Ford 901 Powermaster

retired farmer

Well-known Member
Not my tractor, got conned into rebuilding the carburetor. Marvel Schebler TSX 769. It was missing the power jet in the bottom bowl but the guy said it ran alright. Didn't put one back in it. Got carb back on tractor today. Got it started and adjusted the air screw to two and a half turns out. Directions say to turn the power screw out until engine loses power. I can back the screw all the way out and the engine will die. Turn it all the way in and engine dies. Doesn't seem to have any effect on engine power. Even tried adjusting it while he was driving it up a hill. Have it set about halfway out now. Now it doesn't want to start unless you crank on it and choke it some. Runs fine after that. Any ideas on whether it needs the power jet in the bowl and why it is hard to start now? Where should power screw be set? He put an alternator and electronic ignition on it. Going to check the timing tomorrow. Also posted in Ford forum.
 
Some of those used a power valve, some didn't. If it ran without it, it probably never had it.

When adjusting the carb, be sure the engine is up to temperature and is properly tuned. If it has other problems, it will be near impossible to get a good carb adjustment.

Start with the idle stop screw, get it idling around 400-500 RPM.

Next adjust the idle mixture screw, the smaller screw just under the mount flange. This screw adjusts the idle air mix, so turning it IN enriches the mix, turning OUT leans it. Turn the screw OUT until the idle stumbles, then turn it slowly in to best idle, then about 1/8 to 1/4 turn further in. That will slightly enrichen it for easy no-choke hot starts.

Then adjust the main power jet. Start with the screw about 1 1/2 to 2 turns off the seat. Set the engine to full governed speed. Manually pull the throttle linkage to idle, and then let go of the link. The governor should quickly full throttle the engine until it gets back up to speed. (If this doesn't happen, revisit the governor linkage adjustments.) As the engine comes up to speed, listen to and watch the exhaust. The engine should take throttle without hesitating. Start turning the main jet screw in about 1/8 turn at a time, repeating the test. It will get so lean that the engine will stumble or die when accelerating. Start backing the screw out until it will take throttle without stumbling. A single puff of black smoke is what you want to see.
 
Thanks, I will try that. I was kind of doing that but it didn't act right. I have rebuilt Marvel carbs before and never had any problems with them.
 

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