Oil in the carb, need help.

[JTRICK8806]

I have a 1995 XP. Before I bought it the original 720 motor had been replaced with a 587, and it has a Mikuni SBN carb on it. The ski seems to run fine at slow speeds but when you give it more gas it dies. I replaced fuel lines, cleaned the fuel filter, the compression is good, the spark plugs look good but are perhaps a little bit oily, and I cleaned the fuel selector valve. Still the same problem. So I opened the carb to make sure everything was clean and looking good. When I opened up the pump side I found quite a bit of oil in there. I'm not very experienced with two stroke engines, but I'm guessing that there shouldn't be oil in the fuel pump. I cleaned it out and put it back together, I haven't started it yet though.

Should there be oil there? Could this be the source of my problem? The ski is getting plenty of oil, as it makes a lot of smoke. I'm thinking I may need to adjust the oil flow. Any help will be greatly appreciated.

 

[JPX]

The oil may have gotten in there due to someone filling up the fuel tank with premix gas/oil. If you have the stock oil injection pump, then this premix is not necessary.

If the engine had been recently rebuilt, it is possible that a mild premix was used for engine break-in. But if this was a while ago or the original engine, then it is strange oil is in there at all.

If might not be oil - it could be varnishing fuel as the gasoline breaks down from long term storage with a stabilizer. Or just junk from the fuel hoses, especially if grey color hoses are still on there.

 

[JTRICK8806]

It isn't premixed, and the fuel is new. The engine has been rebuilt, but that was a while ago. The hoses are all new. I think oil is making its way through the pulse hose into the pump since all the oil was on that side of the diaphragm. Is that normal?

 

[JPX]

Not normal - sounds like an oil seal at the rotary valve or oil pump is giving out.

 

[JTRICK8806]

Not trying to say that you are incorrect, because I certainly don't know, but could you explain how either of those problems would allow oil to make its way into the fuel pump? I didn't notice any oil in other parts of the carb other than the fuel pump.

 

[derek]

the oil is traveling down the pulse line with the pulse itself. the air leaves. the gas evaporates. the oil remains. i wouldn't worry about oil on the pulse side of the pump diaphragm. now, you are getting a lot of smoke. this ski has been sitting? a long time? the center crank seals will slowly weep oil into the crankcase over time. if he isn't running right, you probably didn't run it long enough to burn off the excess oil. if smoke doesn't subside in a few minutes of running time, possibly up to a half hour at idle, then you need to worry. never buy a motor until you are sure you need one. you might want to pull rot valve cover off to chech the seal behind the valve and check RV timing. if back side of RV is super oily that seal could be problem, but i have never heard of one failing. 580 in 720 ski. you need to check the ignition timing. the 720 mpem feeds in too much advance. it can burn pistons in a 580. there are warnings on 720 mpems not to run on 580 motors. maks sure you don't have more than 22 degrees total-preferrably 20 or 21.

 

[JTRICK8806]

Good information, thank you. What should the rotary valve timing be set at?

That oil in the pump still worries me though. It seems like it wouldn't be able to operate if it is full of oil.

 

[MontanaXP]

Is your fuel getting discolored in the tank or in the carbs too? I fear i may be having the same problem as you. Let me know if you've come up with anything since the last post.