Gas in Oil with manual petcock

[Myles Best]

Hey guys, newb to the carb life but not the wrench life. Picked up a DRZ that has the JD jet kit with a manual petcock. When I picked it up, it had a hard time starting and was tuned poorly. I tuned the carb and it still hard a hard time starting for a bit, but recently, today, starts like gold and easy (with no changes). The gas smell has gotten a bit worse, but again, now it's also starting like gold so I feel like it's "fine" now? So with a manual petcock, I know it's not the vacuum problem, but it could be the float valve? Is there any easy way to tell if it's the float valve other than replacing the oil and see if it's happening again? And then is there any good "up to speed" on carbs? Like, one, I'm curious how the hell fuel and oil get mixed up like that and why. And two, understanding if the float valve needs to be replaced or if this was just a mistake of the manual petcock not being turned off after every ride. Or would it be, if the valve was working I wouldn't have to, but turning it off would be an insurance policy from whatever happened? So yeah I've seen a lot of "oh when gas is in there it's the petcock or the float valve" But having a manual petcock I'm not sure how to take that, esp since none of those posts seem to explain how/why it mixes up. Anyway, off to youtube to go find some carb videos, but wanted to post here first!

edit: 2003 DRZ S

Edited August 5, 2020 by Myles Best

[Tony Wyp]

12 minutes ago, Myles Best said:

Hey guys, newb to the carb life but not the wrench life. Picked up a DRZ that has the JD jet kit with a manual petcock. When I picked it up, it had a hard time starting and was tuned poorly. I tuned the carb and it still hard a hard time starting for a bit, but recently, today, starts like gold and easy (with no changes). The gas smell has gotten a bit worse, but again, now it's also starting like gold so I feel like it's "fine" now? So with a manual petcock, I know it's not the vacuum problem, but it could be the float valve? Is there any easy way to tell if it's the float valve other than replacing the oil and see if it's happening again? And then is there any good "up to speed" on carbs? Like, one, I'm curious how the hell fuel and oil get mixed up like that and why. And two, understanding if the float valve needs to be replaced or if this was just a mistake of the manual petcock not being turned off after every ride. Or would it be, if the valve was working I wouldn't have to, but turning it off would be an insurance policy from whatever happened? So yeah I've seen a lot of "oh when gas is in there it's the petcock or the float valve" But having a manual petcock I'm not sure how to take that, esp since none of those posts seem to explain how/why it mixes up. Anyway, off to youtube to go find some carb videos, but wanted to post here first!

Take the fuel line off the petcock. Tip out any residual petrol in the line.

1. Suck on the line to see if petrol comes from your carb bowl, into your mouth. If it does, your 'valve'  is faulty.

....or 2.  Blow into the line. If you can blow into it, the 'valve' is faulty.

3. Check your float level.

Edited August 5, 2020 by Tony Wyp

[Myles Best]

Sweet that makes sense, the valve could let me blow into it if the float chamber is not "full"? But seems like that would be unlikely. Then the reason it might have been having trouble before was because the float chamber was overfilled and messing with the vacuum pull in the carb? Then if I left the petcock on after I turned off the bike, if the valve isn't working, gas will slowly keep going to the float chamber and then drip into the carb, into the engine, pass the rings since it's not expoding and then get into the oil track? So simply turning off the petcock after flushing the oil should "fix" it, but I should change the valve just as another insurance policy.

[Tony Wyp]

49 minutes ago, Myles Best said:

Sweet that makes sense, the valve could let me blow into it if the float chamber is not "full"? But seems like that would be unlikely. Then the reason it might have been having trouble before was because the float chamber was overfilled and messing with the vacuum pull in the carb? Then if I left the petcock on after I turned off the bike, if the valve isn't working, gas will slowly keep going to the float chamber and then drip into the carb, into the engine, pass the rings since it's not expoding and then get into the oil track? So simply turning off the petcock after flushing the oil should "fix" it, but I should change the valve just as another insurance policy.

You should always turn a manual petcock off.

If the valve is faulty it will let fuel into the oil. I dont think there is any other way this can happen.

Vacuum petcocks are great.

