I will be corrected if I am wrong, BUT, I believe that if you lift the rear
piston and it wants to die, that means your FRONT carb is to rich. That should
the one you should adjust IMHO. That is how I do it at least. I raise the piston
on one carb and adjust the OTHER carb till raising the piston on the original
carb causes little change in idle.
Bill Gilroy wrote:
> I am still having problems adjusting my carburetors. My car is a 77
> Midget with a 1500cc spitfire engine. I have replaced the original ZS
> carburetor with twin SU4, ala UK specification.
> The front carburetor seems to be adjusted about right. I lift the
> piston with the lifting pin and the idle speeds up briefly and then
> returns to close to normal. This carburetor is adjusted about 14-15
> flats out.
> The back carburetor is the problem. I lift the lifting pin and the
> engine wants to die. That is with the carburetor adjusted 12 flats
> out. I have borrowed a CO tester in an effort to better understand
> what is the problem. With the carburetor at 12 flats out, the CO meter
> reads about 2%. I continue to back the jet out and get to about 18-20
> flats. The CO meter goes to 8.5% and when I lift the lifting pin the
> engine still wants to die. The engine speed never increase and if I
> leave the pin up the engine will die. Any idea what is going on with
> my engine. The CO reading says the carburetor is running rich, the
> lifting pin says it is running lean. Something is wrong but I am
> stumped. Both carburetors are new and in good shape and I believe the
> reading on the CO meter. Any ideas or pointers?