Engine Revs

[SV_Minor]

I have a strange issue that is flummoxing me. My 1932 Minor SV has a low idle speed when the engine is cold, which can result in the engine stalling, but when hot the revs are too high. I've had to get the screwdriver on the idle screw to reduce the revs. That makes the cold idle worse when I next use the car, but when the engine warms up again, the idle is high... even though I haven't adjusted the idle screw from the previous run when I'd lowered the idle speed. I've now run out of thread on that screw and the revs are high when engine is at operating temperature. What the heck is going on?!?!

[Ian Grace]

Jonathan,

Is the butterfly completely closing when cold and hot and with the slow running screw backed right off?

Is the piston bottoming at idle when cold and hot? if not, is the needle not perfectly centred in the jet?

No suction leaks anywhere?

Just some idle thoughts.

Ian

[SV_Minor]

I've taken the top off the carburettor and given the inside a clean. The piston is free in movement, and drops with a good clunk onto the base. The one thing I've discovered is an air leak past the butterfly flap spindle and carburettor body. That's got to have an unwanted effect on the fuel mixture.

[Ian Grace]

I hope that doesn't mean that the carb. body is worn out. Can it be bushed?

[SV_Minor]

Can't say at the moment. There wasn't any noticeable play between the spindle and the body, so I might be lucky.

[SV_Minor]

I do have a brand new spindle and a few other parts from a Burlen kit I bought when I part-rebuilt the carburettor back in 2017. I just decided not to go too deep on the rebuild at the time.