504 loses power after an hour

Tractor is 1960 504 Gas, C-153 engine, TA
Serial No. 4705 S-Y-CC-FF

Problem is this: Starts and runs great and after about an hour begins to lose power. If I'm running around in 4th gear, pretty soon I'm in 3rd and not long after I've got to limp along in 1st. At times it's almost like I'm dropping cylinders, like I'm firing on all four and then three, and if I idle it down in a lower gear it finds all four again, that's how it sound anyway.

Thing I've tried: I thought this was a moisture issue during the winter and it seemed solved by swapping out a clean dry distributor cap, but that wouldn't do it yesterday. I also switched the coil in case that was on it's way out. Thanks for any input.

Today it won't start at all, generally it had been running fine after an hour or two break. There's good fuel flow at the carb and the carb is clean. Now that it won't start at all it seems more electrical, but other than the coil I can't think of what would explain it. The points only have about 150 hours on them, but the plugs are pretty old.

Hugh: This has been a great tractor for me, I get every bit of the 45hp out of it, I've got a 5-shank chisel plow I pull with it and I can pull it 10 inches deep without a problem, just not today!

It won't run at all ? Good News!

To check for power at the points, hook up your voltmeter to the distributor body and the movable side of the points. Turn on the ignition and open the points. Be careful not to ground the moving part with your screwdriver. You should have 11 to 12 Volts.

If you have power there, move the lead from the points to either of the coil terminals. With the points still open you should have voltage there too. If so, check to see that the fuel shut off solenoid moves. There is a coil in there that could be heating up and going bad ( or has gone bad now). If that moves, shut off the ignition, and short the wire from the condensor to the distributor body. You should see a little spark. When you are sure that the little capacitor is discharged, set your meter to Ohms and measure between the wire and the condensor body. It should be infinite (open circuit). If not the condensor is bad. The ignition coil should measure between 3 and 6 ohms across the terminals (disconnect both wires first).

You should have bought a decent M if you needed more power than an H. Live power and hydraulics are overrated. Otherwise, bring it over and I will get it back to you in July.

Greg

Also follow the carburetor adjustment instructions carefully to get the idle right.

1 – Vapor lock. As the tractor heats up from working problem may be gas boiling in the tank and fuel line. (I have a gas Oliver 1600 and a 1650 - both sometimes have this problem when worked hard in hot weather.)

Solutions: Make sure the radiator front is clear to maximize air flow over the engine and gas tank. If the fuel line runs close to the exhaust manifold reroute it farther away, or wrap it in insulation. If your tractor removable hood side pieces around the gas tank take ‘em off. Finally if there’s missing heat shields over the exhaust manifold, or between the fuel tank and top of the engine, replace them!

(Note – you can frequently tell if vapor locking happening by looking in the gas tank filler. If you see the gas is “boiling” – even lightly – it’s too hot!)

2 – Overheating coil (wrong coil installed). If the coil becomes too hot to touch after running 10 – 15 minutes you’ve got a 6 volt coil being fed 12 volts. Either replace it with an internally ballasted coil, or add an ignition ballast resistor in series with the primary to the coil.

3 – Failing condenser (long shot). Could be the condenser goes away as it warms up. For the couple bucks a new condenser costs it won’t hurt to simply replace it.