pumper carb and cylinderwash?


Mar 19, 2001
What do you guys think, I have thought about this ever since installing a pumper on my xr4. Is raw fuel washing the oil off my cylinder? Any research, opinions? I would really hate to be toasting my engine prematurely, but I love the performance! What do you think?


Mi. Trail Riders
Dec 6, 1999
Man, I'll bet that engine totally shot by now! :scream: I'll get you an address to send me your bike with the toasted motor! ;)

The function of an oil control ring is to scrape down oil from the cylinder wall. I wouldn't think you'd be causing any damage to your engine with the pumper carb. There'd be a whole bunch of toasted automobile engines over the last 40 years, as well as a bunch of toasted Yamaha 4-strokes (hey - watch the cheap shots now!) if accelerator pump gas caused a problem with the cylinders.


Aug 22, 2000
Fuel wash is caused by an excessive amount of fuel in the fuel/air mixture.

The pumper carb is actually more efficient at metering fuel in the cycle, so there's less likelihood of fuel wash.

Of course, it's always possible to have too much of a good thing - so I guess if you increased the size of the nozzle, and the throw of the rod on the pump, then also increased the size of the mainjet and moved the needle to a higher position--you'd have problems. Of course, the bike would run like crud too!

Basically, fuel wash is easy to avoid - if the bike runs well and doesn't exhibit excessively rich symptoms - this is ONE thing you'll never have to worry about.

Even a bike jetted relatively rich (say 2 sizes too large on the mainjet) will not fuel wash - it'll just run like crud!


N. Texas SP
Feb 19, 2000
I gues if you sat on the bike while it is not running and repeatedly twisted the throttle, you might get some cylinder wash, but the bike probably would not start, so any damage would be negligible.:)

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