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M bogging down with or without load

H

hightraverse

New User
sorry if this has been asked before.... my M will run at high rpm for several seconds and then sputter and bog down temporarily whether at a standstill or under load. it recovers everytime. my thought is that the carb float may be getting stuck. putting in a new needle / seat this weekend. i don't think it's governor related since it gets to high rpm no problemo. it's a 1946 with split front wheels and 12 V conv kit if that matters. any other troubleshooting sugggestions?
 
so is the 12v system correct with a 12v coil and have you changed the condenser does the dist shaft have play
can you move the shaft back and forth
 
the 12V system was done by previous owner. it has a 6V coil with resistor. i will check the other things this weekend. it's 100 miles away. thanks for your response
 
Sounds like starvation at the fuel tank to me.

The letting it sit for 30 seconds lets the carburetor bowl fill back up.
 
it's pretty dingy looking. will do that this weekend also. isn't there also an in line filter where the gas line connects to the carb? sorry for the stupid q but i'm a newbie to this stuff.....
 
Pull the carb drain plug and make sure you have a good steady flow of gas that will fill a pint jar in less then 3 minutes. And yes catch the gas so as to look for water dirt etc.
 
(quoted from post at 10:26:24 07/11/18) it's pretty dingy looking. will do that this weekend also. isn't there also an in line filter where the gas line connects to the carb? sorry for the stupid q but i'm a newbie to this stuff.....
Click to expand...

Yes. There is a filter in the carburetor where the fuel line connects. It is a very fine mesh brass filter. It usually can be cleaned.
 
If there is a plastic fuel filter in the line, that could be the wrong kind of filter, meant for a pressurized system, that can't flow enough fuel. Or it could just plain be plugged.

FYI, don't worry if the inline fuel filter has an air bubble in it and isn't filling all the way. That means it's clean. When the filter is sitting full of fuel, it is dirty and needs to be replaced.
 
Another possibility is a sticky governor output linkage or carburetor throttle shaft.

Remove the cover from the governor riser ? the sloped cover with a vent tube coming out the top at the top of the governor. Under the cover will be the throttle shaft bellcrank.

Now with the throttle handle CLOSED (fully forward) the bellcrank should rotate through 90 degrees with no resistance whatsoever.
If the crank is stiff, loosen the throttle shaft tube clamps (2 screws at both ends). Wiggle the tube until it finds its natural ?center?, then retighten the screws

If it still does not move freely, remove the pivot pin from the bellcrank then check whether binding is in the carburetor or the linkage to the governor, then proceed from there.
 
Quoting Barnyard.. ....FYI, don't worry if the inline fuel filter has an air bubble in it and isn't filling
all the way. That means it's clean. When the filter is sitting full of fuel, it is dirty and needs to be
replaced.... Whaaat?? Anybody else use this ideology to diagnose a fuel system? I always
thought it was air trapped there. When it is gone it has just found a way to disperse into the fuel
stream. Not saying that an in-line fuel filter in a gravity system cannot cause trouble. Just not sure
that thought process has any value in your situation.
 
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