Cleaning Bottom End With Gasoline

Moto Man26

Member
Aug 6, 2006
41
0
Hi all, I recently purchased a yz250 that needed a top end.... The guy I bought it from, told me he cleaned the bottom end with gasoline, and re-installed the top end and ran it with an old piston. When I took the cylinder and piston off, I spun the crank, and saw some drops of gas come up on the crankshaft.... Wouldn't this mean he never ran the engine, because there is drops of gas coming back up when I spin the crank? Because if he would of ran the engine, wouldn't the remainings of gas from the cleaning, burn up from the heat of a running engine? Or can it be from kicking the bike over just to check the compression, and it sucked gas into the cylinder and went between the ring and cylinder gap and fell into the bottom end? Also, is it ok to run an engine with some little remainings of gasoline in the bottom end from cleaning it? Any help will be appreciated!!!
 

IndyMX

Crash Test Dummy
~SPONSOR~
Jul 18, 2006
5,548
2
Amo, IN
When the pressure from the crank case draws the fuel/air mix from the carb, it doesn't go into the combustion chamber first. It goes into the bottom end, then is drawn up into the combustion chamber from the transfer ports.

This might account for the gas you see..
 

BigRedAF

Member
Jan 9, 2005
739
0
Something else is going on here?

Liquid gas doesn't just run into an engine. When the engine is cranked it draws air through the carb and draws out metered fuel through the jets. That fuel gets atomized into a vapor that gets further atomized as it makes it's way through the reeds and stuffs the cases. If you have lots of wet gas in the engine I would think your float level is set to high or your needle and seat has failed causing fuel to overflow into your engine.

As far as going between the ring gap goes that's all wrong...

When the piston is on the compression stroke it causes a vacuum that draws fuel in through the reeds. When the piston is on th exhaust stroke it pressurizes the cases closing the reeds and forces the fuel/air mixture up the transfer ports to arrive at the top of the piston so that the next compression stroke is full of fuel that's ready to be compressed and ignited. The rings just help to seal the mixture between the piston and head after the piston passes the transfer and exhaust ports on the way up.

Blow the fuel out of your cases with compressed air so that you aren't trying to start a flooded engine once you get it back together.

Good luck...
 

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