Single Amal Mk2 34mm Running Problems

I'll keep this short.

Try a stay up float. Not enough fuel  for one carb. as standard, 

Popping and banging is often (but not always !)  due to an intermittent ignition ,sometimes this is as simple as an oiled plug giving an occasional spark.

Hi Malcolm

It's very frustrating. 

Have you tried cleaning the Pilot Circuit?

Cold engine. Remove the pilot air screw, squirt in a small amount of carb cleaner. Wait a few minutes, wipe away any excess. Replace the pilot air screw.

Hope that helps

Air leaks?

Stan's the man...if the carburettor is clean and new and has the correct settings.. it isn't the carb. If it's a twin and one plug is bad, it will still run properly but badly on one cylinder.

Air leaks cause weird things.

The only other thing is stuff you can adjust.  You say plugs are sooty.  You are turning the pilot screws the right way?

Where is your Pilot Jet located? The Mk 2 has 2 locations, in the top of the float bowl and in the base of the carb. For all down-draught situations the pilot jet should always be in the carb base, Also make sure you have a 4 stroke main jet holder, the 2 stroke version is flat at the bottom whereas the 4 stroke has a boss at the bottom and sits further down in the well of fuel at the drain plug.

You may have bought a carb that before fitting would sit on a piece of glass or other confirmed flat surface at the manifold. Check it again for rocking.

It doesn't take a lot of over tightening  to cause distortion, not much at all in fact.

You need to halve the possibilities. I would try another carb , if no better then concentrate on the ignition system . Beg or borrow a carb

Small changes in plug gaps or timing  are unlikely to have much  effect on normal running ,however if your spark is tracking down a dirty plug insulator then a reduction in the gap may help reduce this. Once running  and working hard  the heat generated will sometime clear the plugs and  help starting ,however many plugs in production today have insulators that absorb carbon and are hard to recover. Most now  have a built in resistor which is ok as long as you dont double up with resistor leads or plug caps which can upset an already weak system. Plug grades that worked in the distant past may not be the best for light use in modern traffic conditions and with todays fuel brews.

The idling jet needle must be close to 1-1/2 turns out, otherwise the air velocity across the jet is incorrect and decent idling will not be achieved.

Change the jet size.

Check the cold start plunger has black seal fitted.