Gas getting into the oil. Any ideas?

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Gas getting into the oil. Any ideas?

Postby zachmiller408 » Sat Jan 06, 2018 1:15 pm

Hello everyone!

I’m new to this site and to the YZF600R community but for the short few weeks and couple miles driven that I’ve had my Thundercat I have fallen in love. It’s much more fun than the Ninja 250 I started off with. Haha.

A little backstory: I bought the bike and found out it would really struggle to start in the mornings or anytime it was cold, really. The guy I bought it from said it has only gotten about 200 miles on it since the spring time so I knew it had been sitting for some time. Well with that info I removed the carbs to do a good and thorough carb cleaning. Everything seemed to go smoothly with no hiccups other than the struggle to get the 3mm Allen to make its way into the four carb clamps. That was the hardest part. I disassembled everything, cleaned with good carb cleaner, and blew through every hole I could find. Put everything back together and she fired up with choke first thing in the morning. I was thrilled! I took her for a little ride and everything was great and running smoothly. Great throttle response and no dead spots throughout the rev range. Well I went home and parked the bike for a few hours. Had the feeling to check the oil and come to find out the oil level has raised significantly and now smells like gas.

I figured I somehow got a stuck float or the float needle not seating well and that caused the excess fuel to drain down into my crankcase, but after taking the carbs off again I have verified all the floats aren’t stuck and the seats seal great. I’m in the process of adjusting my float height, but could a float height that’s too high really cause that much fuel to leak down into the crankcase? I just can’t wrap my mind around it.

I’m going to submerge all four of my floats in the next little bit just to make sure they actually float, but that’s the last thing I can think to check. Any ideas anyone? Or has anyone had this problem before? Thanks in advance and I’m grateful for all the effort people put into this site!!
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Re: Gas getting into the oil. Any ideas?

Postby Reserector » Mon Jan 08, 2018 2:24 pm

Chances are that the vacuum operated fuel petcock is not shutting off. True, if all four float needles were sealing, that wouldn't matter, but if the petcock was sealing, the needles wouldn't matter.

There is probably a rebuild kit for it.
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Re: Gas getting into the oil. Any ideas?

Postby vashtsdaytona » Mon Jan 08, 2018 9:32 pm

yes float heights matter and can dump fuel into cylinder which would run past rings. if it wasn't doing it before you got into carbs and it is now likely there.

but also

how many headlights do you have 2 or 1? it matters
I have a full engines worth of bolts and hardware. if you are missing somthing specialty hit me up I will share.

Goodbye Ashwin, stay safe on the otherside.

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Re: Gas getting into the oil. Any ideas?

Postby Pussycat » Wed Jan 10, 2018 3:03 pm

I had the same problem when I first got my 600 what it ended up being is the float Bowl valve seat o-ring once I replaced it on my woes went away
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Re: Gas getting into the oil. Any ideas?

Postby zachmiller408 » Fri Jan 12, 2018 1:53 am

vashtsdaytona wrote:yes float heights matter and can dump fuel into cylinder which would run past rings. if it wasn't doing it before you got into carbs and it is now likely there.

but also

how many headlights do you have 2 or 1? it matters


I have only one headlight. Also, I don’t think this problem was there when I bought the bike since the oil level was right on, but I was also really careful to not bend the float tangs either when I took them out to clean them making sure to lift straight out after removing the retaining screw. :dunno

I’m going to do the clear tube on the drain of each bowl as well to see if any float is heigher than another. My calipers say they’re all the same height but we will see. I’m going to replace the spark plugs and do a valve adjustment while I already have everything off the bike though. I will report back if I’m still getting gas in the oil in a week or so!
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Re: Gas getting into the oil. Any ideas?

Postby vashtsdaytona » Fri Jan 12, 2018 3:00 am

Being single head light you don't have a vacuum petcock, so we can rule that out.

But typically with this problem float bowls are to full for one reason or the other. So checking height is a good idea
I have a full engines worth of bolts and hardware. if you are missing somthing specialty hit me up I will share.

Goodbye Ashwin, stay safe on the otherside.

YOSHIMURA Club
member #1 President

My technical mentors; Bpro, 893cv.

A monkey can memorize facts, but ask one to rebuild a set of forks.....
-Bpro

"I know what I'm doing is right, I just did it wrong."

2nd Gear Rebuild Vids Here: http://www.youtube.com/user/vashtsdayto ... sults_main

Fork Rebuild: https://youtu.be/7sgxwyaRDO8

I have carb parts. viewtopic.php?f=23&t=67234


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