A puzzling problem

[staninlowerAL]

A repurposed lawnmower fuel tank makes a good pony tank.

[tst]

before blaming the carb make sure your points are gapped correctly and in good shape

[Don McCombs]

My version…

[DRaymond]

I had a similar head scratcher and after 25 hours of trouble shooting solved my mystery. After putting 11.4 hours of trouble-free running post restoration of my 48 Cub I drove "Marie" to the garage/shop entrance and shut down in preparation for adjusting the high RPM limit on the Governor (it was maxing out at 750-950 RPM). I restarted the engine which quickly slowed down and died after about 3 to 5 seconds. Tried many restarts after tinkering with the carb but the tractor continued to die after 3-5 seconds. The engine would just slow down its idle until it died each time. Fuel, fire, and air - If Ok it should run. It displayed all the symtoms of fuel starvation. I dipped the fuel tank and it showed about 6.5 gallons of 2 month old alcohol free gasoline. Fuel would come out of the Carb bowl when I removed the bowl plug and it was not leaking or flooding and the linkages to it were free. Fuel flow was about 0.3 gal/min at the carb. I had spark at the plugs, and the induction system was clean and clear. I Removed the carburator and checked the float level, and needle and seat action both of which were OK and in limits. I swapped out the Carb with a new one, and still the same problem. I filed and re-gapped the points and checked the timing of the mag and still the same problem. The Tractor restoration included the cleaning and installation of an IH carb kit as well as the cleaning, gapping, and replacement of the points, condensor and coil in the J-4 Magneto. THE FIX!!! I replaced the condensor and points in the magneto (only had 11.4 hours on them) with a new set and it cured the problem. Tractor fired right up, purred like a kitten and completed a 2-mile test run without a hick-up! I found out that a bad condensor can display these symptoms. Good luck.

[PFord]

I had a similar head scratcher and after 25 hours of trouble shooting solved my mystery. After putting 11.4 hours of trouble-free running post restoration of my 48 Cub I drove "Marie" to the garage/shop entrance and shut down in preparation for adjusting the high RPM limit on the Governor (it was maxing out at 750-950 RPM). I restarted the engine which quickly slowed down and died after about 3 to 5 seconds. Tried many restarts after tinkering with the carb but the tractor continued to die after 3-5 seconds. The engine would just slow down its idle until it died each time. Fuel, fire, and air - If Ok it should run. It displayed all the symtoms of fuel starvation. I dipped the fuel tank and it showed about 6.5 gallons of 2 month old alcohol free gasoline. Fuel would come out of the Carb bowl when I removed the bowl plug and it was not leaking or flooding and the linkages to it were free. Fuel flow was about 0.3 gal/min at the carb. I had spark at the plugs, and the induction system was clean and clear. I Removed the carburator and checked the float level, and needle and seat action both of which were OK and in limits. I swapped out the Carb with a new one, and still the same problem. I filed and re-gapped the points and checked the timing of the mag and still the same problem. The Tractor restoration included the cleaning and installation of an IH carb kit as well as the cleaning, gapping, and replacement of the points, condensor and coil in the J-4 Magneto. THE FIX!!! I replaced the condensor and points in the magneto (only had 11.4 hours on them) with a new set and it cured the problem. Tractor fired right up, purred like a kitten and completed a 2-mile test run without a hick-up! I found out that a bad condensor can display these symptoms. Good luck.

Welp, that was a long read but WELL worth it!

I've got some parts and tools on the way. I'll deal with those and then try things out. If I don't get a fix with them, I'll get a distributor rebuild kit. However, I'm thinking if your points were bad, a spark plug tester should show that up as very weak spark on one or more cylinders. I can run to the parts store and pick one of those up tomorrow and give it a shot.

[PFord]

A repurposed lawnmower fuel tank makes a good pony tank.

Thank you!

[PFord]

before blaming the carb make sure your points are gapped correctly and in good shape

Yep, I'll need to check them.

[PFord]

My version…

That's AMAZING!

[Don McCombs]

If I recall correctly, it was from a snowblower.

[Urbish]

I have a pony tank from a snowblower that is attached to a 2X4 with a hole in it so I can bolt it to one of the implement mount pads on the clutch housing.

[Gary Dotson]

Try some simple things first. Have you done a fuel flow test through the carb? Have you checked the carb. main jet for plugging? I suspect you have a Zenith carb. if so, the main jet is behind the brass plug, bottom rear of the carb. That plug is where you need to do your flow test at. If all is well there, move on to the points and condenser. Misadjusted points can very definitely cause different behavior on different cylinders and you would be amazed at all the weird thing a bad condenser can cause. New one fail more often than old ones. You may have an intake manifold gasket leaking but we seldom see that. It can’t hurt to pull it off for a look, though.

[PFord]

Try some simple things first. Have you done a fuel flow test through the carb? Have you checked the carb. main jet for plugging? I suspect you have a Zenith carb. if so, the main jet is behind the brass plug, bottom rear of the carb. That plug is where you need to do your flow test at. If all is well there, move on to the points and condenser. Misadjusted points can very definitely cause different behavior on different cylinders and you would be amazed at all the weird thing a bad condenser can cause. New one fail more often than old ones. You may have an intake manifold gasket leaking but we seldom see that. It can’t hurt to pull it off for a look, though.

I have not timed the fuel flow through the carb, though I know I am getting flow. I'll try to test it soon. I don't have a Zenith. And yes, I've pulled the main jet and cleaned it thoroughly.

I'll have to try to get into the distributor this week or weekend to have a look around. Wouldn't hurt to get a kit and replace everything n there. My gaskets have been ordered and are on the way. Now that I know I can get them easily and cheaply, that takes a load off my mind.

Thanks for sharing your thoughts.

[inairam]

did you adjust the adjust the valves. you have good compression but still the difference burn between the is something.

since people brought up points I have had problems with various ignition parts from the various tractor parts sites and have started using napa ignition parts.

again since there is a difference between the cylinders did you replace the spark plug wires?

[PFord]

did you adjust the adjust the valves. you have good compression but still the difference burn between the is something.

since people brought up points I have had problems with various ignition parts from the various tractor parts sites and have started using napa ignition parts.

again since there is a difference between the cylinders did you replace the spark plug wires?

I have not touched the valves, and I have not replaced the plug wires. My thought on the plug wires would I would expect ONE of them to go bad maybe. But the symptoms I'm seeing don't seem to follow plug wires. Cylinders 3 and 4 seem to be operating "as expected". Meaning I am running at nearly full choke and they are fouling. It's 1/2 that are the mystery. If the plug wires were bad (or even if there was an issue in the distributor) I wouldn't expect 1/2 to run lean on full choke.

[PFord]

While I wait for parts to come in, I changed the screen at the sediment bowl, and put on a new gasket. The screen was dirty, but not blocked. I'd say maybe 1/4 to 1/3 restricted. For grins I looked in each cylinder but didn't see anything I didn't expect to see. I also changed the oil filter since I had one and it's never easier to do than now. There was no gasket on the lid. Not sure why. I put a new one on there.

I'll pull the carb this weekend and see what I can see. I don't have a rebuild kit, so I may just split it and put it in the ultrasonic for a while, then reassemble. I do have the gasket set coming and it includes the one that goes between the two carb halves. Maybe I'll get lucky.