot. Feel the exhaust, you will soon see if the issue / misfire is with both cylinders

2) Forget the battery, ... how many volts does the Boyer actually GET? (as suspected by Gavin)

I got 13,4V on the battery, no problem here - i ordered a compression tester, i'll check the compressions when i get it (ring or valve problem ?) i'll check the voltage directly on the Boyer connectors, just in case of a faulty cable ...

If I’ve learned anything this year it’s that voltage only tells you part of the battery story.

Much smarter people than me ( you know who you are) taught me about “load testing”. I don’t remember right now (nothing unusual for me) but I think I had 6 batteries in the shop that all showed good voltage. Purchased a load tester…..threw 3 of those batteries away.

Mr Healy says “You don’t need a new battery, you need a good battery”

Unless you load test it……you don’t know what you have.

Damnit…….give the boy (me) a little knowledge and he starts acting like an expert!!!

I've had batteries going dead, the voltage was going down and the horn was low, as the lights .... and the bike was still running well with a little rev ... the actual battery is in perfect condition, fully charged, horn is loud and lights are bright ...

don't know about this "load test", sounds like a marketing invention for me ^_^

On a bike with a Boyer?

All a man can do is try to help…..can’t make someone actually listen. Yea, load testing a battery is simply a marketing invention

That said…..I had a Commando that the valve springs were bad/weak. Ran like a pig until it warmed up.

As i said before, the Boyer digital (red box) works very well with low voltage. At 10v it works perfectly. Not as the old ones (black box) that begin to fail under 12,3 v ....

Its not the voltage when not in use but its ability to supply a even current when under load. Look up Volts-Ohms-Amps



You could have a battery which works fine when you put a meter across it and the bike not running, but start using the bike and it runs poor. maybe it will get better as the bike runs on and the battery slowly accepts charge. (I have had this) with a high output alternator I have gotten away with it for some time but eventually the battery just says see-ya!

With mine, I fitted a capacitor in parallel to the battery for a period of time and that showed a huge improvement in the bikes running (it always ran ok before hand). In the end I found my problem lied with my regulator, despite charging the battery the bike ran like crap. I then fitted the MOSFET Trispark reg-rec and its ran really good with just that and the battery and didn't refit the capacitor.


You could also connect the white wire from the Boyer straight to the battery and add an aditional red wire from the battery to the +VE side of the (2nd if you have two fitted) coil which is where the red wire from the Boyer box also meets. - this will rule out any wiring gremlins (as per the funny picture).

I already put a mosfet regulator (Schindengen) because all the electronic regulators we find are crap. When a battery gets poor when running, the voltage lowers ... in my case the voltage is around 14v when running, and 13V whith lights on ... we discuss a long time about battery charging, but it's obviously not the problem here ....

With the engine not running switch on the headlight and leave it on for two minutes.
See if the headlight brightness reduces in that time.
If it does your battery is crap.
This is called a load test and doesn't cost you a cent (or even a euro).

it doesn't reduce, as i said, my battery is fully operationnal, i can let the light on 15 minutes, it won't reduce .... But if anyone here is interrested in batteries problems, he can create a new topic about battery load tests ....


ps : for the record, i did this 2 mn test - at start, battery was 13.4V - after 2mn of bright light, it went to 13.2V - and the light was still bright ....

Good-- you have just conducted a battery load test.
Didn't feel like a slick marketing con trick did it?
Based on your result I would agree with you that the battery is not your problem.
Having established that your battery is good you now need to make sure that its volts get to where you want them to get to.
Check all the connections from the battery---both on the supply side and the earthing side.
Dont just measure volts-- tug on the connections while measuring volts--often the volts are expected to get through just one strand of wire.
Best of luck!

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.

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 ....

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)