[mmiguy2103]

you can easily bench test the carb with the float bowl off and test to see if the float needle is stopping the flow of fuel..  there is a o ring under the seat that wears out with our crappy ethanol fuels we have now. so sometimes it will bypass the needle and seat and sneak around the side of them.    I prefer a manual petcock as growing up with them on all my toys.  just shut it off after every ride and you know for a fact you wont have a issue.  its hard to say where your problem was with the petcock not being shut off or the float valve failing without a bench test.      the vacuum petcocks are a known fail not just with our DRZ's but with most of every bike that has them. they wear out with our ethanol fuels faster than originally anticipated. then they allow your tank to just empty right into your engine.  with the stock carbs they have no overflow on the carb,

 

 so yea double check your petcock is working properly by removing the fuel line and seeing if anything leaks by with it in the off position,  and check your float needle and seat/ o ring and replace is necessary 

[1hp]

the thing is that the crap stock carb does not have an overflow tube.

[TexasSergio]

On 8/5/2020 at 5:20 AM, mmiguy2103 said:

you can easily bench test the carb with the float bowl off and test to see if the float needle is stopping the flow of fuel..  there is a o ring under the seat that wears out with our crappy ethanol fuels we have now. so sometimes it will bypass the needle and seat and sneak around the side of them.    I prefer a manual petcock as growing up with them on all my toys.  just shut it off after every ride and you know for a fact you wont have a issue.  its hard to say where your problem was with the petcock not being shut off or the float valve failing without a bench test.      the vacuum petcocks are a known fail not just with our DRZ's but with most of every bike that has them. they wear out with our ethanol fuels faster than originally anticipated. then they allow your tank to just empty right into your engine.  with the stock carbs they have no overflow on the carb,

 

 so yea double check your petcock is working properly by removing the fuel line and seeing if anything leaks by with it in the off position,  and check your float needle and seat/ o ring and replace is necessary 

I just had this problem with my 05 DRZ400SM. Tried to start it and it barely turned over. Pulled the plug and its wet with gas. Cranked it and shot gas out the cylinder. Checked the oil, full of gas. I ordered a new needle and seat, comes all together with the o ring that leaks.I guess you can replace just the o ring if you can find the right one. Next is a manual petcock. Have hated the vacuum ones, they always start leaking after a few years.  

[shuswap1]

That nasty little O-ring under the float needle valve is the number one culprit, it hardens and leaks. Sizes are listed in the FAQ at top of page, less than $.50 cents. I am still using the original float valve assembly in my 2003, they rarely leak. I also installed a manual petcock and use it religiously.

[bumtarder]

Manual petcock or not,the o-ring under the float needle seat is going to deteriorate and cause fuel to go into the crankcase,especially if the manual fuel valve is left on when not riding as compared to the vacuum type.It's only a matter of scale.

[Topaz]

29 minutes ago, bumtarder said:

Manual petcock or not,the o-ring under the float needle seat is going to deteriorate and cause fuel to go into the crankcase,especially if the manual fuel valve is left on when not riding as compared to the vacuum type.It's only a matter of scale.

why? What if you have a manual petcock and remember to shut it off every single time? Also, you could leave the bike running after having shut off the petcock so the bike burns the remaining fuel in the carb jets and lines and the o-ring would remain dry. That way, the o-ring should last much longer. 

That is what I was doing in my last carbureted bike. However, that petcock had the auto shut off and a manual shut off, so it would give you both options. 

 

[bumtarder]

Ok,that's fine.What you are effectively doing is draining the float bowl.What I'm alluding to is the o-ring in the Mikuni float needle seat will still deteriorate regardless and cause problems but to a lesser degree with a manual petcock.The type of petcock is not the core problem here but the o-ring under the seat.If you're shutting the manual fuel valve off every time and/or running the bowl dry the fuel will not leak past the seat as much but the core problem can still exist but it is controlled.The failure of the vacuum petcock can make it much worse but still,two things usually have to occur for it to happen.

[Topaz]

oh, got you!

So you say the o-ring will deteriorate even if it's not in contact with fuel? I thought the consensus was that it was the ethanol fuel the root cause of the o-ring decaying. 

[bumtarder]

It's pretty much always in contact with fuel as that is where the fuel enters the carburetor so it will eventually deteriorate and go bad. Even if the fuel valve is closed and you run the motor until it stalls there is still residual fuel left in the float bowl most of the time.