Twin carb head, right cylinder misses badly

[BSAs4ever]

Hello to all - I'm new to this site, but look forward to finding answers to many puzzling BSA-related questions I have as well as providing any help I can to answering others concerns - - -

I restored a 1963 RGS that I bought as a barn find and it has come together very nicely.  It is unique in that it has a twin carb head & twin carbs.  However, I am having difficulty getting it to run properly.  The left cylinder appears to run well, but the right cylinder misses badly and isn't performing well at all.  The engine was totally overhauled by Classic Cycle Works, Georgetown, SC and has had virtually all new motor parts (valves, springs, pistons, crank bearing conversion, belt drive, etc.  The peculiar thing about the carb set-up is that the carbs are so close together that the right carb doesn't have a float, but instead is coupled to and shares the left carb float bowl with a fuel line.  From all I can tell, everything appears to be assembled properly, but I wonder if I need to follow some special tuning procedure to get the right cylinder to run as smoothly as the left.  Right now it sounds terrible as the right cylinder barely fires at all.  It seems that the right cylinder is starving for fuel & that the single float isn't properly supplying the right cylinder. 

I would love to hear from anyone who has had experience with this type of dual carb installation.  Right now they are jetted with common jet sizes, pretty much as the bike was set up when I got it.  It was not in running condition when I bought it and the original owner has since passed on.  His son did say that the bike ran very well in its earlier days. 

I did try to contact the Amal web site for their comment(s) but received no reply.  Maybe there is a simple solution?  I'm open for any suggestions that this web site's gurus may supply.  I'm so frustrated that I'm considering taking off the dual carb head and reverting to a single carb head.  (But - doesn't that seem like a shame when the dual carb installation is so cool looking & a bit of a conversation piece.  It's just something you don't see that often.

I look forward to and appreciate any response.

Cheers -
BSAs4ever
 

[chaterlea25]

Hi  BSAs4ever,
Welcome to the forum,
I'm sure the answer will be found here somewhere!!!
Firstly are you sure its the carb setup is the problem??
Swap over the pickups and plug leads complete and see if the problem moves to the other cylinder.
Is the right hand plug wetting??
Are the points gaps the same on both cylinders?
Is the compression good on both cyls? check tappet clearances?

If its fuel starvation set up a trigger spray with some petrol in it and squirt some down the RH inlet when the motor is running and see if the RH pot chimes in!!!!
If this works you need to strip the carb again and check for blockage particularly on the pilot jet circuit
There are two tiny holes one at the engine side of the throttle slide the other under the slide, these feed the pilot mix to the engine.

I had a hard to trace miss on an A10 recently it turned out to be a dud valve spring which was only barely closing the valve!!!
HTH
John O R

[a10gf]

Welcome to the forum, I'm sure you will find help and inspiration to start tracing down the source of any problem.
A few pictures of you bike \ carb setup ?

Agree with chaterlea25, use GPSE (the Golden Path of Search & Elimination )
e

[groily]

Welcome BSAs4ever,
Agree it would be a very good idea to do the ignition swap checks first to see whether there's anything amiss from the magneto onwards.
The single float + chopped rh Monobloc with bottom fuel feed to the jet block was quite common in those days, but can be a bit sensitive. I have such a set-up on one bike ( paired 376s). It doesn't tickover properly on the side stand (and I haven't been able to make it do so yet), but it starts and runs evenly on both sides and behaves OK on the road.
I've found mine are better with a large alloy extension on the float chamber of the left hand carb, which provides a larger reservoir. (Typical period mod, although i'm not sure who sells them these days.) My carbs are pretty much parallel with the ground, but widely splayed. A steep downward angle might make things worse, but can't imagine it's that steep on a RGS.
Mine are jetted needled and set up the same both sides.
If the fuel taps and feed lines are clean, and the link pipe between the 2 carbs doesn't have an upward bend in it which places its highest point higher than the fuel level in the lh carb (which would be bad news and I can't imagine it!) the set-up should deliver loads of juice to both.
Is there a good flow at the rh carb if you slacken off the banjo fitting on the bottom of the thing? And, as chaterlea says, does the rh plug get wet? And are you sure the fuel level in the lh carb is correct - ie up to the dimple next to the cast 'AMAL' - if there is a dimple - on the float chamber lid.
Agree it would be a shame to ditch the period carbs in favour of a single one, but have to say I have thought about a pair of concentrics from time to time . . . heresy!

[BSAs4ever]

Wow - the response to my question was pretty awesome - - I will try doing some of the suggested procedures, although it won't be until another week or two.  I a little backed up with some other projects.  For anyone interested in seeing the bike, please go to U-tube and see the AMA article from the 2009 BSA Vintage Days event.  Type in a search for "Jerry Bingham" and it should come up.

Once again, Thanks for all the help - It is greatly appreciated.

Cheers & hope to meet you all one day,
BSAs4ever

[muskrat]

G'day BSAs4ever, luv the name,
                                           one other thing is the balance of the two carbs. Remove any air filters or bell mouths. Now twist the grip and use your finger to feel if both slides disappear up the top at the same time. Use the cable adjusters to make even. Then check that they both lift off the idle screws together. Use the screws to adjust this.
 All of the other suggestions should be checked as well.
I have run twin carbs for years but used concentrics. I drilled the manifolds and fitted small hose fittings to use vacuum gauges to balance carbs.
Cheers

[beezalex]

I think your carbs need to be set up from the beginning:  First off, is the float level correct?  Second, are the slides and cables synced?  Third, what throttle range is this running problem occurring in (Idle, cutaway, needle, main)?  Have the carbs been sleeved?  Have you looked at the plugs?

I've set this combination up on a Norton Atlas with the same carb arrangement with freshly sleeved carbs and basically had to start from scratch.  Prepare to learn a lot about monoblocs.

Cheers.