Running OK but........

Took the bowls off the carbs today after getting float needles, bowl gaskets, ect from Old Brits. Found the leak - there was NO gasket on the left bowl! Replaced both gaskets and needles with viton just the same. No leaks. Finnaly drove it - runs OK but has a stumble just off idle and when you rev it and release the throttle, pops back throught the exhuast. Pulls strong though. Idle mixture screws are about 3/4 to 1 turn out - seems to have the highest idle at that setting. Cold start likes full choke or you have a long afternoon ahead. Any suggestions for further checks? Thanks again

Sounds like the carbs are worn out............its possible to get Amal carb bodies sleeved, but unless you are wanting to retain original appearance, it might be a better idea to fit modern flat slide carbs?

That sounds like the problem I had early on in my Commando ownership. Starting from the air side, are you using the stock air box or a K&N? Further in, what size are your main jets? Since you mention the idle settings, it sounds like your idle jet is clear, but it's also a good idea to double check, it's tiny and clogs easily. Make sure you have the correct needle and needle jet. Make sure the balance pipe is not leaking, also the carbs to engine joint. If your carbs are old and worn they will pass too much air just off idle and make it hard to get the mixture right. I just decided to buy 2 new carbs to have a fresh place from which to start.

These are new 932 Amals that the bike came with. Don't know what needle and jet is in them. I am running the stock airbox with a K&N filter element, also new rubber boots from airbox to carbs ( originals were dry rot city ). I will check for air leaks on the intake runners as suggested.

ahh jeez...missing gasket means someone may have poked around in there before you, in the words of Hobot "kinda like a box of chocolates".
replacement 932's must have the inner ears milled or filed away to avoid interference with each other and subsequent air leaks at the manifolds, they may mechanically bump together otherwise. Check for this.
When the float needles were replaced the fuel level was corrected on both LH & RH, correct?
Since you will have the bowls off again, no doubt, make a written note of the main jet size number that is roll marked on the actual jet. Make a note about each, left and right.
If you pull the tops off take a look at the number of main needles id head grooves (at the cable end) and write that down too, left and right. Note also what setting groove the clip is in, for each again.
The slides have a wear groove at the top to indicate serviceabilty, go to the Amal web site they describe it there in the faq or tech section. My experience is that the slides can be rattling their brains out and it won't be the cause your particular symptoms.
Look at and make notes about the shape of the spray tubes. Make sure both are the same shape regarding cutout.
I'm being a bit amal here only because heresay has it that not everything is as it should be concerning new carbs from factory stock.
Twin carbs must be synchronized. Deviation from perfection will affect performance detrimentally.
Old Britts has a decent tech section covering this. There is no substitute for gauges for setting up the synchronizing unless you are experienced.
How are the throttle cables? is one sticking on return just a little more than the other?
Amal has some good reading on their site too.
Check out Jim Bushman regarding doing the sync setup, I think that's his correct surname spelling, as well.
All this is negating the other systems influence that may be contributing to the problem, i.e. compression, back pressure, spark timing, fuel quality as well as delivery and electrical connections.
Get yourself a box fan to keep the air moving while you make the idle adjustments.
I do like your comment about "pulls strong though" intoxicating isn't it?

Mixture screws should be circa 11/2 turns out. might run better if not pilot jet circuit is clogged if not blocked.

Hehe, life may be like reaching in e box of chocolates but life with a Commando is like living with a bunch of mixed nuts : )

myjota has my thoughts on your condition. Air screws should give fastest idle 1.5 turn out so your input implies a lean base line as does the symptoms, but can never ever forget the pilot jet tendency to crust up from zinc oxide decay. A nail can bump the valve seat on cold carbs to adjust float level, spray tubes are a slight press fit.

Also peek in throat and made sure the spray tubes are both mostly sticking up.

Oakland850 said:

Took the bowls off the carbs today after getting float needles, bowl gaskets, ect from Old Brits. Found the leak - there was NO gasket on the left bowl! Replaced both gaskets and needles with viton just the same. No leaks. Finnaly drove it - runs OK but has a stumble just off idle and when you rev it and release the throttle, pops back throught the exhuast. Pulls strong though. Idle mixture screws are about 3/4 to 1 turn out - seems to have the highest idle at that setting. Cold start likes full choke or you have a long afternoon ahead. Any suggestions for further checks? Thanks again

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Popping exhaust may be a rich, where popping out the back of the carb maybe be lean. Not a 100 percent sure on this but I may be close. Others will chime in. Airscrew adjustment is quite a process, sort of a rince and repeat situation. This is one of the most frustrating things and have pushed many to single carb setups.

If you are rich at idle, you need to turn the airscrew out a little more. Lean, in a little. Once you get a fair throttle responce with the wrist flick return to the idle screw. Once the best idle is gotten, return to airscrewThis process may ave to be cycled many time to achive the desired results.

No dought, due diligence is required to get averything just so with these Amals, new or used. If these are new 32's is there a screw in pilot jets? You should validate what you have making sure equality between carbs is presant. Mains, needle, needle jet, slide and pilot if you got them screwed in the bottom of the body of after removing the float bowl. The more you can relate, the less people will have to quess. What exactly do you got and it's application. You and we need to know.

Actually first thing is get ignition timing for fastest idle w/o back fire kick starts, then retard a tad to slightly slow the idle. Then move to carbs with float level the first thing to ballpark by measure then fine tune by air screw response to 1.5 ish.

If you don't have the new adjustable stay up floats, get them. No use trying to set the float level with a nail when you can do it with needle nose pliers.

Dave
69S