Surging at 3/4 throttle

Fri Oct 11, 2013 7:24 am

Hey guys, my cub has recently develpoed a surge at 3/4 throttle only. if I go from idle to 1/2 throttle it does not surge, and if I go from idle to full throttle it does not surge either, but if i go from idle to 3/4 throttle it will surge 3-6 times before it settles down to a constant speed. I have adjusted the governor at the locknut / half square at the front of the governor, but i cannot really notice any difference. I turned it in almost 1 full turn and it didnt seem to remedy the problem any.

Also, the problem does seem to get a little bit better once the engine completely warms up. Once warm it will only surge 2 or 3 times at most before it settles down. All linkages seem tight and I can see/fell no play in them. Im wondering if i am experiencing a lean condition at 3/4 throttle?

What do you guys think?

Scott

Re: Surging at 3/4 throttle

Fri Oct 11, 2013 9:13 am

Check to be sure the linkage isn't hanging up somewhere. How is the throttle rock shaft? If there's rotational slop in there it attempts at certain rpm's, depending on load, to settle on an engine speed but can't quite because of the excessive "roll" in the shaft. It would hunt more with no load on the engine and minimize or disappear under load.

Re: Surging at 3/4 throttle

Fri Oct 11, 2013 9:57 am

Thanks. Ill re-check the linkage tonight, but i am pretty sure there isnt slop anywhere. I spent quite a while last night wiggling every link to make sure. LOL.

The entire situation just seems odd to me. Ive run the cub every week this summer for mowing and it never had any sort of hunt, but yesterday, after sitting for a week, it started hunting. Im starting to think more and more that i have fuel problem because the governor seems to be re-acting correctly. There is no lag time for governor engagement. Just not sure why it is at only 1 throttle setting?

Re: Surging at 3/4 throttle

Fri Oct 11, 2013 12:12 pm

Most of the time issues like what you describe are solved by removing the brass nut on the side of the carb and cleaning the jet or
the linkage- binding or excessive play- but it sounds like you have that ruled out.

Almost NEVER is the governor itself the culprit.

Re: Surging at 3/4 throttle

Fri Oct 11, 2013 9:02 pm

As Bob said, it looks like you have ruled out the usual suspects. I suggest you go back to the bumper spring adjustment on the front of the governor. Remove it completely and you should find the spring. Check the spring for being gunked up, rusty, broken etc. Replace it if damaged. Otherwise, clean it up, oil it and reinstall it back to about where it was. If it still surges, give the adjustment another turn or so in.

Re: Surging at 3/4 throttle

Fri Oct 11, 2013 10:20 pm

I may have found the culprit. I decided to remove the bumper at the front of the governor and found that the spring is missing. Which is why the adjustment was not helping.

A couple questions:
Is the spring something I can find at a hardware store? Also, where would it have gone? What caused it to fall out?

Scott

Re: Surging at 3/4 throttle

Sat Oct 12, 2013 4:25 am

The spring needs to be a specific tension and length. Buy an IH spring. TM has them and they are a great sponsor and nice people to do business with http://www.tmtractor.com/new/gv/357fp.htm

Image

Re: Surging at 3/4 throttle

Sat Oct 12, 2013 7:25 am

Thanks. But I actually mean the small coil spring that is inside the governor. Inside the adjuster screw towards the front. Hopefully that makes sense?

Re: Surging at 3/4 throttle

Sat Oct 12, 2013 8:25 am

motoscott909 wrote:Thanks. But I actually mean the small coil spring that is inside the governor. Inside the adjuster screw towards the front. Hopefully that makes sense?

Scott, I had a similar problem and after taking the governor apart I discovered the bumper spring was missing. I assumed the previous owner had taken the governor apart and it either fell out by accident or he forgot to put it back in. It can easily fall out if you have the governor off the tractor, but it is impossible for it to simply fall out of a working governor (see below photo). In any event, I bought a replacement at the local IH dealer.
New Bumper Spring.jpg
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Re: Surging at 3/4 throttle

Sat Oct 12, 2013 7:21 pm

Part# 28 078 D $6.43 from Messicks.

Re: Surging at 3/4 throttle

Mon Oct 14, 2013 9:08 am

good news! I think i fixed the surging problem. :D I ended up removing the governor just to be sure there was no play in the linkage anywhere. It wasnt too bad, but there was some play in the "cross shaft" keyway (not sure if thats what its actually called) . I have read alot of guys use epoxy to fix this, but since i had no epoxy i decided to go another route. I removed the rockshaft and drilled and tapped a small hole opposite the keyway for a 10-32 set screw to fit in. When I tighten the setscrew on the shaft there is absolutely no movement.

As stated in my previous posts my "Bumper" spring was missing. I decided to experiment and got out my spring assortment. I found a spring that fit right into the end plug tightly and was about the right length.So I proceeded to Assemble everything, timed the governor and the mag, and set the linkage length. She fired right up and ran like a top. Absolutely no surging. It also seems to be much more responsive now. I can take off in 3rd gear at pretty low idle without stalling. The governor seems to react much quicker now.

The only issue I can now find is that from low idle I have to move the throttle 2-3 notches before the speed picks up. After that I have the full range of engine speeds. I may re-set my throttle linkage rod length one more time to see if it remedies my problem, but if it dosent i guess its not a big deal.

Thanks to everyone for the help.

Re: Surging at 3/4 throttle

Mon Oct 14, 2013 9:45 am

motoscott909 wrote:The only issue I can now find is that from low idle I have to move the throttle 2-3 notches before the speed picks up. After that I have the full range of engine speeds. I may re-set my throttle linkage rod length one more time to see if it remedies my problem, but if it dosent i guess its not a big deal.

All things considered, I wouldn't touch it again.