Fuel/Oil Gushing..

[rgouette]

Ok, I have the feeling others have seen or heard of this.

Bike: 1981 Yamaha Maxim 650; 16K miles
Problem: some sort of feul/oil mixture is shooting out from the Crankcase 'breather?' tube that runs up to the air cleaner box.

Bike history: This bike was given to me recently, with the report that it had "leaked feul all over the ground" so it sat for the past 2-3 years.
I just put a battery in it yesterday, and it did fire up, but after about 4 seconds, this huge amount of feul/oil gushed out from that tube.

So, it seems feul is getting into the crankcase: but how?
Theories so far:
1) The previous owner lefthe petcock on 'Pri' and filled up the carbs, and now the crankcase needs emtying.
2) There is a either a bad/stuck float or non-firing piston


Any thoughts lads?
Cheers!
Rich

[poppygene]

Hey, Rich! Welcome aboard!

I'm gonna go with theory #2, sort of. My guess is that one or more of the float valves is leaking, causing the gas to overflow into the crankcase. This happens often with bikes that are allowed to sit for long periods with gas in the carbs and tank. A thorough fuel system cleaning is what it needs. I'd say go ahead and buy four carb rebuild kits for it - may as well, since you'll have to disassemble the carbs to clean the gum and varnish out, which is really the best thing for it at this point.

I wouldn't try to run it again 'til you get the carbs to quit leaking, the fuel drained out of the crankcase and put fresh oil in.

Good luck, and keep us posted!

[rgouette]

excellent, thx!
Rich

[kar_the_terrible]

normally your carbs wont get completely clean with just carb cleaner and compressed air. I used a bit of carb cleaner to get rid of the big gunk deposits.... and then 'cooked' the carbs it in a vinegar and water solution (remember to use plain clear vinegar) for about 40 minutes. it really cleans things up. Alternatively, of course you could just use dip.

If you go with the vinegar, after removing the carbs dont let them just sit and dry... flush out the idle circuit and the jets with a compressed air can and then let them dry completely. If you just let them sit, some sediment that wasnt completely dissolved away can still remain behind.

[TechTMW]

Before spending money on a carb kit, have the compression checked on all cylinders. Sometimes a problem like this indicates mechanical failure, so dumping cash into it right off the bat may not be a good idea.

[rgouette]

So, I pulled the carbs last night, but not before I uncorked the crankcase drain plug, & watch my EIGHT QUART bucket fill up!!!!
Man, that's gotta do something bad...

Guess I had a combination of full c/case, & sticky carb parts!

Rich
http://www.gouette.com/yamaha/yamaha.htm

[Gummiente]

Guess I had a combination of full c/case, & sticky carb parts!

Keep in mind that the gas had to drain past the piston rings first before collecting in the crankcase - this means that the cylinder walls have long been washed clean of any lubricating oil. I'd suggest you squirt a couple shots of engine oil into each cylinder through the spark plug holes, then crank the engine over with the kill switch off (if your bike is setup to do this, you might have to leave the plug wires off if not) for a few cycles before firing it up.

[poppygene]

I uncorked the crankcase drain plug, & watch my EIGHT QUART bucket fill up!!!!
Man, that's gotta do something bad...

Not necessarily. Lots of bike motors have survived a gasoline flushing!

That's a good pointer from Gummiente. I'd go ahead and squirt the oil in now and let it seep around the rings for a day or two. Couldn't hurt.

Once you get it running, I'd give it another oil change fairly soon to get the remaining gas out of the crankcase.

[Aggroton]

this is so funny the same thing happened to me on my 550...we discovered my friend who was the previous owner mistook prim for off...and my bike vomited out the air box. we flushed the oil and gas out with more oil and everything works fine now.

[rgouette]

Outstanding all, thanks!!!!!!