Engine revving up SOLVED

[markh28]

Got my Chrysler 7.5hp going. Only problem is it keeps revving up then slowing down, revving up and slowing down. Just like someone is twisting the throttle on a motorcycle up and down. I have always used the term "loping" but I searched for that here and found nothing. Other than that the motor is firing good and shifing good. Im sure its something in the carb. But what causes this?

 

[roscoe]

Re: Engine revving up

Re: Engine revving up

Likely a sticky float in the carb.
Time to clean her out.

 

[markh28]

Re: Engine revving up

Re: Engine revving up

OK, cleaned the carb thouroughly (twice). Bought a carb gasket/seal kit, put that in. Still loping. Ordered a carb repair kit that included the needle and seat, installed that, and it still lopes like it did the day I brought it home. One interesting thing, is that before I changed the needle and seat, the float appeared to be stuck when I turned the carb upside down, and when I touched it, it dropped all the way back down. But once I installed the new needle/seat the float seemed to operate more freely, and I thought I had it whipped there, but it still has the lope.

I am setting the float according to the Chrysler repair manual which I have. 1/8" and 5/16".

I also opened up the fuel pump housing and the diaphram looked ok and intact, although it was a little bit wrinkled but I didnt think it would make a difference.

What else could this be? Its almost like its not related to the carburetor because after all the cleaning and work, it still does the exact same thing. Could it be ignition related?

One last piece of information, the carb is a Walbro LMB-215. If you order a carb kit for a 1983 Chrysler 7.5HP you will get the kit for the Tillotson carb (learned that one the hard way)

Any suggestions are appreciated!

 

[CharlieB]

Re: Engine revving up

Re: Engine revving up

A small air leak at ir after the carb will cause an engine to surge, search or lope, as if the governor is set too tight.

Running at an idle, Test using a spray can of good carb cleaner, a flamable solvent, lightly spray the base of the carb, intake, and the engine cases at the parting lines. any leak will pull in the solvent and increase engine speed.

 

[markh28]

Re: Engine revving up: SOLVED

Re: Engine revving up: SOLVED

Just updating the thread so hopefully this can come in handy for someone in the future. I had a couple spark plugs sitting around that I was going to get to after I got the loping or surging to quit. So I decided to just change those to see what happened. Dropped in the new plugs, pulled the rope and she took off like a brand new motor. No loping, no surging. It was the plugs.

Now I just need some minor carb adjustments from messing with it so much but thats no big deal.

CharlieB, followed your advice and sprayed the carb cleaner around the intake and it did not increase engine speed, however, when I took out the bottom plug it sure wasnt in there very tight, which I am thinking caused an air leak which caused the surge. Thanks to everyone here on this thread for the help!

Now....onto my next project motor...but thats a topic for another thread.