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Thread: fuel in my oil

  1. #1
    Newbie
    My Bike(s)
    1988 Yamaha Virago 750
    Posts
    3

    fuel in my oil

    I have a beautiful 1988 virago 750, It was a gift from my Dad (I guess Mom thought at 81 he was getting a little to old to ride it) Any how, I've been riding it for about a year and a half, mostly back and forth to work and a little joy riding now and then. The other day I went to start it and it didn't want to catch, sounded like it was grinding or catching. So I changed the oil and the oil I removed had gas in it (It was thinner then I thought it should be and it smelled of gas) I put the new oil in and it started right up, I went for a short ride and everything seems fine. My question is "How does gas get into my oil"? and is this something I need to worry about? any help is greatly appreciated.

    Eric

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  3. #2
    Just Won't Go Away !
    My Bike(s)
    several
    Location
    Buford, GA
    Posts
    5,197
    There is a tube that runs from the crankcase to a carb, to suck in and burn up the crankcase vapors. If the float bowl on that carb gets over filled, gas wil flow back down that tube into the crankcase.

    The fuel bowl can get overfilled it that cylinder is not firing, which is unlikely if the bike seems to be running OK. More likely causes are some junk in the fuel clogging up the shut off valve, or a leak in the float causing it to not shut off the valve when the bowl is full.

    Start with some good 'in the tank' carb cleaner, like SeaFoam, and keep an eye on it. If the oil level creeps up, or you smell gas, you may need to pull the carb and give it a good cleaning.
    You MUST obey the pug dog!


  4. #3
    Supporting Vendor
    Location
    La Quinta, Ca
    Posts
    754
    A little more explainion of why and what is most likely happening. The gas valve on the gas tank is either not being shut off or is not turning off. Some gas valves are manual shut off and some are vacuum shut off. Accodring the the gas tank exploded view, the gas shut off valve looks like it is vacuum operated.

    When the gas valve does/is not shut off, the fuel continues to flow. Since the gas tank is usually above the carbs, the pressure of the fuel is enough to over come the needle valves and floats in the carbs that regulate fuel level. This condition can worsen if the needles are old and worn.

    This causes the fuel to over flow in to the cylinders and/or the breather hose, which will seep pass the rings down in to the crank case/ transmission and down through the breather hose.
    Last edited by Blade; 06-28-2009 at 10:59 PM.

  5. #4
    Just Won't Go Away !
    My Bike(s)
    several
    Location
    Buford, GA
    Posts
    5,197
    I seem to recall the Virago having a fuel pump, not a gravity feed system. But maybe that was just the 1100, not the 750.

    Either way, if the float bowls overfill the problem is the float or float valve, as they should be strong enough to shut off the fuel flow even if the petcock does not shut off- they have to shut off the fuel flow when the petcock is open when the engine is running, so they should shut of the fuel flow when the bowl is full when the engine if off also. So bad float or dirty valve is still my diagnosis. But do double check the vacuum operation of the petcock- just suck on the hoses and see if the petcock opens and shuts. The float valves may be just leaking a little bit, so if the bike sits for a long time between uses and the petcock is not shutting off, you are getting the extra fuel one drop at a time. Fix both- it wil only get worse, until the bike will not run right from the fuel bowls overflowing all the time.
    You MUST obey the pug dog!


  6. #5
    Fourth gear and illegal
    My Bike(s)
    2008 Suzuki DL1000
    Location
    North Coast of Ohio
    Posts
    711
    Ok, what if it's a fuel injected bike? I noticed on my last oil change that the used motor oil smelled like gasoline.

  7. #6
    Newbie
    My Bike(s)
    1988 Yamaha Virago 750
    Posts
    3
    Thanks to all! I feel a lot better now! The bike had been sitting for about 2 weeks and I flooded it trying to start it a couple of days before I changed the oil. I appreciate everyones help!

    Now if anyone has any tips on bleeding the front breaks....I've been working at it on and off for a couple of days and I still have bubbles and no front breaks, I'm thinking of disconnecting the calipers and raising the lines and all up above the master cyclinder in the hope that the air bubble migrate up to the calipers.

    Once again, thanks to all.

  8. #7
    Just Won't Go Away !
    My Bike(s)
    2010 Hayabusa... a black one... the fastest colour
    Location
    Perth WA
    Posts
    5,145
    Quote Originally Posted by PerfectStranger View Post
    Ok, what if it's a fuel injected bike? I noticed on my last oil change that the used motor oil smelled like gasoline.
    Good question....If my memory serves correct the fuel system on an injected engine is continuously pressurised...I would suspect a clogged injector/carbon build up...but this is only a guess. Might also have a fuel vapour venting system from the motor that may be faulty...if possible check out the fuel/emission system diagram.

