TR4/4A Still Learning: I'm Missing, But Only Slightly

[KVH]

I like the saying that "what's wrong with your SUs is your ignition." But I've got that cool new Pertronix on there and a new coil, to boot.

It only misses once, maybe twice, and only if I really jump on the gas. The miss is in each of 2nd and 3rd at between 2800 and 3500 RPMs. Sure doesn't seem very material, but it's bugging me.

I assume it's most likely fuel related? I'll check and clean the floats and needles. What about the mixture and dashpot oil? I'm opened at about 8 flats on each carb. The trick about raising the piston 1/32nd until the engine accelerates and then slows down, doesn't seem to work on my leading carb. It just seems to accelerate, and that was case even after closing all the way down to 4 flats and that makes no sense to me.

Any ideas or advice here?

 

[TomMull]

Sound like the front carb might be a bit ahead of the other. Make sure both carbs are going back to the stops at idle. You might have to loosen and tweak the throttle rod between the two carbs. If you do find the front ahead, then try lifting the pistons again. Too lean a mixture can cause the brief miss you describe.
Tom

 

[GTP1960]

I like the saying that "what's wrong with your SUs is your ignition." But I've got that cool new Pertronix on there and a new coil, to boot.

i'm experiencing a very similar problem with my 3A. I too, have a new dizzy w/ flamethrower III Petronix & a new 45v coil.
Will be very interested in how you resolve yours!

good luck!

Guy

 

[Brinkerhoff]

Yes, when you are unable to lean the mixture down with the nut it usually means fuel is leaking between the two small cork seals and the jet , allowing fuel to enter around the outside of the jet ,not the inside. Carefully examine the outside of the jet and remove any score marks with 600 grit and replace the seals. Extreme cases , replace the jet.

 

[PAUL161]

90% of fuel related problems are ignition related. Pertronix seems to be the cause of some of them. Wobbly shaft, loose or wrong tension advance springs can cause a miss at higher rpms. Put the points back in and see if the problem goes away, if it does, problem solved. PJ