961 gas engine running poorly when warm

lIONgEon

New User
My 961 (Ford Powermaster 901 series) acts up when it gets warmed up, such as when I'm pulling a plow or disc, or the weather gets above 70 degrees or so. It runs fine when cold, but then the engine sputters and dies (if I let it) as it gets warm. If I choke it when it's acting up, I can keep it running long enough to do a few more minutes of work or get it back to the barn. I let it cool down for a few hours or overnight, and then it does the same thing (runs fine for 5 to 30 minutes until it gets warm, then starts in with the sputtering and dying).

I believe this symptom started rather suddenly, last fall before I stopped using the tractor for the winter, rather than developing slowly over time. I don't have any history with the tractor yet, though - it's new to me, so it's hard to say for sure if this started suddenly or developed slowly.

I know it needs a tune-up, but this doesn't seem at all like the kind of problem that new points and plugs are going to fix. I'm not a mechanic or engine guy at all, but I do have a few tools and would like to learn how to diagnose and fix relatively minor, common problems in this and other old tractors. So, any hints, ideas what to look at, pointers, etc. are welcome.

Thanks,
-Larry
 
check your fuel line from the tank to carb. make sure its not getting to hot which will cause it to vapor lock. some of the old ford cars would do that. put tin foil around the lines stopped it. you also might try loosening your gas cap. may not be venting properly.
 
(quoted from post at 21:07:11 06/02/19) check your fuel line from the tank to carb. make sure its not getting to hot which will cause it to vapor lock. some of the old ford cars would do that. put tin foil around the lines stopped it. you also might try loosening your gas cap. may not be venting properly.
Just great pin ball you just had to use the words vapor lock. Not that I don't understand what you are saying. but hang on here comes the sh_t storm
 

I would start with checking for fuel flow restriction. You are getting enough gas for it to run well at low load but when you put a load on it and the governor opens the throttle you are not getting enough. There is a plug at the bottom of your carburetor float bowl. Turn the gas off at the tank, get a container that will hold a quart, hold it under the drain, open the shut-off and see how the gas flows. It should flow a steady stream and continue as a strong enough stream to half fill the quart in about a minute. When it slows to a drip you have verified your problem. After that remove the as line from the sediment bowl and try the test again. If the flow is now strong your problem is after that point. if it is still weak your problem is most likely the screen inside the tank. IGNORE PINBALL!!
 
It was/is apparently a problem with getting enough fuel through the carburetor, not a pseudo vapor lock problem or other problem. There was plenty of fuel flowing into the carburetor, but nearly none would drip out the bottom when I removed the plug.

I had made several changes, so I've changed more than one variable at a time. E.g., I had topped up the coolant, as I found it was about 3 quarts low due to a new coolant leak having developed, I routed the gas line slightly to keep it higher off the engine, cleaned out the sediment filter (but the screen on it was clear and shiny, possibly indicating the previous owner had changed it trying to cure a problem), and I rapped on the carb as well as turning the fuel intake adjustment screw back and forth a few times. So I don't know for sure what "fixed" it. I didn't get a chance check the fuel flow out the bottom of the carb after messing with it, as I had several hours of discing and other work to do (and have been able to do it with the tractor running reasonably well again), but it must be better than it was.

At this point, I'm hovering between "ain't broke, don't fix it yet" mode and getting ready for some preventive maintenance cleaning out of the carburetor.
 
(quoted from post at 23:19:38 06/07/19) It was/is apparently a problem with getting enough fuel through the carburetor, not a pseudo vapor lock problem or other problem. There was plenty of fuel flowing into the carburetor, but nearly none would drip out the bottom when I removed the plug.

I had made several changes, so I've changed more than one variable at a time. E.g., I had topped up the coolant, as I found it was about 3 quarts low due to a new coolant leak having developed, I routed the gas line slightly to keep it higher off the engine, cleaned out the sediment filter (but the screen on it was clear and shiny, possibly indicating the previous owner had changed it trying to cure a problem), and I rapped on the carb as well as turning the fuel intake adjustment screw back and forth a few times. So I don't know for sure what "fixed" it. I didn't get a chance check the fuel flow out the bottom of the carb after messing with it, as I had several hours of discing and other work to do (and have been able to do it with the tractor running reasonably well again), but it must be better than it was.

At this point, I'm hovering between "ain't broke, don't fix it yet" mode and getting ready for some preventive maintenance cleaning out of the carburetor.


What is the "fuel intake screw"?
 
It's a large screw on the top of the fuel intake side of the carburetor bowl, where the fuel enters from the sediment bowl
assembly. It's probably for adjusting a needle-type valve that would control the slow idle speed of the tractor. I don't have a
drawing of the carburetor, nor do I get to spend much time out at the farm where the tractor is looking at things, so sorry if
I've misnomered it.
 
(quoted from post at 06:44:56 06/08/19) It's a large screw on the top of the fuel intake side of the carburetor bowl, where the fuel enters from the sediment bowl
assembly. It's probably for adjusting a needle-type valve that would control the slow idle speed of the tractor. I don't have a
drawing of the carburetor, nor do I get to spend much time out at the farm where the tractor is looking at things, so sorry if
I've misnomered it.

What does it have for a carb? they pretty much all had Marvel Scheblers but some had or had put on Zeniths. Both brands have a large screw on the bottom for the main jet and a small screw on top which adjust the AIR for low speed mixture.
 

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