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Gas in oil

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I've been getting gas in my oil and can't for the life of my figure out where it's coming from.  I've changed the oil multiple times, installed a manual petcock, cleaned the carb, and run the carb almost dry after each ride.  The oil level seems to stay constant (I burn some at idle when I give it a quick rev), but it still has a strong smell of gas.  Would blow by or bad valve seals cause this?  I always thought that the gas would ignite before making its way into the crankcase?

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You have the Mikuni carb I'm assuming . It has an o-ring under the needle valve that is what causes all the gas leaking issues with these bikes . A person often only notices it when the stock petcock also fails . If you shut the petcock off and run it for a bit there shouldn't be an issue , no need to run it dry . If you do that and it's still getting in I'd check for the manual valve leaking , I've rebuilt several of mine every couple years because they start leaking .

 

 

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Edited by jjktmrider

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2 minutes ago, jjktmrider said:

You have the Mikuni carb I'm assuming . It has an o-ring under the needle valve that is what causes all the gas leaking issues with these bikes . A person often only notices it when the stock petcock also fails . If you shut the petcock off and run it for a bit there shouldn't be an issue , no need to run it dry . If you do that and it's still getting in I'd check for the manual valve leaking , I've rebuilt several of mine every couple years because they start leaking .

Thanks for the reply, I have the FCR carb.  The old vacuum petcock wasn't leaking, but I replace it anyway with a manual.  I've checked the needle in my carb and it seems fine; even though I don't believe it's possible to change out in the FCR because it's press fitted.  I thought that I could rule out the needle by emptying the bowl when I park, but it's still getting gas in the oil.

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2 minutes ago, ohiodrz400sm said:

The seat is not press fit. It's retained by a screw.

Sent from my XT1650 using ThumperTalk mobile app
 

Yes, there is a screw holding it in, but it doesn't just fall out.  I've seen numerous threads about people marring the surface and housing towards the point of junking it.  That's a last case scenario in my book, but a manual petcock and draining the carb after each ride should have identified the valve, right?

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7 minutes ago, ohiodrz400sm said:

The O-ring is probably harden and it's just stuck.

The accelerator pump is another way to flood it. Are you, or anyone else, twisting the throttle while the bike is off?

Sent from my XT1650 using ThumperTalk mobile app
 

Yup, I've made sure not to twist the throttle while not running, since it's a pumper carb.  I learned that the hard way after I found out what gas tastes like while cleaning the carb.  I'm just out of ideas now of what it could be.

Edited by Shaz

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I don't think the o-ring is much of an issue on the fcr , but can always do the same as the Mikuni . Have you verified after it sits for a couple hours/days that the bowl isn't full again ? Meaning if things were still/again leaking while it sits . To put a bunch of gas in the oil while it's running is pretty hard to do , you would have to be really dumping excess fuel down its throat and then it would have running issues . Any blowby vapors would/should be burnt up as the bike is running , not much of a way to actually add volume in the oil .

I suspect your leaking as it sits , doesn't matter if it was run dry to start with , it can still refill by those bad O-rings( but very odd in the fcr).

 

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26 minutes ago, jjktmrider said:

I don't think the o-ring is much of an issue on the fcr , but can always do the same as the Mikuni . Have you verified after it sits for a couple hours/days that the bowl isn't full again ? Meaning if things were still/again leaking while it sits . To put a bunch of gas in the oil while it's running is pretty hard to do , you would have to be really dumping excess fuel down its throat and then it would have running issues . Any blowby vapors would/should be burnt up as the bike is running , not much of a way to actually add volume in the oil .

I suspect your leaking as it sits , doesn't matter if it was run dry to start with , it can still refill by those bad O-rings( but very odd in the fcr).

 

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When I still had the manual petcock, I disconnected the fuel line going to the bowl and attached a water bottle to collect any leaking gas.  After 24 hours there was nothing.  If it's not coming from the petcock, where else could it be?

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If your oil level isn't going up I'm thinking it's just a case of paranoia , maybe it smells stronger than it should , maybe it smells normal , I know mine often has a hint of gas smell , more from the combustion process and being a little rich jetted , may be the same with you . Then with a bit more blowby than normal it will smell worse , but not much of a chance it will add volume and thin the oil to where it's bad , at least not without running issues.

 

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Edited by jjktmrider
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On 7/31/2017 at 0:34 PM, jjktmrider said:

If your level isn't going up I'm thinking it's just a case of paranoia , maybe it smells stronger than it should , maybe it smells normal , I know mine often has a hint of gas smell , more from the combustion process and being a little rich jetted , may be the same with you . Then with a bit more blowby than normal it will smell worse , but not much of a chance it will add volume and thin the oil to where it's bad , at least not without running issues.

Guys, I'm bringing this back up because I still can't find the issue.  I determined that the carb is not leaking onto the piston while idle, since I run the carb dry after each time I ride.  The smell is definitely coming from when I ride.  Could a blocked breather somewhere possibly cause this?

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yup , Outside of an overly rich jetting , no way for gas to get down in the motor while running. Blackstone Labs oil analysis will maybe show a small amount of fuel saturation , as is pretty common in the drz(from what I remember being said in that thread) . There isn't raw fuel running into the oil , diluting it horribly . You should have that black box on the right side just inside an above the exhaust pipe with the hose coming in the bottom from the crankcase , and one going out into the airbox. That is what gets rid of fuel vapors as the motor runs hot

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34 minutes ago, jjktmrider said:

yup , Outside of an overly rich jetting , no way for gas to get down in the motor while running. Blackstone Labs oil analysis will maybe show a small amount of fuel saturation , as is pretty common in the drz(from what I remember being said in that thread) . There isn't raw fuel running into the oil , diluting it horribly . You should have that black box on the right side just inside an above the exhaust pipe with the hose coming in the bottom from the crankcase , and one going out into the airbox. That is what gets rid of fuel vapors as the motor runs hot

Is it not possible to have enough ring blowby that during the compression stroke the gas mixture gets into the oil?  

 

I checked the black box and all the inlets, and none were obstructed.  Could blow through all of them.  I guess I'll check the jetting in the FCR today.

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Is it not possible to have enough ring blowby that during the compression stroke the gas mixture gets into the oil?  

 

 

 

 

 

 

 

I checked the black box and all the inlets, and none were obstructed.  Could blow through all of them.  I guess I'll check the jetting in the FCR today.

No, raw fuel would not slide by the rings in liquid form while running. Check jetting and report back.

 

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Just pulled the carb.  My jet sizes are:

Main jet - 165

Slow jet - 42

Starter jet - 80

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The float seems fine at 8mm.  I did notice a crack on one of the jet inlets.  Could this cause my issue?  The jet seems like it screws in deep enough for the crack not to affect it.

 

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Edited by Shaz

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