1962 A50 LEAN ONE CYLINDER

[nourydr12]

HI all-  Interested in any feedback. Pretty much done with an A50 I picked up awhile ago, or as far as i'm gonna take it. Its a good bike, original frame and engine and 85 % of parts. Starts first kick and runs well with great compression in each cylinder. Problem is….. It is running lean on the left cylinder only? It is a single carb with 2 inti 1 manifold. My first thought was rocker arm clearance. The exhaust valve is a little tight so most of the gas is being vaccumed out before combustion. Adjusted all valve clearance and still lean.?
My next thought, carb..
ANY THOUGHTS

Thanks
Bob

[mark2]

try angling the carb towards the lean cylinder so bias , I had to do this on a triumph

[murdo]

Intake gasket? Had a Triumph Daytona 500 with right cylinder running lean, checked valves, plugs, compression test, cleaned carb and found a bit of the gasket missing underneath the manifold. New gasket and all good again.

[nourydr12]

Hmmm- Ok two good thoughts. I was heading into carb next. thought the needle jet may be buggered up and spraying off to one side.
Thanks
bob

[john.k]

It could also be in the exhaust sytem,one side more restrictive than the other.Two separate pipes or 2 into 1? Similar looking but mismatched mufflers.On the intake side check for   leaks,also worn inlet valve guide on one side, and look into the manifold inside and see if the casting is off to one side. .Im not sure what you mean about tight valve and vacuuming?A sticky valve will cause a misfire and maybe banging in the exhaust.Regards John.

[nourydr12]

I JUST PUT NEW STOCK SILENCERS ON. THE EXHAUST IS FREE AND CLEAR.
I'VE HAD 2 STROKES FROM THE EARLY SIXTIES WHERE THE EXHAUST BECOMES PLUGGED FROM UNBURNED MIXTURE, AND IN FACT IT WAS COMMON PRACTICE TO REMOVE YOUR EXHAUST EVRY MONTH AND SOAK IT IN KERO… BUT THATS NOT THE PROBLEM HERE
THANKS THO

[JFerg]

This is an oldie, plainly forgotten by many.  A common "defect" of single carb parallel twins regardless of make.

How do you define "running lean"?  One spark plug darker than the other?  If so, it will be the timing side plug that is darker.  The oil feed into the timing side mainshaft delivers oil at higher pressure to the first big end that it gets to, which means that the timing side will always burn more oil than the drive side.  Not enough to matter, but enough to colour the plug.

JFergf

[iansoady]

You used to be able to get an angled spacers for A10s as they suffered a similar problem. May be worth looking for one.