Cub not running correctly.

[Tractor Rod]

I am confused and not able to figure out why my cub will run perfect smooth at idle up to about 1/2 throttle then after that it runs rough and lacks like it is either starved for gas or choking out. I know this is going to sound crazy but let me share how this happened. This is a 1948 Farmall cub and I completely rebuilt the carburetor and put it on and it started right up and ran top notch. I decided to power wash this little jewel and after that I put in four new D 21 spark plugs. It started right up, but ran as noted above. It will run at idle, but as soon as you take it to full throttle it starts missing, but still runs. I thought it was starved for fuel, so I checked the fuel line and sure enough the sediment bowl was clogged up so I replaced it. I also put a new filter on it and when I tried to start it, it still is doing the same thing. Could I have damaged something when I power washed it or possibly shorted wires, ??????????? I can’t seem to figure this one out. Any help is much appreciated. Thank you.

[tst]

power wash, maybe water in distributor cap, points condition and gap, make sure carb main jet not plugged

[Bob McCarty]

If you used an inline filter it has to be rated for gravity feed. If it's designed for a fuel pump system the flow will be restricted. Did you reset the linkage from the carb throttle to the governor rockshaft after reinstalling the carb?

[Dale Finch]

In addition to the above, check that the plug wires are in good condition (easy to pull a wire loose when removing the wire from your plugs...BTDT!).

Also, double check that they are installed in the correct order (easy to get them on the wrong plugs...BTDT, too!!)

[Don McCombs]

Based upon your other thread, I assume that you have an IH carburetor on the Cub currently. There are two fuel screens in the Cub fuel system. One in the sediment bowl and one in the fuel intake of the carburetor. Check them both for debris.

[NJ Farmer]

Just a little tip for the future…..leave the POWER WASHER for the driveway or the lawn furniture. You don’t power wash tractors, cars or any other machinery that you care about. The reason why is the power washer injects water into places you NEVER want water to get into. It can pass through gaskets and seals and even force out grease from bearings. Just a friendly tip but of course it’s your toys and your operation I’m just passing along a bit of wisdom. Also for all you car buffs out there with clear coats…..power washing your car with a chip in the clear coat will destroy you entire paint job.

NJ Farmer

[Waif]

Did you try putting the old plugs back in?

Check your plug gaps.
Check your entire ignition system as mentioned now that you've violated it's potential health by possibly exposing it to high pressure spray. A thin film of crud can prevent , or at least reduce current flow. (A blown radiator hose for instance wetting a distributor cap underneath....)


The symptom of starving for fuel can be similar to not burning existing adequate fuel efficiently. Yes you had sediment. Doesn't mean no or too little fuel.
But while we're on fuel , make sure your tank is venting correctly.

As mentioned (again) be sure your filter is for a gravity feed system.

Multiple changes in a short amount of time makes it hard to determine from here which change wasn't of benefit when something changes performance...

By the manual , (and it was already asked if you adjusted linkage after replacing carb) ; you run the quadrant lever up and down while (in relation to) making adjustments. If it gets stuttering along it's range of travel you're not done adjusting yet.

[Glen]

I decided to power wash this little jewel and after that I put in four new D 21 spark plugs.

Hi,
A common things that happens to engines when pressure washing them is water gets inside the distributor cap. The engine doesn't run, or run right with water in the cap. Remove the cap and dry it and the rotor, with a paper towel, or compressed air. Use your safety goggles when using the air.
Dry anything else in it that looks wet.

You could have got 1 or more spark plugs that doesn't work right. Sometimes new plugs are defective, and won't fire, or they make the engine run rough. Try putting one of the old plugs in at a time, and running it, and see if it is better, if it ran right with the old plugs.

If you power wash, or just use a garden hose to wash a Cub engine, keep water away from the rear area of the fan hub. There isn't a seal on the shaft, and water can go in the hub, if it is the original style fan hub.
You might be able to see if it has water in it by checking the oil level, like the owner's manual says.
Remove the screw and turn the opening down, and see if anything comes out. If anything comes out, catch it in a clean can, so you can see what it is. The water can sit below the oil. If you have run it, and oil is mixed with water, the best thing to do would be remove the fan assembly from the engine, and hold it with the rear down, so the water and oil can run out.
Below is a page from the 1949 Cub owner's manual telling about oiling the fan hub. The hub uses light motor oil.
I use a pump oil can to put oil in the fan hub.
https://farmallcub.com/rudi_cub/www.cle ... age-28.jpg