1986 vf500 gas in my oil...lots of it

Finally rode the bike for the first time. Changed the oil for second time and iol ran out as thin as water. It smelled of gas. I cleaned and reassembled the petcock and ran the vacumme test on it with a mity mite. Only flows if the vaccume is applied. Turning petcock to off and no gas flow.
BUT Turning the petcock to off , the bike still runs for 5 +minutes. I finally pinched the main tank hose and then ran it and the bike STILL RUNS!
how long should it run to burn off the gas in all carb bowls? Anyone had this experience?

 

It shouldn't run for more than a minute or two, sounds like you might need a new petcock and possible float valve needle problems.

 

It sounds like the issue is with the float needles and float valve seats. Did you inspect these when you cleaned the carburetors? These parts can be reused, if they do not have signs of wear, though it is often best to replace these as a complete set - depending in part on the maintenance history and age of the carburetors.

Regarding the petcock, with the fuel selector in the OFF position, when you manually apply a vacuum to the diaphragm no fuel should flow - this checks out right? If so, from your description, the petcock appears to be functioning correctly.

 

YOU are victim of 2 flaws and one bad circumstance.

Flaw 1 is leaky petcock, which should kill the motor within about 1 minute in the OFF position.

Next is a leaky float needle.

Then your engine stopped where the leaky petcock, leaky needle and and an open valve conspired to flood the crankcase.

Do not run the engine until oil is changed and problems are fixed.

Have you considered a newer bike ??

 

I checked the float valve seats and could not find any grooves or flaws. Ill check the petcock for leaking.

I have changed the oil and clamped off the main fuel hose just in case.

Ill checK both again.

 

Gas in oil problem and fix...hope this helps someone else too.

The first thing did I checked the petcock on "OFF" position. Clear hose allowed me see a good sized trickle of gas. So it was loading up the carbs at rest, with or without vacumme. Explains why the bike would not cut off when I closed the petcock.
I ground off the rivets, disassembled the unit and found the large black rubber gasket had tears and wear between the feed holes. I pryed the gasket up carefully, flipped it over and the reverse side was like new. Installed it with a litte dab of form a gasket, and silicone greased everthing. Problem solved.

Thanks to all of the guys who responded and hope this helps other riders.

 

Gas in oil problem and fix...hope this helps someone else too.

The first thing did I checked the petcock on "OFF" position. Clear hose allowed me see a good sized trickle of gas. So it was loading up the carbs at rest, with or without vacumme. Explains why the bike would not cut off when I closed the petcock.
I ground off the rivets, disassembled the unit and found the large black rubber gasket had tears and wear between the feed holes. I pryed the 4 hole gasket up carefully, flipped it over and the reverse side was like new. Cleaned the unit, installed it with a litte dab of form a gasket, and silicone greased everthing. Problem solved.

Thanks to all of the guys who responded and hope this helps other riders.

 

he is so happy he posted about it twice........ cool , glad it worked ...but you should try to find that rubber gasket and replace it with a new one...I know ..needle in a haystack....

 

It only explains half of the gas in the oil problem. It shouldn't have got past the carbs unless the floats are messed up, no?

 

I was happy to finally get it solved and not have to pull the carbs again. i may have to fabricate a new gasket from scratch. bike runs great and is a blast to ride compared to my BMW r90s german monster.

 

BMW r90s german monster. Nice bike!!

 

+1

Good news on diagnosing the faulty petcock but,,,for piece of mind the float valves should be inspected - fuel got by one or several of these and flooded the crankcase through an open valve, as posted above.

 

You are right and it is hard to say since so far on the "OFF" setting no gas in the crankcase . I ran it on off as a test, and it shuts off from starvation in about 1.5 minutes. I turn it off , leave it overnight and smell the dipstick and no gas smell.
I think that steady trickle of gas loaded up the bowls and somewhere it flowed into the crank over time, or as my mechanic friend pointed out the gas build pressure and can flow right around the rings ...so i am watching things.
I am not leaving the petcock in the on position at all unless riding the bike as usual SOP. I do not trust the vacumme design or diaphram on this bike and it is no problem to switch to off since my other two bikes have manual petcocks that HAVE to be shut down. Otherwise they overload Mikuni's, the tank pressure overlads the needles, and my wife thinks the garage will blow up (she's right).
If I have a leaky float valve it will make itself known next oill change. I am going to leave it in the On position for a week as a test and then drain the oil and do the smell test.
The bike runs and idles great through all of the powerbands right now and I am riding as much as possible before the snow flys.

 

Glad the bike is running well. I certainly understand wanting to eke out the last bit of the riding season (esp. as I am on the East Coast).

This said, I would give some thought to carefully inspecting and possibly replacing the float valves over the winter - having any amount of petrol in the motor oil, esp. on a VF500F engine, doesn't sound prudent.

 

I don't know if I mentioned previously, but I know of two 500's in my area that bent their connecting rods in the last few years due to this gas in the crankcase problem . That's a lot of work to fix, so be careful.

 

Two issues, right?

1. gas can enter the crankcase via an open valve compromising the motor oil
2. gas can enter the cylinder, sit there, and then cause 'hydrolock' on the compression stroke - never a good thing

 

I believe #2 was the cause in both cases.

 

Makes sense.

 

This happened on my buddy's Chevy pickup many years ago, float leaked, crankcase filled with gas, buddy started the engine, blew the oil pan off.

 

Some nasty fotos of hydrolock @ Hydrolock - Wikipedia, the free encyclopedia. I've heard of this before, but never seen the results. Wow. That's some kinda force to bend rods like that...