Pressure in crankcase?
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  1. #1
    Senior Member kenfyoozed's Avatar
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    I rode my '99 tw around to get a fill for it, and when i stoped i noticed some oil on the ground. So I start to remove the fill plug thinking it had a dipstick.....ive found out now it doesnt and theres a sight glass..... but when i removed the plug there was a burst of air released as if the crankcase was underpressure. I assume this is not the way its supposed to be? What would cause this?

  2. #2
    Senior Member lizrdbrth's Avatar
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    If your crank case is overfilled (either with oil or gas/oil mixture as in the case of a sticking float) It is possible that air would escape if the piston was on the downstroke at shutdown. The filler cap would be a high point, trapping air.



    Other reasons include a clogged or capped off crankcase vent.



    Check your airbox. If it's full of oil you have issues to deal with before you run the bike.



    I can explain it to you, but I can't understand it for you.

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  3. #3
    Senior Member kenfyoozed's Avatar
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    Thank you for your help. I went out and removed air filter and there was no oil in the air box. I could see that the passge from the breather tube into the airbox was clogged. Looked like what isee alot around this area.... some type of spider builds a nest out of dirt, almost like a dirt bobber wasp. I cleared the passge, but the breather tube was just an easy tug to remove it. I wouldnt think the blockage cause that much back pressure with out blowing off the tube? But what do i know? stranger things have happened to me. I know this bike needs a good cleaning so ill change fluids and clean carb and airfilter. The oil fill tube does not have an o-ring so i need to add that to my list. In searching I ran across threads about seafoam in the cylinder. I have to do more research to see if i should try this as well.

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  5. #4
    Member -Jake-'s Avatar
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    dumb question but was the bike running when you removed the fill plug?

  6. #5
    Senior Member kenfyoozed's Avatar
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    No it wasnt runing but i had just shut it off walked across the room and got a tool to remove the fill plug. It was really torqued down to stop the leaks since it didnt have an o ring in place.

  7. #6
    Senior Member assquatch20's Avatar
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    First, the crankcase vent is plausible, combine that with the sticking float theory and you definitely have pressure building up.



    However, after every oil change, you're supposed to get on the right side of the bike and look for a bolt around the rear-right corner of the cylinder. It's there to bleed the oil out after a refill. This might be your problem as you can get something like a vapor lock in the top end of the motor and a pretty bad failure if it's terrible enough. After an oil change, Loosen this bolt as the bike is running until oil seeps out a bit, then you should hopefully be free of pressure in the motor. I'm not sure it would have enough pressure to blow air out without wrecking the engine first, but it's possible I suppose. Anyhow, bleed that while it's running and see what happens after some riding.

  8. #7
    Senior Member kenfyoozed's Avatar
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    You guys are right on the money. if i did my research right it takes 1000cc of oil, but when i drained i got back almost 2000cc. upon further reaseach and looking at some pictures, you could see the carb had problems at some point. So i dove into dismantling the carb and in the proccess i drove a screwdriver about an inch into my thumb/palm area. So working on it is done for the night.

  9. #8
    Senior Member assquatch20's Avatar
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    Replace the float bowl screws with allen heads. Even if you don't need it, order jets and a rebuild kit for the carb sometime in the future. You always need it eventually.

  10. #9
    Senior Member kenfyoozed's Avatar
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    I orderd the float valve seat and bowl gasket. I will replace the other parts soon enough. I just wanted to get back to square one before starting to really adjust anything. Thanks again for all the help.

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