Posted by Alan Bowes on September 16, 1997 at 13:50:06:
In Reply to: Flathead engine problem posted by Will Pace on September 08, 1997 at 21:37:03:
: I have a '53 M-42 with what I think is a carburator/fuel related problem.
: It will start and run great but only with a slight amount of choke pulled out.
: If i push choke it runs poorly. With choke cable in and I choke by hand at snorkle
: ( it has fording kit) it clears up and runs ok.
: If I rev the motor it will try to die when it returns to idle. If it does die it will not restart
: for about 20-30 min. I have sprayed wd-40 around gaskets to see if there is a leak but the idle speed did
: not change any when I did this.
Here are a few thoughts.
If I read your posting correctly, it idles better when choked a bit, probably indicating an overly lean idle condition.
This could be caused by a vacuum leak, but it would probably have to be a fairly significant one, rather than just a small crack in a vacuum tube or something like that.
My first suspicion is directed toward a problem with the idle circuit in the carburetor. There are several possible causes: debris, worn throttle plate shaft/bushing/carb body (not allowing the throttle plate to align properly with the idle orifices in the carb throat), broken or bent tip on the idle mixture needle screw, etc.
If you were having problems at a higher engine RPM, I'd suspect the power circuit in the carburetor. There is a step-up or 'power' piston that raises and lowers a graduated needle in the jet orifice. Any corrosion, crud, or a bad spring on this piston can cause it to malfunction, significantly affecting the mixture at above-idle speeds.
If it idled OK and it hesitated or killed when you opened the throttle, I'd suspect a problem with the accelerator pump.
If you do a good job rebuilding the carburetor, it should fix any of the above conditions.
Regards,
Alan