Engine surging badly

[cub67]

Hi all, I just picked up my second cub a few days ago. A non running 55. After cleaning and setting the points, cleaning out the gas tank and carb and priming the oil pump she fired up for the first time in at least 5 years as I was told. Then after repairing a bad shift fork the cub was mobile! I spent the next day changing fluids and adjusting things. The engine runs really good and smooth and accelerated pretty good too. I made the governor to throttle linkage adjustment and noticed that the rock shaft extension had a lot of play in it so I took if off and shimmed it up. Made the adjustment per manual. Now it surges like crazy. I have tried to adjust the bumper screw, re set the linkage adjustment 3 times and read probably every thread here that contained engine surging. I am stumped. I drove it around yesterday for over an hour proud as could be but today I couldn't get it out of my building. If I grab the linkage the surging will stop until the rpm is increased then it starts again. If anyone has any idea what I could try I would appreciate it. I was going to pull the governor housing off tomorrow and see if something in there might be causing the problem???

[TallCoolOne58]

I think pulling the governor housing might be a good plan, with an eye out for a bent or broken bumper spring.

Another thought, how's the governor spring?

[tmays]

I would suspect fuel flow problem first. Yeah I realize you may have cleaned it all, but I’d recheck before I pulled the governor.

[Eugene]

I would suspect fuel flow problem first. Yeah I realize you may have cleaned it all, but I’d recheck before I pulled the governor.

Agree. Check the fuel flow and clean the carburetor main jet.

Then double and triple check the ignition timing with a timing light.

Also adjust the valve tappet clearance and conduct compression tests.

Basically, I'm suggesting to make sure everything is in good order before you start tearing into things.

[Waif]

I leave a piece of wire on each Cub to check the main jet.
Of course that has reduced/eliminated needing to use one often. So far....
But it's an easy check.

Carb could be choking/restricted from crud in a line ,or at the inlet screen if it has one.
Make sure your fuel tanks vent is working too.

[inairam]

It is almost never the governor itself. Check the fuel flow and jet as others suggested and adjust the linkage between the governor and the carb. Make sure the tips to the rods for the choke and the governor linkage connections to the carb are clean and lightly lubed so they do not bind.

[Dale Finch]

In your initial post you said you "shimmed up" the rockshaft extension because it had a lot of play. Are you sure it doesn't still have a problem there? Was the play located where the shaft enters the governor? If yes, there is a small woodruff key that can wear, and a quick fix many have done is to pull that shaft out, clean it up and reinstall it with a dab of JB WELD.
Just a thought.

[cub67]

Wow a lot of good things to look at here. Thank you everyone. I will pull the main jet and clean it again. On the governor shaft extension what I did was pull it out and wrapped a pc of an old pop can around it in a "c" shape to the woodruff key to get rid of the radial play. JB weld is probably a better idea. I pulled the bumper spring out. How long should the spring be sticking out of the bolt? Mine is maybe 1/4 to 5/16" of spring exposed. I'll report back in a while!

[inairam]

Also check for an air leak on the carb to manifold seal. Picture of a new spring http://www.tmtractor.com/new/gv/1006fp.htm but that is not causing the surging.

[yellercub]

I had that problem and here is what seemed to be the problem. The top of the carb. was warped, so after flatting it and setting the float and an adjustment to the linkage yoke (the yoke that links to the gov. arm) the problem went away for me. Hope this helps. Good luck.

[Flemmingth]

If you take the governor apart, look out for this viewtopic.php?f=1&t=101027#p798500

[Waif]

IF carb was removed to clean ..Checking choke lever position at carb is a quick check too.

[cub67]

Hey all, thank you for all of the responses. I was able to get it settled down by cleaning the main jet (again) and re adjusting the control rod properly. The cub is running pretty good and the governor is responsive to load so I think it is ok. That carb top is warped pretty bad as it is always wet but I can live with that for now. I'll read up on possible solutions for that!

[Don McCombs]

You should have been at The Tug this weekend. You could have gotten that warped top fixed.