Cub Lo Boy 185 engine surge question

[mlip]

Hello,

My 1974 LoBoy 185 has started surging when run hard in 85 degree plus temps. Works fine without load but once any load is applied to the engine the rpm "hunts". Oddly enough giving it a little choke seems to help. Any ideas?

Mark

 

[Paddy]

Could be govnerner issue.

 

[RobertN]

Weak springs in the governer, slop in the governer linkage, and maybe governer adjustment.

Check the manual; there should be an adjustment on the governer. I have done it on my Farmall-A. Although yours is 30 years newer, I believe the governer is very similar.

I had a spring break inside the governer; all it would do is idle. When I replaced the spring I had to make adjustments.

 

[Soundguy]

Probably a gov issue like the others said.. but i would investigate the carb as well... might have a fuel shortage issue.. that will make an engine surge under load. Choke provides more manifold vacume to help pull the fuel...

Soundguy

 

[mlip]

Thanks, the choke helping the issue has me suspicious that its somehow fuel/vacuum related. Plus, it only seems to happen when at full op temp on hot days under load.....I will read the manual relative to the governer tho....Mark

 

[MarkStewart]

Maybe vapor lock? Is the fuel line routed near anything really hot?

 

[Nat]

I would bet on a dirty carb. I have had the same problem before and it has always been trash in the carb. You may be able to fix it as easily as starting it up , pulling the throttle wide open and spraying carb cleaner in the throat. then again you may have to take the carb apart, but I would try the spray first.
Most any govenor problems start slowly and continuly get worst, or a spring breaks and it won't rev up. Buy some carb spray. Later, Nat

 

[Soundguy]

My cub has the updated later zenith carb on it... When they clog.. they clog... I rebuilt mine on the kitchen table with a kit from napa in about 15 minutes.. Replaced the flaot needle and seat.. but shouldn't have.. the new needle does not fit the seat as well as the old needle and seat... had to finagle with it to work....set it at about 1 turn on the main and 1 turn on the idle, and it fired on the first stroke..

Soundguy

 

[mlip]

thanks....I'm going to go after the carb first, really dont want to mess with the governor until I've eliminated some other things first...thanks for the help

 

[mlip]

this is a long over due followup, but in case someone else has the problem, I wanted to document it here.

The surge went away after I used compressed air to clean out the radiator. Apparently the partial blockage between the radiator fins combined with lifting heavy loads in 85 degree plus weather was enough to reduce heat transfer just sufficient to push the engine operation over the edge into instability. The radiator looked OK on first inspection, but a close look at the fins revealed that light dust had collected on them and in some instances blocked airflow.