Topic: Carbs "spitting"

[Harry]

When starting up cold, choke pulled, my carbs make an intermittant spitting noise which dissapears when the engine is warm enough to idle with the chole closed again. Who can tell me what phenomenon causes this spitting?

Thanks in advance.

Harry

[oldbiker]

Harry, as you know these fours run with an 'idle' spark which occurs when the piston is reaching tdc. on the exhaust stroke. At this point both inlet and exhaust valves are slightly open (called the overlap). If on the previous firing stroke all the gas was not burnt since the motor is cold and the choke is pulled any small remaining spot of gas could ignite and blow through the valves and carbs. This is all theory but it's a possibility.

[bryanj]

Usual reason is slightly tight inlet valve clearance.

[Harry]

Thanks, guys!