    Good luck
    Smoke me a kipper I'll be home in time for breakfast

  9. #8
    Fourth gear and illegal
    My Bike(s)
    2008 Suzuki DL1000
    Location
    North Coast of Ohio
    Posts
    711
    Thanks. I'm not going to fool myself into thinking I can do serious wrenching/diagnosis on the bike. Mechanic will have to take a look at it for me.

  10. #9
    Supporting Vendor
    Location
    La Quinta, Ca
    Posts
    754
    I use a Mity-Vac to fill the line with fresh brake fluid. Once I think they are close to solid fluid, I bleed the rest of the way using the old method.

    Loosen the bleeder nut and then lightly snug back down. Then pump the handle/foot lever until I feel a little pressure, then holding the lever/foot pedal in the braking position I crack open the bleeder nut to release the pressure. Then before releasing the handle/foot lever, I snug the bleeder nut back down.

    I repeat this until I have clear brake fluid coming out and good brake pressure. Once this is done, I will tie the front brake lever about half way back and leave over night. This will allow any remaing air to escape in to the master cylinder resivor. Not much you can do to do this to the rear brake.

  11. #10
    Newbie
    My Bike(s)
    1988 Yamaha Virago 750
    Posts
    3

    Thanks Bill

    On my bike the front and back brakes are indepentant of each other, so just the hand lever, I will try the mity-vac.

  12. #11
    Clunked into first gear
    My Bike(s)
    black and silver suzuki m50
    Location
    MN
    Posts
    211
    another way to bleed the brakes is to find a clear hose that fits on to the brake bleeder. so, you stick that on there and put the other end of the hose in a brake fluid container. then crack it open and pump the brakes. it will push the fluid and air out of the line, and the only think it can suck back in is brake fluid. just do that untill no more air comes out. you could also have blow by from the rings if gas is getting into the crankcase.

  13. #12
    Newbie
    My Bike(s)
    '07 honda crf80f
    Posts
    1
    My son has a '07 Honda CRF80F dirt bike that is having similar problems. It sat up for a while at my father in laws place and we went and picked it up to go ride and it would start cutting out when it was opened it up. I started by cleaning the carb out with cleaner. I put it back together and it would crank up fine and I could rev the engine without it cutting out with the air breather disconnected from the back of the carb. So I put the breather back on and it went back to cutting out when we tried to rev the motor. As a next step I pulled the air filter just to check it out, wasn't in too bad of shape at all. I left it off and tried reving the motor and it would still cut out. I then noticed oil coming back out of the air box. I checked the oil and it was full of gas. I drained it, refilled it with fresh oil and fired it up. After about a minute of running, I shut it down and checked the oil and it had gas in it again. It has a tube running out of the crank case into a black cylinder and a tube that runs from the black cylinder to the breather tube. This explains why it runs fine with the breather disconnected from the carb, but not with the breather connected and the air filter out. Oil is not coming back out of the air box any more so I suspect that was happening because there was so much fuel down in the crank case.

    With that said, do you guys think it's the float sticking that could be causing it to over fill and get gas down in the crank case? Is there anything I can do to try and narrow down what may be happening in the carb causing it to happen? I'm not much of a mechanic, know a few things from standing over my dads shoulder growing up. I would appreciate any advice on where to proceed to next in trying to fix the problem.

  14. #13
    U.B's LoveChild
    My Bike(s)
    '08 Suzuki M50,1975 Goldwing,1982 Silverwing
    Location
    Hensley, Arkansas
    Posts
    1,089
    Quote Originally Posted by DADS88 View Post
    I have a beautiful 1988 virago 750, It was a gift from my Dad (I guess Mom thought at 81 he was getting a little to old to ride it) Any how, I've been riding it for about a year and a half, mostly back and forth to work and a little joy riding now and then. The other day I went to start it and it didn't want to catch, sounded like it was grinding or catching. So I changed the oil and the oil I removed had gas in it (It was thinner then I thought it should be and it smelled of gas) I put the new oil in and it started right up, I went for a short ride and everything seems fine. My question is "How does gas get into my oil"? and is this something I need to worry about? any help is greatly appreciated.

    Eric
    Go over to Viragotech website. You will find all the info you will ever need for the Virago. The problem you are having is quite common on the Virago line.
    If you can't dazzle 'em with brilliance,Baffle 'em with Bulls!!t!

    Roadburner Street Pro's on my M http://www.youtube.com/watch?v=Hf0IYPcoiVc


 

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