Petrol in my oil!

[red_phil]

Title says it all really.

So what can cause petrol to get into the oil sump?
This is on a GSX400, but the engine is VERY similar to the GS500
The bike is a project bike, and new to me, so I am uncertain as to it's state of repair.

I am guessing possible candidates are
1) faulty petcock always allowing fuel through?
2) faulty float bowl needles and/or seat?
3) damaged piston rings?
4) the previous owner just trying to mess with my head?

I am not sure if the petcock on the GSX400 is vacume actuated as it only has 2 positions as far as I can see. 'On' and 'Res'.

[Rema1000]

In my experience(s), it was: petcock on PRI, plus float needle not seating correctly.  You can see a bad float needle by checking float level with the "u-tube" method.  The float level will appear way too high.  If you tap the side of the float bowl with a screwdriver handle, then sometimes it will come down, as the float needle seats.

Oh, and change the oil.  When this has happened to me, I have changed oil, then ran the bike for a bit, then changed oil and filter.

[scratch]

When you change the oil, do not run or start the bike to warm up the oil, drain the oil first to get rid of the gas, otherwise you might suffer hydraulic lock and bend a rod. Also, see if gas keeps running out the oil drain hole. If it does, you'll know that somehow gas is still leaking past something.

[My Name Is Dave]

When you change the oil, do not run or start the bike to warm up the oil, drain the oil first to get rid of the gas, otherwise you might suffer hydraulic lock and bend a rod. Also, see if gas keeps running out the oil drain hole. If it does, you'll know that somehow gas is still leaking past something.

Pardon? I have always been told, ALWAYS, to have the engine warmed up when you change the oil, even it is said to do so in the factory and Haynes manuals. Unless you are talking about a different situation, but I have always warmed up the bike before changing the oil.

Am I missing something? Again? :dunno:

Dave  

[scratch]

Yes, as now he has gas in the oil - 1. The oil is now thinned with gas, the gas breaking down the oil, and displacing oil, so that the oil cannot lubricate as well. 2. The gas is now displacing more air in the crankcase, and even though the crankcase is vented, the may still be 'pockets' (cylinder skirts) where there will not be enough air to compress (you can compress air, not fluid).

[red_phil]

Well I just drained the sump.
I got 5 litres of thin brown oily petrol out and when I took the tank off,  it was empty.
A quick test at a safe distance told me that the oil was HIGHLY flamable    

So new oil and it ran from what was in the float bowls.
Current theory is knackered petcock and float needles.

Also the oil seals in a few places have gone. Loks like I'm gonna need to replace most rubber on the bike.

[Rema1000]

On my GS, when I opened the carbs, I found some black gunk inside the needle valve seats.  I soaked them and blew it out with canned air.  But I can tell that one of the needles has more spring in its tip than the other.

If you do need new float needles or seats, see Kerry's note on the PartsNMore kit:
http://gstwins.com/forum/viewtopic.php?p=170528#170528