Cub Cutting Out under a Load

Fri Jun 20, 2014 8:20 am

Hey Guys!

My '47 Cub's been acting up for a while. It runs smooth as silk at low, medium, and even high idle speeds. But when I put it under a little load, like maybe engaging the mower deck while crawling a slight incline, it starts cutting out and will eventually die if I don't stop it and lower the throttle considerably. I've been looking at the engine troubleshooting page and trying to rule out a few of the possible causes. So far, I have:

Replaced the coil.
Cleaned the main jet in the carb.
Checked the air cleaner.
Inspected the distributor cap and contacts.

Nothing that I've done so far has helped. What say ye experts?

Re: Cub Cutting Out under a Load

Fri Jun 20, 2014 8:36 am

First thought, partial restriction in the fuel system, limiting the fuel flow. If it's a fuel flow problem the stumbling should show up perhaps 30 seconds after applying the load. Engine should have plenty of power for the 30 seconds or a bit more time until the fuel level drops in the carburetor.

Second thought, low compression. Suggest a complete engine tune up including compression tests. Complete tune up will correct a slight ignition timing problem.

Re: Cub Cutting Out under a Load

Fri Jun 20, 2014 9:34 am

jpate831 wrote:Hey Guys!

My '47 Cub's been acting up for a while. It runs smooth as silk at low, medium, and even high idle speeds. But when I put it under a little load, like maybe engaging the mower deck while crawling a slight incline, it starts cutting out and will eventually die if I don't stop it and lower the throttle considerably. I've been looking at the engine troubleshooting page and trying to rule out a few of the possible causes. So far, I have:

Replaced the coil.
Cleaned the main jet in the carb.
Checked the air cleaner.
Inspected the distributor cap and contacts.

Nothing that I've done so far has helped. What say ye experts?


I am by no means an expert, but the experts here gave me the guidance that I needed to fix my problem last year which was just as you described. My governor linkage was not properly adjusted and the governor was never able to compensate for the loads. Just like you, going up a slight incline my engine would die just as it did when I raised my front blade. Try this: with your Cub at 1/3 throttle, grab the linkage connect from the carb to the front of the tractor and give it a slight forward and backward push. You should feel some resistance as the governor tries to adjust against you. If not, that's probably your problem. Check the manual...the necessary adjustment process is pretty clear. Hope that helps!

Re: Cub Cutting Out under a Load

Sat Jun 28, 2014 10:17 pm

Well, it's fixed.

When I first restored the Cub, it had a flooding problem. It would flood, and gas would leak out of the breather side of the carb. But when it was running, it ran great, even under a load. Last year I "fixed" the flooding issue by adjusting the float. This immediately took care of the leaking, and I thought all was well. Unfortunately it died on me 3 or 4 times after that in the parade last year. At the time I assumed it was bad gas or something. But I didn't connect the two issues until yesterday. Every time it died in the parade, it was also under a little load going up a hill, pulling a trailer full of riders, etc.

Anyway, I readjusted the float today, and I think I found the sweet spot. It runs great under load now, and it doesn't flood or leak.

Once again, I have met the enemy, and he is ME!!

Thanks Guys.

Re: Cub Cutting Out under a Load

Sat Jun 27, 2015 10:32 pm

And now...the rest of the story.

I thought the readjusted float had solved the problem, but it hadn't. I was still experiencing issues. Even when idling at full throttle it would run great for a few minutes and then just die, like you turned the gas off.

As part of troubleshooting, I drained the carb. The gas ran out quickly, but once the bowl was empty, it just dripped. There was not stream at all. I took the carb off again today, thinking it might need a little more float work. When I took the carb off, I decided to test the flow from the tank to the end of the fuel line, just to make sure it was flowing freely. To my surprise, it was just a drip as well. I was expecting a full stream the size of the fuel line. Upon further investigation, I discovered that the old shutoff valve had almost stopped working completely. Opening it "wide-open" resulted in only a drip. I ran a wire through the line and inside the tank, but it made no difference. I put a new fuel strainer assembly on it this afternoon, and it's like a new tractor now. Plenty of power (for a Cub, anyway), and no sputtering and unexpected shutoffs. I'm sure draining the tank and putting in new gas didn't hurt anything either. I think she's ready for a good bath and then the tractor show! And I'm HAPPY, HAPPY, HAPPY!!! :D

Just thought I'd let you guys know how it turned out.

Thanks.

Re: Cub Cutting Out under a Load

Sun Jun 28, 2015 9:33 pm

Always nice to know it got fixed. :{_}: If you still have the old sediment bowl remove the valve assembly and look for crud in the valve seat area. The path of gas isn't straight through. It comes down the tube from the tank, then makes a 90 degree turn through the valve seat and then turns again to head on to the sediment bowl. These turns can collect crud or the seat itself could. Depending on the style you may have to screw the handle along with the packing nut to get the valve assembly completely out. Clean it out, put on a new gasket, and some packing if needed and set it on the shelf for a spare.

Re: Cub Cutting Out under a Load

Mon Jun 29, 2015 5:32 am

Don't try to straighten the brass handle to get the nut off, just unscrew the packing nut, then the handle from the body. Might have to work the two together to get it out. BTW, waxed dental floss makes a good packing material. Stan

Re: Cub Cutting Out under a Load

Mon Jun 29, 2015 7:28 am

My old one didn't have the brass handle. The new one does. The old one had a knob and really fine threads. It took probably 20 turns to open it all the way.