Hard to start when hot

[Willc]

Hello guys. I'm a new member here. My family has a 1975 IH cub tractor that we have owned since the mid-late 70's. It's mainly only used a handful of times a year to mow two small pastures. Certainly doesn't get used enough... Recently my brother and I have been working to get it running strong again. We were experiencing loss of power and overheating. A year ago or so we installed the pertronix electronic ignition with new distributor cap, rotor and wires. It seemed to run better but not great. Still overheating and loss of power... In the last month we have changed spark plugs and adjusted the timing with a timing light - set it at 16 deg before TDC. It was previously way off (maybe 30-40 deg after TDC). I also did a quick break down and clean of the carburetor since it bogged down a bit at high rpm and would come back with a little choke. After all this the cub ran great for an hour or so running the belly mower with a pretty good load on the tractor. After that, I shut the tractor down for a few minutes and it wouldn't start for 20 minutes or so. I continued to cut grass until I experienced loss of power again. Engine would come back with a little choke. Think I have trash in the carb again...

My main question is why is it hard to start when hot? The coil was replaced by a tractor mechanic maybe 2-3 years ago. It gets super hot with key on and tractor not running. Coil temp seems ok (not too hot) when the tractor is running. This hard starting problem has been ongoing for a year or so now.

A couple of other things to note. The tractor mechanic cleaned and rebuilt the carb a couple of years ago. Also this past month, I ran a compression check and am seeing about 100 psi after several compression cycles on cylinders 1 and 2. Cylinders 3 and 4 jump up to 120 psi much quicker. Any input is greatly appreciated. Lots of great info on this forum. Thanks!

[Slim140]

Possibly a bad coil even though it's been replaced. Try another coil and see if that helps. When you say it overheats is coolant coming out of the overflow tube? If so that is normal, it will find it's sweet spot when warm, which is usually just below the top pipe in the radiator when cool then it rises when it gets warmer.

[Waif]

Shane has a good point with a coil being suspect.

Check your radiator fins for debris or an accumulation of dust.
Close up with a flashlight they may be dirtier than they look without one.

[Glen]

Hi,
Below is a page from the Cub service manual. With a Battery Ignition unit, the ignition timing should be set to mark number 1 in the pic, when the engine is running at slow idle speed, about 500 RPM.
The timing advances as you speed up the engine, so it is about at mark number 2 at 2000 RPM. That is when it should have the 16 degree advance, not at slow idle speed.
You didn't say at which speed you set the timing.
They are talking about other things on the page, the pic has the info about timing.

http://www.farmallcub.info/manuals/gss- ... 001-43.jpg

I use a garden hose with nozzle for cleaning the radiator fins, from behind the radiator. That washes the dirt forward. It comes in from the front, the fan pulls the air to the rear.
If there is lots of dirt in front of the radiator, you might need to remove the grille, and wash off in front of the radiator first.
If there is only some dust in the fins, compressed air works, from behind the radiator.
Wear your eye protection when using the water hose, or air.

[Willc]

Thanks for the replys! When we set the timing a few weeks ago, we set it at 16 deg. before TDC at almost full throttle. I will double check timing at idle and full throttle next time. I did clean the radiator fins some a few weeks back with compressed air. When I ran the tractor last mowing the pastures, overheating didn't occur but it was only 75 degrees out as opposed to the normally 90+ degrees outside. I'm hoping that issue is resolved. I'll bring another coil and test it out next time I'm out at the property. Will keep you guys posted but it might be a few weeks before I make it back out to work on the tractor. Thanks again.

[inairam]

If cleaning the radiator does not work at stopping the over heating to really clean the cooling system you have to take the lower coolant tube off and hit inside the block with a garden hose or power washer. rust tends to collect in the front of the engine block.