What would cause old tractor to loose power when worked hard

I have a 51 farmall Super A, that my grandpa has
turned over to me. It has done this for years.
Just doing light garden work etc..it runs fine.
But if you work it hard plowing a lot for a good
time it will just loose power and idle down. If
you turn it off let it cool it will run back fine.
I"m probably going to redo at least the top end
this winter if not the block also. You think it
just gets real warm from working hard and loosing
compression?

I"m not super engine savvy so trying to just see
what some of you think it would bee.

Bad coils usually show up when they get hot. Is the tractor running hot? Old engines do lose power when hot,compression as you have indicated,but then you said it has done this from day one so I think I would rule out compression until I did a test on the cylinders.Vapour lock is possible.

Internal engine trouble, rings, valves, cylinders, bearings, is going to show up long before an hour. Don't go nuts spending money on those things in haste. Don't overlook the simple. Simple is fuel, type (regular/premium) and flow (obstructions in the tank or fuel lines or filters; air (be sure air cleaner is free of obstruction; spark (as mentioned, coil, then spark plugs).

My Cub done the same thing and it was a bad coil

Another simple suspect to check out is the gas tank vent working properly. If not it will slow the flow of fuel to the carb as a vacum is created inside the tank. Its easy to check by loosening the tank cap when it starts acting up.

When it loses power check the fire to your spark plugs asap before the engine cools. Hal

(quoted from post at 10:44:26 06/10/14) I have a 51 farmall Super A, that my grandpa has
turned over to me. It has done this for years.
Just doing light garden work etc..it runs fine.
But if you work it hard plowing a lot for a good
time it will just loose power and idle down. If
you turn it off let it cool it will run back fine.
I"m probably going to redo at least the top end
this winter if not the block also. You think it
just gets real warm from working hard and loosing
compression?

I"m not super engine savvy so trying to just see
what some of you think it would bee.

Click to expand...

It IS losing compression. The valve lash is too tight. When the engine gets good and warm, the valve stems actually grow in length, and then the valves will no fully close, causing a compression loss and rough running. If this is allowed to continue, the valves WILL become burnt and eroded away.

Not sure it has done it since day one, my grandpa probably bought it close to 20-30 years ago from another family member I'm 28 and he's had it as long as I remember. But it has done it for years. But only thing it is used for is a garden tractor just laying off rows, discing weeds etc...and seems like only if your run it a long time.

I have removed the gas cap before when it was doing it did not change as it almost similar like it could be about to run out of gas...it doesn't spudder just idles down...and if you increase throttle idle stays the same (put if you tried to drive when it idles down it will cut off)

I just thought of it but it also maybe more when the fuel is lower say less than 1/4 tank...When it happen yesterday i removed the gas lid to check fuel. I saw it had fuel (but low). When I got home today went and fired it right up and drove it down to the building.

(now this may just be coincidence cause it happens after you run it a while or might be a fuel issue?)

The time before it was lower fuel also actually really low that time. I refueld and that was with 93 and it wouldn't start back up after sitting couple hours I drained the gas and put 87 in next day and it fired up. I've also had to pull it off with another tractor before to get it to start up when it has done this.

Also no tractor isn't running hot. radiator and fan are cooling no coolant leaks etc...

Bet you have a bad coil.

Allan

It has been converted to 12v, the coil shouldn't be too hard to swap is it?

If you've been through all the easy stuff, plugs, points, fuel flow, etc, you can try a coil too, not a big money item. I'd pull the valve cover and check the adjustment on the valves, maybe do a comp. check cold/hot too.

(quoted from post at 18:38:05 06/10/14) It has been converted to 12v, the coil shouldn't be too hard to swap is it?

Click to expand...

No, it is not difficult. You just have to keep track of where the two small wires are connected, and connect the new coil up EXACTLY the same, unless it is connected wrong now.

Before you go swapping coils: Is there a ballast resistor in the wire from the ignition switch to the coil? It is a white ceramic block about the size of your thumb.

If there is no ballast resistor, you have found your problem. The coil is overheating because it is receiving 12V instead of the 6V it is designed for.

If there is no ballast resistor now, make sure you get a new coil that says, "No ballast resistor required."

I don't believe there is a ballast resistor, but it
might not be the original 6v coil. I'll see if i
can get some numbers off the coil and a picture or
two.

I'll see if i can find picture or original 6v coil
to compare too.

One more is you must have wire core ignition wires! Check to see if you got one of the "Modern" caps. They made them for awhile with aluminum instead of copper contacts in the cap.