Commando Mk III idling issue

I have been chasing an idle issue for months. The bike is a bone stock MKIII. It has about 14000 miles on it. Carbs have been reworked by Bruce Chessel. Points, condensers, plug wires, plugs have been changed and are new. Compression is 145 right and 140 left. Carbs balanced with tool. Ignition timing set via strobe. The right cylinder is lean at idle. It seems to run OK off throttle. I can see a decent amount of fuel trickling in the carb as it idles yet it is lean. I have checked the manifold for flatness, replaced the o-ring seal for carb to manifold, sprayed crap all over trying to find a vacuum leak but there appears to be no leak. I have removed the right carb and reverified the passages are clear. I swapped the float bowl ass'ys which had no effect. Running the mixture screw in (richer) helps but it still pops and farts, worse when cold. Hand choking right carb helps things.

Amal documentation says worn intake guides can be of issue. Before I pull the head, does anyone have any suggestions of things I may have overlooked. I have a lot of experience on this bike and engines in general but I am purplexed at this stage. Save me. I am tempted to roll the garage door down and breathe fumes.

Most likely that the pilot jet is blocked, a very common issue. Adjusting the mixture screw doesn't help so the only action is to gently probe the jet clear with a fine wire. There is more than one thread on this subject and if you go the main page on the site there is good information on the Amal Concentric, notably by Bushman who explaines the causes and cures.

Mick

Thanks much. Checking now. I wasn't aware of that site and the detail is outstanding. I have a nice wire probe with a wire of the proper size.I will clear the pilot with the tool.

I had the carbs cleaned and checked out by a professional who did a great job but it is possible the cleaning dislodged some crap that got in the pilot. I will let you know the outcome. It may be 14 hours or so. Kid is sleeping. There is hope. Thanks again.

0u812 said:

Thanks much. Checking now. I wasn't aware of that site and the detail is outstanding. I have a nice wire probe with a wire of the proper size.I will clear the pilot with the tool.

I had the carbs cleaned and checked out by a professional who did a great job but it is possible the cleaning dislodged some crap that got in the pilot. I will let you know the outcome. It may be 14 hours or so. Kid is sleeping. There is hope. Thanks again.

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A #78 drill bit is the correct size. Easier and safer would be to remove the mixture screw on the carb in question, then spray in carburetor cleaner, let it sit for a few minutes, then blow into the hole where the mixture screw was with compressed air. This is the first thing I'd try to fix an idle problem, because it's quick an you can't possibly wallow out your pilot jet. I've noticed that the residual carburetor cleaner makes the idle funny for a few minutes after I do this, so don't judge how good your idle is until you've run the bike for five minutes or so after doing this.

I have poked out my pilot jet with a #78 drill bit, but as a last resort. For a thorough cleaning, I'd prefer to remove the carb, soak it in a can of carburetor cleaner and then blow into the various openings into the pilot circuit with compressed air. The most effective way to blow out with compressed air is from the bottom, but you have to remove the float bowl first. If you plug the mixture screw and the air inlet screw with your fingers and blow from the bottom you'll clean out the 2 TINY holes at the edge of the slide. This is pretty much the only way to clean out these two holes, they are where the fuel/air mixture from the pilot circuit emerges to go into the engine.

-Eric

I had a similer problem on mine with new carbs, I fddled & farted about with the mixture screws, I was starting to suspect leaky valves & all kinds of things. In the end I followed the instructions on the bushman site to the letter -- problem gone.
It was badly adjusted/balanced throttle stops & cables & choke cables (one choke was protruding into the airway), only myself to blame , as my old maths teacher said, "more haste less speed". no amount of mixture adjustment would help until I got the balance right.
Terry

If you are not using electronic ignition, don't forget to check that the centrifugal advance mechanism is retarding the spark properly. If the springs are weak you may have trouble getting a steady slow idle. The retarding of the spark helps with the idling. The worst thing is if the spark is not at a steady amount of advance. I am not sure where the advance should begin exactly, but it should not begin to well above idle.