mach0415
Senior Member
Dad (TD) and I have restored the running gear and chassis of his 1929 Town Sedan. We have been able to run it around the yard, and the refreshed engine has about 1 hour of run time on it. The only thing that has not been assembled on the engine is an exhaust system.
The stock engine, water pump, dizzy, and Zenith 1 have all been rebuilt. Timing is spot on. The problem we are having is that it will only fast idle with 3/4 choke, but the choke has to be fully off to run at higher RPMs. It always has to be choked to start after its warmed up. Retarded or advanced timing doesnt seem to affect ability to part throttle, other than the fact that it is much smoother with full advance on a warm engine. A retarded idle will cause it to stall., even set on fast idle.
I took the lower half of the carb off to inspect float level and it seems to be fine. I reassembled it and readjusted the idle mixture screw to specs. There is no change, of course, but there is an audible change in idle quality when the idle mixture screw is set too rich or too lean, even with a set choke.
Also, the GAV seems to be working, as there is a change in choked idle closed vs. open. I did notice the carb actuator on the GAV is wet with fuel when the choke is moved from open to closed - not sure if that is anything indicative of the cause for my concern, though.
My hypothesis is that there is fuel starvation at idle that seems to transition to proper metering at part throttle, so there is a concern in the idle circuit, if that's possible on a Zenith. AND Is low run time and no exhaust backpressure a factor here?
Any suggestions/criticisms are greatly appreciated.
The stock engine, water pump, dizzy, and Zenith 1 have all been rebuilt. Timing is spot on. The problem we are having is that it will only fast idle with 3/4 choke, but the choke has to be fully off to run at higher RPMs. It always has to be choked to start after its warmed up. Retarded or advanced timing doesnt seem to affect ability to part throttle, other than the fact that it is much smoother with full advance on a warm engine. A retarded idle will cause it to stall., even set on fast idle.
I took the lower half of the carb off to inspect float level and it seems to be fine. I reassembled it and readjusted the idle mixture screw to specs. There is no change, of course, but there is an audible change in idle quality when the idle mixture screw is set too rich or too lean, even with a set choke.
Also, the GAV seems to be working, as there is a change in choked idle closed vs. open. I did notice the carb actuator on the GAV is wet with fuel when the choke is moved from open to closed - not sure if that is anything indicative of the cause for my concern, though.
My hypothesis is that there is fuel starvation at idle that seems to transition to proper metering at part throttle, so there is a concern in the idle circuit, if that's possible on a Zenith. AND Is low run time and no exhaust backpressure a factor here?
Any suggestions/criticisms are greatly appreciated.
