Gas getting into crank case

[Daren Todd]

Ok guys. I got a conundrum I'm trying to solve for my in-laws. They have a Yamaha Grizzley 600 that they purchased a few years ago. Four wheeler is anywhere from 15 to 20 years old. Has probably been sitting for a couple years. Anyway, got it over to my house. Changed the spark plug. Cleaned the carburetor, then dropped the oil to change it.

Noticed when I drained the oil, it had a strong smell of gasoline. Did an oil and filter change on it. Installed the carb. Filled with gas, installed a new battery and got it running. Ran real smooth, had plenty of power. Put about an hour on it running around the yard. Thenparked it with the fuel shut off.

Started it a few more times, with loading it and unloading it after I returned it to my in-laws. Did a couple hill climbs with it, and maybe lauvhed it a couple times for a suspension test Each time I shut it down, I shut the fuel off, and double checked the oil level before starting. Oil level never went up.

Wheeler sat for a couple days, then my mother in-law took it out for a spin yesterday. Ride lasted for about 5 minutes, then it bogged down on her and quit. That's when She noticed some gas dripping.

So I swung by yesterday afternoon and double checked it. Found the crank case full of gas to the point it was blowing oily gas out the crankcase vent.

So the million dollar question. How is the gas getting into the crank case while running?

 

[Bulldog777]

Not sure how, but i had a Yamaha 3 wheeler that would do the same thing if you didn't shut the gas off.

Sent from my SM-G955U using Tapatalk

 

[100 td]

down, That's when She noticed some gas dripping.

From where?
I don't know your engine or carby but if it has a crankcase pressure pulse pump to feed the carby it probably has a hole in the diaphragm.
Generally a sticky float will flood into the engine when sitting, did she by chance leave the fuel on between first and second run? Can also disconnect engine breather from inlet manifold incase it's pulsing and pulling fuel.
Check all fuel vent hoses on carby to ensure they do not have mud dauber nest in them.
Also check air cleaner.
First guess pulse pump, second, needle/seat/float.
Good luck

 

[BruceP]

I have been workin on engines for over 30 years... gasoline in the oil is most often caused by the carburetor float-seat not sealing properly. If you run gasoline with ethanol in it, your carburetor will get pretty gummed up. It is best to look for NONethanol gasoline. (engine will run better too!!)

To a lesser extent.... overuse of the choke/enrichener can also lead to fuel in ihe oil. Only use the choke a minimal amount to get the engine started.

As mentioned by previous poster... always ALWAYS turn off the gas petcock when not running the engine. (Some rigs have an 'automatic' gas shutoff so there is no manual lever.) In this case, you need to look into fixing the automatic gas-shutoff.

If you are going to store ANY carbureted engine for more than a couple weeks, turn off the gas petcock and run the carburetor dry of fuel. In this way, there is no gasoline in the carburetor to leave residue when it evaporates.

 

[Daren Todd]

100 td, vents are clear on the carb. I had literally just cleaned the carb last week, and returned it to them last Tuesday. Unit sat till I moved it Saturday to put some wheel spacers on it with new rims and tires on the back. Doubled checked that the fuel was shut off before I tarped it.

There is a diaphragm in the top of the carb, but the line coming off doesn't attach to anything. Googled a diagram of the carb for that model, and the only line that hooked to anything was the fuel line. Then showed the crank case vent hooking to the air filter box.

When I was operating it, the thing was running down the road like a scalded dog would tack out and get up to 40mph in no time flat, and puttering around the yard, I could whip it into doing a donut or drift it around a corner easy.

As far as what my mother in law did, I couldn't tell you. I don`t know if she left the choke on. From what I've been told, she only ran it long enough to get it out of her yard and run a 10th of a mile down the road before it started spitting and sputtering on her. Then started freaking out because she saw fuel dripping. This in turn freaked out my father in law. I couldn't get any info from them except that it was leaking from the nut on the bottom of the carb.

When they showed me, they were pointing at the idle adjustment. I checked the oil and noticed it was over full. Then popped the seat and it had gas and oil blowing out of the crank case vent.

Its got me wondering now if the pepcock may not have sealed completely in the off position when I parked it.

 

[Redlands]

I learned the hard way that some fuel pumps will allow gas into the oil.

 

[W7AX]

I would probably rebuild that carb. They have a kit for that. Might be the needle seat is worn after this length of time. It's always a good thing to turn off the fuel when it's not being used. I have a couple of ATV's here and vowed I would never buy another carbureted unit. These are both fuel injected rigs. And as someone stated, always use non ethanol gas in an older rig like yours. Fuel pump diaprahms and carb seals do not fare will with ethanol on the older rigs. In fact a lot of them warn you NOT to use ethanol.

 

[Tooljunkie]

As mentioned,choke left on.
Unless you replaced the floats,needle and seat it could be dumping fuel.
It doesent take much fuel to flood a crankcase.
If carb is flooding,it should pour out overflow tube.

I believe that atv is gravity feed,so no fuel pump to leak fuel into crankcase.

 

[coachgeo]

I once borrowed a friends DATSUN 510 for a bout a month cause I was carless after an accident in mine. (have returned the favor five times over to other people in thanks). It ran like a scaled dog just like your description of the ATV... but I could always smell gas... decided to change the air filter... while pulling it.... the whole carburetor nearly came off.. no wonder I smelled gas... only thing holding on the carburetor was engine vacuum and throttle linkage.

Point is..... maybe in this case... how well it runs shouldn't be considered a factor in what the problem is or isn't?