Intermittant starting problem

[Colin White]

I have an occasional starting problem when warm with my 1974 CR. Normally when starting warm I start with 1/4 to 1/3 throttle (obviously no choke) and it picks up immediately. On occasion if it doesn't pick up and I going for another start it'll pick up with more throttle and only run at 2500 - 3000 rpm and above and appears to be very rich (black exhaust). If I try to drop the revs it dies (as though there is no spark) This can happen 4 or 5 times and then either it'll start as normal or I have to leave it for 5 or 10 minutes and try again.

 

I have 2 theories as to what's happening:- (1) the PI system has flooded the engine and takes some time to clear, or (2) there may be a problem with the ballast resistor as there would be a spark (12v) during starting from the starter solenoid bypassing the ballast circuit, and when I release the starter the ballast circuit doesn't take over the spark.

 

I am planning to try a 12v coli and bypass wire to see if it's problem (2) but I was wondering if others have had a similar problem with the PI system flooding on occasion.

 

All suggestions welcome, thanks

 

Colin W

Adelaide, Australia

[Peter Cobbold]

Colin, Normally I'd suspect the spark before the PI. But, yes, the symptoms do sound like flooding. I'd spray some WD40 behind the plastic cover on the MU. The fuel cam-follower may be sticking and not allowing the diaphragm to pull it upwards. So fuelling no longer falls according to manifold suction when you close the throttle.

When the engine is off the cam follower sinks to the low, max fuel, position, maybe it sometimes sticks there when hot.

Peter

Edited November 12, 2014 by Peter Cobbold

[Colin White]

Thanks Peter, definitely a plausible theory which fits the symptoms. Will do as suggested and see how we go.