Starting Issues

[Good Hope Farm]

We have a 1977 IH Cub tractor in Cary, NC currently experiencing starting issues.
Background: tractor was maintained and running fine for year, then, over the last six months, began to show some irregularity in the engine operation. Initially, when the key was turned, it would start up and then rev very high, then finally slow back down to a regular idle after a few minutes. After a couple months, when the key was turned, the engine would start, but would rev very low and as soon as the hydraulics were engaged even slightly or it was put into gear and clutch released, it would shut off. Finally, it would start, rev low, then shut off. Actions taken: check and refill fuel, clean fuel bowl, replace fuel bowl screen and gasket, confirmed fuel is reaching carb, replace spark plugs and confirm spark at each cylinder, check oil and refill, thoroughly disassembled and cleaned carburetor, inspected linkages between governor and throttle controls, confirmed battery is good. Currently, it will not start but does turn over strong. It seems like it wants to start and after multiple attempts, fuel comes out of the carburetor as expected. With fuel, air, and spark confirmed, what else might I take a look at to get it running again? Compression loss due to gasket or governor are two issues I'm thinking, but seeking advice on anything else to do before that. Thanks in advance for any expert advice!

[Mht]

If you are certain it’s getting fuel and you have a good strong blue or white, not yellow spark at the plugs I would suspect compression issues. Cubs are notorious for valves sticking. I would pull the valve cover off the side and see if all the valves are moving properly. If not then address that issue. If they seem to be moving properly I would then check compression with a gauge. You could check compression first but that is hard to do with the hood on unless you have a right angle adapter for compression gauge. The valve cover can be removed with the carb on but it’s easier to get at with carb removed.

[Good Hope Farm]

Thank you Mht!

[Eugene]

Compession tests first, then ignition timing.

[Glen]

Hi,
Use a test voltmeter and see if the coil is getting battery power when the ignition switch is turned to the On, and Start positions.
People on here have had problems with the original IH key start ignition switches, they get so power doesn't go through them to the coil.
It might work in one position and not in the other position.

If you find power not going through the switch, you could remove the connector from the rear of the switch and clean the posts, and inside the connector.
Use fine sandpaper on the switch posts, wipe off all sanding with a clean rag.

A tiny screwdriver might work for inside the plug, and scrape it until it's shiny metal.

You might be able to get to the switch from the left side of the Cub.

If it won't work, TM Tractor has a new ignition switch, then you can use the same connector.
Below is the listing.

http://www.tmtractor.com/new/el/907fp.htm

[Good Hope Farm]

I completed the compression test and all cylinders showed around 100psi. I double checked the spark as Mht suggested and it seemed to be a weak, yellow spark. After replacing the ignition coil, the spark is still pretty weak. The spark plug wires and wire to the ignition coil have some cracking around the boot only, the wire itself and the internal metal connection seem fine. Could this wear be enough to cause a weak spark?

If unlikely, then would the culprit be the distributor causing the weak spark? As long as I have had it, the distributor has not been touched. If so, any tips on servicing the distributor while avoiding messing up the timing would be super helpful and appreciated. Thanks!

[staninlowerAL]

....any tips on servicing the distributor while avoiding messing up the timing would be super helpful and appreciated. Thanks!

Download a copy of the GSS 1012 Service Manual. You will have the correct maintenance and service instructions at your fingertips. Stan

[Glen]

Hi,
The 100 lbs of compression is good, but it could be more.
The Cub service manual says a 1977 Cub engine should have 120 lbs of compression, that is probably for a new engine.
I would charge the battery fully before doing the compression test.
Use the starter for the test.
The throttle should be fully open so the engine gets air for the test.
All the spark plugs should be out of the engine at the same time.

If the throttle was at slow idle, it could make the test readings lower.

A good tune up is good to do to a Cub, if it has not been tuned up since you have owned it.

The Ignition points, condenser, distributor cap, rotor, spark plugs, and maybe spark plug wires, may need replacing if they are old, or damaged.

Dirty spark plugs can make it start hard, or not run good.
The gaps need to be set right also.
The spark plug gap is .025", the operator's manual for the mid 1975 and newer Cubs shows.

Cubs have ignition points, similar to what cars had in the past. The points get old and burned from use, then the engine doesn't run good.
The ignition timing is important, it has to be set right, or the engine can have less power than it should, or it might not start as easily as it should.
I would check the timing as one of the 1st things, if the engine has low power, or starts hard.
The Cub service manual says use a timing light, like cars used in the past.

Below are pages showing a Battery Ignition unit, and the points, and setting the point gap.
The Battery Ignition unit in the pics has the older style of coil IH used.
They later changed to the newer style of coil with the posts all at the same end of the coil.

http://farmallcub.com/rudi_cub/www.clea ... age-11.jpg

http://farmallcub.com/rudi_cub/www.clea ... age-12.jpg

TM Tractor, at the bottom of the page, has new points and condenser. NAPA has them too, the last time I checked.

I change the points with the Battery Ignition unit on the engine, then you don't lose the timing.

To change them, you need a short screwdriver, with a sort of wide blade, and an 11/32 open end wrench, for the nut holding the end of the point spring.
I sit down next to the engine, on a lawn chair, and use a good light. You can put a large towel on the ground, to catch any screws that might drop.
Or you can file the points flat, if they aren't burned much. Wipe off all filings with a clean cloth.
The point gap is .020", the Cub operator's manual says, for a Battery Ignition unit.
You need a flat feeler gauge to set the point gap.

Below is a page from the Cub service manual, showing the timing marks for the Cub engine. They are at the left front of the engine.
Use a timing light to check the timing.
Mark number 1 should be aligned with the pointer, when the engine is running at slow idle speed, about 500 RPM.
Use only the pic and the description below it, they are talking about other things on the page.

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

Check the timing with the timing light after setting the timing, and see if the timing advances as you speed up the engine. If the timing advance in the distributor is stuck, it could make the engine have less power than it should.
That is only on the Battery Ignition unit.

Here is info about checking the power of the spark, if you need it.
You could do a spark test and see if the spark is good, or not enough.
Remove the center spark plug wire from the distributor cap, hold it by the insulation with the metal end about 1/4" from a bare place on the engine.
Put the transmission in neutral, turn the ignition switch to on, and run the starter. The spark should be blue or white, and jump the gap. A yellow spark is weak, and needs improving, the engine may not run.
I would charge the battery fully before doing the spark test.
Be sure the Cub doesn't roll when sitting in neutral.

You could try an oil additive, and see if it helps the compression.
They say on here to put Seafoam oil additive in the engine oil.
They sell it at auto parts stores.
Several people on here that used it said that it helped a lot.
They say on here to make the engine work while using the additive.
If the piston rings are stuck, it can help free them.
It is common for piston rings to become stuck.
Combustion isn't perfect, and can leave goop on the pistons and rings over time.
That can make the rings become stuck.
They have to move freely in the grooves they are in to seal well.

One of the experts on here said to use the additive for 2 oil change periods.
The operator's manual for Cubs serial number 248125 and above says to change the oil every 100 hours of use.
If the rings are worn, the seafoam won't help much.