2003 Yammy F8 With Gas in Oil

[Shermanator31660]

I have done many a search on various forums and this "problem" with gas in the oil seems to only be with motors that haven't been broken in properly. My F8 has 4065 hrs on it now and it has just started to belch gas into the oil in the past 30 or so hours. There is so much gas in the crankcase that the only thing that keeps it from filling up more is the dipstick! When I change the oil and then take the boat out, it takes about 2 hours and the crankcase is full of gas/oil. A local dealer told me the needle jet was stuck, checked that and its OK. I also checked the fuel pump to ascertain if there was a leak from it into the crankcase but as far as I can tell the rubber diaphragms look to be OK. The motor runs great first thing, little to no smoke, starts good, continues to idle fine until the gas gets so high that the motor then starts to idle fast/slow. Any help would be appreciated as I'm getting tired of changing oil every time I go fishing! Sherm

 

[99yam40]

Re: 2003 Yammy F8 With Gas in Oil

Thermostat may be stuck open never allowing motor to come up to proper temperature, is the only thing else I can think of.

 

[Shermanator31660]

Re: 2003 Yammy F8 With Gas in Oil

The strange thing is that it runs great, use the choke to start it cold and then once it "warms" up it runs fine. Where ever the gas is coming from its in big quantities, I don't think its getting past the rings and if it were through the carb I would think the motor would run crappy. Sherm

Thermostat may be stuck open never allowing motor to come up to proper temperature, is the only thing else I can think of.

 

[99yam40]

Re: 2003 Yammy F8 With Gas in Oil

Not sure on that small motor, but look for any port from carb to crankcase where it could be coming from. Some motors have a diaphragm on the prime start system, but you said this has a choke.

 

[1Crazymechanic]

Re: 2003 Yammy F8 With Gas in Oil

I would definitely perform a compression and cylinder leak-down test on engine when warm.This engine runs on a minute amt of fuel, you should definitely notice a performance issue if it is "flooding" through carbs.

 

[Shermanator31660]

Re: 2003 Yammy F8 With Gas in Oil

This motor does have a manual choke which I checked and is operating properly. I too figure that if the fuel was dumping through the carb that it would definitely make a rough running engine, if it ran at all. Is there any way of checking the fuel pump on these to see if the gas is bypassing the diaphragm and then straight into the crankcase? When I blow on the intake port the air passes through the outlet port. When I blow through the outlet port air does not pass anywhere, which I believe is a good thing or else it would be blowing by the diaphragm that is sealed to the crankcase. At this point I'm kinda at a loss which way to proceed, fuel pump kit? Sherm

 

[99yam40]

Re: 2003 Yammy F8 With Gas in Oil

unbolt pump from motor but keep hoses attached,
pump primer bulb up tight and see if fuel comes out of pulse port
if any comes out then there is a pin hole or tear in diaphragm

there are check valves inside pump that keep the fuel flowing only one way
diaphragm is what keeps fuel out of crankcase

 

[Shermanator31660]

Re: 2003 Yammy F8 With Gas in Oil

I'll give that a try today, thanks.....Sherm

unbolt pump from motor but keep hoses attached,
pump primer bulb up tight and see if fuel comes out of pulse port
if any comes out then there is a pin hole or tear in diaphragm

there are check valves inside pump that keep the fuel flowing only one way
diaphragm is what keeps fuel out of crankcase

 

[Shermanator31660]

Re: 2003 Yammy F8 With Gas in Oil

Well, I hooked up the gas line to the inlet port, closed off the outlet port (otherwise the gas would just go through the carb) and then pumped the primer bulb. While doing that I worked the little plunger thingy that operates the diaphragm and budda bing, gas was pouring out of the plunger end that sits inside the crankcase! I'm assuming the problem has been found, would make sense that gas was leaking through this area and once the crankcase cavity was full the pressure against the plunger would prevent any further gas from leaking in and possibly blowing the motor up! Thanks 99yam40 and crew! Sherm

 

[99yam40]

Re: 2003 Yammy F8 With Gas in Oil

Apparently I do not know very much about this small motor, because I did not know this fuel pump had a plunger that sits inside the crankcase.
all the carbs I have seen have floats that operate the needle that closes off the fuel into the carb when bowl if full .
So fuel would not go through the carb by pumping the primer bulb unless there was a problem with the needle and seat not shutting off the fuel properly.
But I did not know about the plunger so I could be wrong

I hope you did find the problem.

 

[Shermanator31660]

Re: 2003 Yammy F8 With Gas in Oil

I just thought I'd give an update to this topic. I installed the new fuel pump and the gas leak has stopped, go figure! It was almost as cheap to buy the entire pump as it was just the diaphragm so, for over 4000 hrs on it I guess it was worth it..........Sherm