power loss when hot

Any ideas, generally, what would cause a four cylinder gas engine to begin to lose power when it gets really warmed up? It acts as if its running out of fuel. It will run fine if you idle it down and only does this when its been pulling very hard and has really heated up.

What tractor? Gas or diesel. Has it just been rebuilt? Pistons too tight? Wrong gas?

First check fuel flow , next make sure that the fuel screw is atleast 4and a half turns off the seat . Next up the grade of gas to a higher octane. Makes a world of difference.

what engine? was it just o/h ? if the pistons dont have clearance it can do that.could be fuel also, hard to tell from the info.

Actually, the tractor is a Ford 4000.. but I"ve always gotten better info on this site.. its not a recently rebuilt engine and performs well enough the rest of the time. It is a gas tractor. I was hoping there might be some "typical or universal problem" that could be identified... I suspect its fuel related, but not really sure how.. fuel tank is directly over the engine and its likley its heating up the fule, but still not sure how that could cause the symptoms. (and, by the way, its a buddy's tractor and he asked me.. so I'm relaying the question for additional help.)

(quoted from post at 23:44:05 08/23/11) Actually, the tractor is a Ford 4000.. but I"ve always gotten better info on this site.. its not a recently rebuilt engine and performs well enough the rest of the time. It is a gas tractor. I was hoping there might be some "typical or universal problem" that could be identified... I suspect its fuel related, but not really sure how.. fuel tank is directly over the engine and its likley its heating up the fule, but still not sure how that could cause the symptoms. (and, by the way, its a buddy's tractor and he asked me.. so I'm relaying the question for additional help.)

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Probably dirt in the tank. It is getting enough fuel to idle and run along normally fine, but when you are pulling hard it uses the fuel faster that it is getting it to the carb. I had the same thing happen on my A Farmall this spring discing the garden, shortly into a hard pull it would spit and sputter and I would have to get off and clean the sediment bowl out and blow back up into the tank, it would run fine again for a while and then the piece of rust would find it's way back over the orifice. The problem with mine is that it usually doesn't have very much gas in it, because it doesn't get used that often and the inside of the tank is starting to get a rust problem. I'll probably seal it soon.

Check the fuel flow from the tank to the carburetor and open that main jet adjusting screw
as this will enrich the fuel mixture. Most garden tractors and big mowers have that feature.
Hal

(quoted from post at 18:39:53 08/23/11) Any ideas, generally, what would cause a four cylinder gas engine to begin to lose power when it gets really warmed up? It acts as if its running out of fuel. It will run fine if you idle it down and only does this when its been pulling very hard and has really heated up.

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3 things I can think of will do that.

#1 Vacuum leak at the manifold gasket
#2 Ignition coil
#3 Valve gap clearance.

My first guess would be the coil's going bad. Check the spark before and during the problem.

Much less likely, but possible, would be a bad vent in the gas cap - but so easy to check that it's worth doing. Just remove it hen you're having the problem.

When the problem's happening - I'd play with the choke - half choke it, see if that makes a difference. If it does, you know you've probably got some fuel blockage problems in the carb. But that would be a coicedental problem since it doesn't really fit what you described. But again - a free, simple test.

I'd adjust the valves. a little less simple to do, but still free.

If the points/condensor's old, just swap them all out for the fun of it. But now you're spending money.

Gas percolation and boiling does happen. Putting a reverse flow fan that blows through the radiator can reduce cowl temps radically.
An electric fan on the radiator instead of the belt driven is very good, and saves HP.
Putting foil insulation blanket between the engine and tank can be very helpful. Insulating the fuel line with rubber tube split to fit over is also good.
A coil going bad can be affected by heat, and breakdown under hot load conditions.
Jim

(quoted from post at 18:39:53 08/23/11) Any ideas, generally, what would cause a four cylinder gas engine to begin to lose power when it gets really warmed up? It acts as if its running out of fuel. It will run fine if you idle it down and only does this when its been pulling very hard and has really heated up.

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My [u:98774906f4]first[/u:98774906f4] suspect would be a coil getting hot and failing.

A good way to rule out fuel being hot is to put a bunch of wooden clothes pins (the spring type) all along the fuel line and run it - if it improves, the you have fuel percolation (beginning of vapour lock), but, the Fords aren't really known to be bad about heating the fuel.