Hello All,

Just remembered a bike I had in NZ, that I never figured out before the bike got nicked.

Basically, I bought an '87 Yamaha 250 SRX dirt cheap sight unseen.

Soon realised why it was so cheap!

The tank was rooooooted - really rusted out from the inside - but a litre of epoxy resin eventually fixed that.

However, it did have an interesting problem where it would run ok for about 2 days, but would then just start spluttering/dying/not starting. When it did this I would have to do an oil change - and upon taking the sump plug off I would get about 2 litres of petrol along with the 1.5 litres (? from memory, may have been 750ml) of oil.

The only thing I came up with at the time was that the carbie must have been a bit rooted, and leaked petrol into the cylinder when it wasn't running - and that there must have been a crack in the cylinder head/cracked O ring/???? that was then letting the petrol down into the sump.

There was also a breather tube that was going from the gearbox to the airfilter - I guess petrol could have been flowing backwards as well? (ie, from the carbie into the air filter, and thence into the sump)

Any other ideas?

It's a totally moot point, seeing as the bike got nicked (and I got a lovely insurance payout ), but I'm just curious if anyone else has any ideas...

Sticky or worn needle valve, coupled with worn or left on petrol tap. This would allow the float bowl to overfill and the petrol runs down the inlet tract, past the valve head into the combustion chamber then down past the rings into the cases.

When tanks rust, the rust "dust" gets into the carb float needle valves which causes them to stick open. The carbs flood and the fuel runs into the cylinders and settles on top of the pistons and dribbles past the rings and into the sump, polluting the oil. Only way is to replace or line the tank, then strip and clean the carbs fully and if necessary replace the float valve neeles and seals. Took me ages to suss this out on my old Kawa 400!
Mike