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Cub running poorly

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10-30-2012 02:26:17

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Recently had the throwout bearing replaced on my 1950 Farmall Cub with a 12v conversion, but since returning it is running very poorly. It starts, but acts like it is only running on a few cylinders and only seems to run smoothly close to idle until warmed up for 20 minutes or so. When advancing the throttle it will immediately stumble and then run and miss erratically. Any choke after running a few minutes seems to immediately kill the engine. The governor keeps trying to adjust the carb between the hits and misses.

So far I"ve replaced the distributor cap and rotor and all the plug wires. The plugs and points were changed last spring, and the fuel line replaced and a separate inline fuel filter eliminated at the same time. The carb was cleaned then as well and the gaskets replaced. It was running fine through the summer until the throwout bearing broke. Any thoughts?


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10-31-2012 13:24:38

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 Re: Cub running poorly in reply to beargap, 10-30-2012 02:26:17  
Sounds like this Cub has never run right. It shouldn't "stumble" ever.

Once you get the fuel and ignition tuned up, the tractor should sound like a sewing machine and rev like a hot rod, not sputter and pop like an old John Deere.

Did you run some fuel into a bucket out of the fuel line after disconnecting it from the carburetor? It should be running a full stream, not a trickle or dribble.

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10-30-2012 08:38:33

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 Re: Cub running poorly in reply to beargap, 10-30-2012 02:26:17  
Firing order correct??? Check it. Next when was the last time you serviced the air cleaner and dumped the water/dirt etc out of it??? Since choking it hurts that means it is running rich or the firing order is wrong. 1,3,4,2 is the correct order if I remember right. Reason I say to check the air cleaner is because since it is running to rich the air cleaner being clogged will cause that. Or it could be your running plugs that are to hot enough for this crap gas we have now days. Takes a hotter plug to keep them from fouling out

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10-30-2012 08:29:28

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 Re: Cub running poorly in reply to beargap, 10-30-2012 02:26:17  
A bit of a long shot, but when a Cub really gets jostled around it can sometimes loosen up some crud in the tank and restrict the fuel supply. If you're not getting good fuel flow at the carb, there may be a flake of something in the intake of the sediment bowl or stuff stuck to the screen. I suggest looking for that before taking the carb apart to clean it.

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gene bender

10-30-2012 06:39:03

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 Re: Cub running poorly in reply to beargap, 10-30-2012 02:26:17  
Remove the plugs lay them in order on the hood and comare. Now before putting them back do a compression check. Your plugs should all look the same and when they dont it tells you there are other problems.

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10-31-2012 13:15:37

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 Re: Cub running poorly in reply to gene bender, 10-30-2012 06:39:03  

Thanks for the several suggestions on how to fix the old Cub. Here's what I did:

1. Pulled and inspected the plugs - all had a grayish deposit around the electrode, but looked clean, dry, and free of oil

2. Verified firing order as 1,3,4,2 with 1 being at the 1:00 position looking at the distributor

3. Pulled the carb apart and inspected it. No dirt in the inlet screen and nothing observed inside. Cleaned with some spray carb cleaner to verify openings were clear.

4. Checked the air cleaner, which was a little low on oil but otherwise OK.

5. Started and observed that after warming up a bit it will run very smoothly, but only at idle. Advancing the throttle quickly immediately results in (brrp brrp) missing and poor running, almost killing the engine. Advancing slowly seems to allow it to speed up, but still seems to miss a bit periodically or a lot if under load.

6. Adjustments to the idle screw have little effect, so I left it about 1 1/2 turns unscrewed.

Could this be a problem with the governor? Is there an advance mechanism in that housing? This has a 12v conversion and I have never touched the timing or opened the governor in 20 years...just set point gaps by feeler gauge when doing a tune up. It almost always is used at just about full throttle and had been running well this summer, with an occasional stumble when pulling a load and turning uphill while the regulator catches up. I appreciate the advice as it is barely usable at the moment.

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Dude with a 300

10-30-2012 04:13:24

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 Re: Cub running poorly in reply to beargap, 10-30-2012 02:26:17  
Sounds like a bit of something might be in the carb. Try tapping gently on the side of the carb while the engine is running and see if it will dislodge it. I recently had the same problem and that solved it.


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10-30-2012 04:07:29

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 Re: Cub running poorly in reply to beargap, 10-30-2012 02:26:17  
I would first check firing order and firing on each cylinder and then I would pull the bottom plug on carb. to see if you are getting enough fuel.

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