Surging engine.

[Posco]

Got my Cub back from a local guru and noticed the engine rpm seems to surge up and down. He rebuilt the carb...new float, etc. and cleaned up the governor among other things. It seems to idle just fine at an even rpm but when I apply throttle while I'm plowing it's up and down, up and down. My understanding is the governor will modify rpm when a load is applied but this seems to surge whenever rpm is up whether under load (plowing) or not. Normal?

[Eugene]

Not normal. Could be fuel flow (carburetor), governor adjustment, or linkage adjustment. Start with the linkage adjustment.

You can test by separating the governor from the carburetor and operating the carburetor by hand.

Caution, do not let the engine over speed, run away, before you get a chance to control/operate the carburetor by hand.

[gitractorman]

Check to make sure the throttle to governor linkage is not rubbing against the engine block. Pretty common occurance and will cause exactly what you're describing. It's easy to bend this when taking the carb off, and not realize that you've pushed it towards the engine.

Also, make sure that all the linkage throughout the governor/carburetor is all moving/sliding freely. If it's bound anywhere it can cause this.

Next, double check that the carb to manifold bolts are tight, as a vacuum leak could cause this. Again, if someone else did the work, they may have stripped the bolts trying to tighten the carb.

Those are my thoughts.
Bill

[Steve Butram]

Did you sync the governor to the carburetor? Via the carburetor linkage

http://www.cleancomputes.com/Cub/Blue%2 ... age-28.jpg
http://www.cleancomputes.com/Cub/Blue%2 ... age-29.jpg

[Connecticut Calvin]

I agree with all the above. The linkage on my Cub was not only maladjusted it was also bent and stuck on the block. When I first got my Cub it had a severe timing issue. Once that was fixed it started fine but my engine surged to dangerously high RPMs because of the linkage problem. Sure drove fast though!

[Posco]

Thank you to all who replied, I really appreciate it. It's been cold, snowy and I'm working a lot of hours so haven't had the time or inclination to take a good look at it yet but I did notice the outdoor temperature seems to have an effect. I'm wondering if there might be something gummed up that stiffens in the colder weather. It operated normally when it was above freezing but today with the weather in the mid teens, it did the surge thing again.

I'll let you know what I find when I get a chance to give it a good look. Thanks again!

[Eoghan]

if the air cleaner was filled with heavy weight oil or water has gotten in it can make the tractor run pretty lousy in the cold too.

[Posco]

if the air cleaner was filled with heavy weight oil or water has gotten in it can make the tractor run pretty lousy in the cold too.

I'll check that. Thank you!

[Posco]

I pulled the linkage from the carb to the governor and the rpm remains constant at high or low throttle so it's not a fuel starvation issue. I pulled on the governor linkage with the engine running and it would fight me. When I pull, it pulls back.

[Bus Driver]

What you describe sounds normal. When parked and running at no load, the engine requires much less fuel than when doing work (plowing). My first step would be to (really, really) clean the high speed jet.

[Don McCombs]

I pulled the linkage from the carb to the governor and the rpm remains constant at high or low throttle so it's not a fuel starvation issue. I pulled on the governor linkage with the engine running and it would fight me. When I pull, it pulls back.

Have you adjusted the linkage in accordance with the recommendations above?

[Posco]

I pulled the linkage from the carb to the governor and the rpm remains constant at high or low throttle so it's not a fuel starvation issue. I pulled on the governor linkage with the engine running and it would fight me. When I pull, it pulls back.

Have you adjusted the linkage in accordance with the recommendations above?

I tried opening the link earlier in the day with no luck or time. I'm going to try opening it again.

[Posco]

I adjusted the rod connecting the carb and the governor as per directions in the link and it helped a bit but I seem to have lost quite a bit of available throttle. There seems to be a fair amount of slop in the connecting rod leading over to the governor. I can articulate the rod leading over to it back and forth before it engages. There is a fellow on ebay who has reconditioned governors for sale for $148.00 plus a fifty dollar refundable core charge. Thoughts?

[Rick Spivey]

There is a key and keyway that is internal to the governor, and the rod that goes across the front of the engine is indexed to the governor by this. It is common for that keyway to wear, causing slop, and lost motion in the throttle control. There are some fixes if you search on here, and/or the rebuilt governor "may" not have the same issue. I would want confirmation of that before I purchased one.

[Posco]

There is a key and keyway that is internal to the governor, and the rod that goes across the front of the engine is indexed to the governor by this. It is common for that keyway to wear, causing slop, and lost motion in the throttle control. There are some fixes if you search on here, and/or the rebuilt governor "may" not have the same issue. I would want confirmation of that before I purchased one.

Thank you. That is exactly what I'm experiencing. As I mentioned before, a local tractor 'guru' did a bunch of work for me but somehow he overlooked this issue. Odd, in that I asked him specifically to go through the governor and the carburetor which he said he did. Time for a new 'guru'.