Forum

[Thumper Dave]

I have fitted a Amal concentric carb and I have been having a lot of problems getting the bike to run properly.
When starting from cold the engine sometimes spits back through the carb which would indicate an air leak. When I manage to get the engine hot it runs fine.
I took care when fitting the carb but may have some distortion of the flange/adaptor.
Is there anyone else who has had similar problems and are there any cures?

[Dennis C]

What bike? and carb size would help, is you have gone to a bigger than standard carb? this could be your problem.

[PeteF]

The fact that it runs fine when it's hot is telling. Are you using the choke when cold? If you are perhaps it doesn't need it?

[apparently lucky eddie]

If it is spitting back the mixture is too lean. Are you using the choke correctly if at all?

[Presto]

Why does a weak mixture spit back through the carb?

[Revband]

To explain it fully would take a lot of typing and this board doesn't allow much time. The simple explanation is that a weak mixture burns hotter than desirable and even after the exhaust stroke the air left in the cylinder can be hot enough to ignite the new mixture coming in.

[John R]

When using an Amal concentric, I have always used the choke just for experimentally adjusting the mixture.For cold starting, with the carb set up right, tickling on its own seems to do the trick.

[Bullet Whisperer]

Don't know if this will be of any help, but this is from a few days ago. Regards, Paul. ..... https://www.youtube.com/watch?v=IBOQEbonTK0