[JJT3]

Rebuilt the carb on my 8hp Tecumseh/Troy Bilt snowblower this year. Using fresh high test with Startron. After 45 minutes of run it "bogs" down, then runs up in rpm, then acts like it's going to stall. Have removed gas cap to see if there is a venting issue. Shut it off, take a 5 minute break and it will start up and run for another 10 minutes flawlessly, then act up again. Not sure where to start, any suggestions?

 

[Mark / Ohio]

Couple thoughts..

Carburetor icing up? Do you have all the original plumbing on the intake? Could some snow be sucking into it?

Vapor lock? Is the fuel line where it could be getting hot?

 

[JJT3]

Thanks Mark, tried something today. Ran until it started bogging, removed the gas cap and waited while running. Engine smoothed out, put cap back on and worked the machine for a few minutes, then it started again. Maybe the vent in the cap is icing up? Changed the plumbing this year with carb work.

 

[bwdbrn1]

Sounds like you might have found your problem. I've had caps that I leave sitting in carb cleaner for awhile, then blow air through them. Some I just plain replaced.

 

[JJT3]

Thanks all. Snow again today. This time I left it loose, never skipped a beat. Did have someone suggest that the coil might be breaking down when it gets hot. Will give it a long workout this weekend and see. This cap has a rubber vent system that must keep moisture out, with a rubber "cone" in the center. Must be special for snow blowers.

 

[Mark / Ohio]

Thanks all. Snow again today. This time I left it loose, never skipped a beat. Did have someone suggest that the coil might be breaking down when it gets hot. Will give it a long workout this weekend and see. This cap has a rubber vent system that must keep moisture out, with a rubber "cone" in the center. Must be special for snow blowers.

I kind of doubt it would be a coil problem. Your comment "After 45 minutes of run it "bogs" down, then runs up in rpm, then acts like it's going to stall." has lean mixture written all over it in my mind.

Maybe the rubber due to age and cold is getting a little stiff and not doing its job?

 

[JJT3]

Thanks Mark and all. Sorry for the delayed response, that motor has gotten quite a workout this year. I'm running it with no more than 1/2 a tank of gas and the cap loose. Doesn't skip a beat, so will invest in a new cap when the weather permits. Thanks again!