rpm changes while driving on m38a1

[Gillinski]

Hi everybody!

I have an m38a1 whith carb, ignition and timing adjusted, worn parts replaced. The carb is rebuilt with a midwest kit.

I have one problem: I have to adjust the rpms with throttle cable while driving!! I give you an example:

1) Starting fine immediately (when cold --> choke pull out for 5 sec.) with correct idle.
2) Then driving fine and runs great, but i feel that when i push the clutch to change gear, the rpms falls down very low.
3) At the next stop the rpms are so low that the engine dies sometimes. Then i start engine again and pull out throttle a bit. rpms seems ok
4) At the next stop the rpms at idle are much bit too high, so i push the throttle in a bit until rpms are ok
5) At the next stop, idle rpms too low, engine almost dies, pull throttle out and so on....

Sometimes i adjust the idle speed screw on carb, but it's the same thing: It variates between too high and too low

Any idea?

Gillinski

[wesk]

Did you replace the throttle plate shaft bushings? A varying air leak around the ends of the throttle plate shaft will give you this problem. If you have more than .002 play in the shaft vs it's hole you need to fix it.

[Gillinski]

Your response sounds logic to me, but that bushings were in the kit which i used to rebuild the carb. Could there be a problem with the shaft or the plate? Perhaps the shaft is worn???

Thanks
Gillinski

[wesk]

The shaft wears more in an oval shape. So when you check for excess play be sure to slowly rotate it thru it's full travel.

[zikyzalzman]

you have an air leak, to know wher it cam just use the spry carburetor cleaner or wd-40 and spry it on the inlet manifold or the base of the carb
and listen to the rpm engine
pb you dont have a boster brake????
good luck
zikym151a2+m37