Engine Surging at WOT

[GBHRPS]

Gentlemen,

I have an older Z Force 48 that has been repowered with a B&S 26 hp engine, instead of the B&S factory 22.

No problems at starting, low or medium throttle, but at high throttle settings the engine will speed up and slow down at one second intervals. Its not so noticeable when cutting grass, but with the PTO disengaged and running across the lawn, you can feel the surging as the you are moved slightly forwards and backwards in the seat.

Any ideas?

Gene

 

[ruffdog]

It sounds like it may be running lean at wot (main jet circuit). I would pull the carb float bowl and look for evidence of any water. I would look at the main jet for any debris in it and check fuel flow from the fuel line. Is the outlet in the tank blocked? Is the filter, pump, line plugged? Water will sit at the bottom of the bowl where the jet gets its fuel. Don't just clean the jet either. You have to check the distribution tube that goes to the throat of the carb too and make sure the air bleeds are clean. Is it a OHV engine? How many hours since the last valve adjustment?

 

[GBHRPS]

ruffdog,

Thanks for the suggestions! It'll take some time until I get get back to the Cub. May need to cut the grass one more time this year before it goes into storage. I'll try to make the time to drain the carb, etc., before that happens. I'll let you know how it works out.

 

[Hill Billy Bob]

My LT1050 did something similar to what you are describing one time......turned out to be the transmission drive belt had a chunk about 5" long missing from the inside of it. Outside edge of belt and the cords held together, but that missing chunk from the inside edge caused the belt to slip a bit as it went around the pulleys, which in turn gave me that surge feeling.....Hill Billy Bob