gas in crankcase problem

[Steve]

float level measured with caliper per the service manual specs, ...

Might be set to the right number, but were they measured at the correct location?

Measuring the floats at the wrong location will raise the float level by several millimeters.

if the floats were allowing too much fuel, it would go out the overflow vents right?

Yes, they would do that, ... if your carbs had overflow vents.

There are no overflow vents on these carbs. If the fuel level is too high, gas will flow right down the carb throat, straight into the engine LONG before it gets to the level of the BOWL VENTS (they are not overflow vents). The bowl vents are there to provide an atmospheric reference for the venturis to work correctly.

.

[koolaid_kid]

The other thing I always do when I have the carbs off is test them on the bench first. I connect my fuel cell and check to make sure the needle and seats are not sticking. If one leaks, I remove the fuel bowl on the offending carb and recheck/clean the needle and seat. Repeat until none leak, then I install the carb bank.

[BassCliff]

Greetings and Salutations!!

Hi Mr. Mharal,

This is the common wisdom concerning gas in the crankcase: Overflowing Carbs. Here are some pictures depicting float height measurments: Float Height Illustrations. You'll find quite a bit of general knowledge about these old bikes on that website. Now let me give you the S.W.A.G. for a new member.

If you are here you probably have a 30 year old motorcycle that needs about 20 years worth of maintenance. You'll find all kinds of helpful tips, procedures, manuals, etc, in the links below. Let's get started.

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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...



Please Click Here For Your Mega-Welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[tom203]

Mharal said....

",, but if the tank is removed there is no leakage from the gas tank."

That's a good sign!

Plus

"if the floats were allowing too much fuel, it would go out the overflow vents right?"

No, overflow if high enough rolls out engine side of carb throat and washes down cylinder towards crankcase,i.e., your problem. Sounds like one (or more ) of your float needle seats are leaking badly for this much fuel to get into crankcase so quickly.
With tank off, find some clear vinyl tubing that fits snugly over fuel line; rig up a funnel and pour gas in it- my guess is the fuel will quickly drop and head to leaky carb(s). Finding that carb is challenging with airbox on.

[Mharal]

thanks for that tip,, I will try that tomorrow and see what happens. the thing that bugs me is I recently rebuilt the carbs and replaced all the float needles and o-rings,, but will do what i need to do to get it going

thanks
Mark

[tom203]

That much fuel finding its way to crankcase so quickly seems to indicate that those new needles and seats are leaking. Probably best to follow koolaid kid's advice and remove carb rack and determine where/why the fuel is flowing.

[Nessism]

Just to reiterate: there is NO WAY for fuel to enter the crankcase with the engine running, even if the petcock has failed, or the floatbowls are overflowing. In those instances the fuel will flow into the combustion chamber and kill the engine. Now if there is fuel entering the crankcase after parking the bike, that's another matter.

Also, it's normal for the crankcase and oil to smell of fuel. Blow by gases mix with the oil and create that smell even if there is no raw gas in the oil.

A clear tube on the petcock vacuum line will help you determine if fuel is back flowing into your carbs. Be aware though, some condensation in the clear tube is normal and nothing to be concern about.

Measuring fuel level, not just the float level, is the way to determine if the carbs are overflowing due to leaking float needles. Sometimes when the float needle spring is weak the fuel level will be high. Also, with aftermarket float needles and/or seats, the float level will likely change relative to the original Mikuni parts. One more reason aftermarket carb parts are a pain in the arss.

Good luck and hope you figure it out.

[tom203]

"Just to reiterate: there is NO WAY for fuel to enter the crankcase with the engine running, even if the petcock has failed, or the floatbowls are overflowing. In those instances the fuel will flow into the combustion chamber and kill the engine"

Well,yeah, you'd think so, but what about just one carb overflowing and washing down its cylinder wall into crankcase- unfamiliar with bike , he might not notice it's running on 3 cylinders.

[BassCliff]

Hi,

thanks for that tip,, I will try that tomorrow and see what happens. the thing that bugs me is I recently rebuilt the carbs and replaced all the float needles and o-rings,, but will do what i need to do to get it going

Did you use OEM parts or a "carb rebuild kit"? Most aftermarket carb rebuild kits contain inferior parts that just don't work right. Something to think about.

Have a look at the links below (PDF files) for the proper cleaning/rebuilding procedures. Order O-ring sets from http://cycleorings.com.

Mikuni BS(CV) Carburetor Rebuild Tutorial
(Mr. Nessism)

CV Carburetor Rebuild Guide
(Courtesy of GSR and John Bloemer)
(Click here to see the CV Carb Notes)



Thank you for your indulgence,

BassCliff

[Mharal]

Just some background on the carb overhaul,, I installed the o-ring set from Mr. Barr,, float needles, small rubber plugs and bowl gaskets from Z1 all installed after carbs were dipped. i used the original for all other parts as they looked okay and were cleaned.


just an update,, I installed a new petcock just to eliminate that issue for good. I have verified that it is working properly.

next step is to pull the carb rack off and test fuel flow and cutoff and make any adjustments.

thanks for all the help and will let you know what I find.

[Mharal]

another update,, pulled the carbs off,, setup the tank, first I applied vaccuum and using a clear line for vacuum and gas,, I saw gas flow to the carbs and did not have any gas leaking anywhere. so then I cked the gas level in the bowls by attaching a clear line to the bowl drain and applying vaccum and then cking the level in the clear line ,, all the fuel levels in all bowls were good.

I kept vacuum applied and did not have any leaks at all,, so this tells me the float needles are stopping fuel flow as they should.

I am concerned that I did not see fuel coming out one of the carbs... not sure if the issue is fixed or not.

I am going to pull the bowls off and verify fuel is flowing and then stops by manually moving the floats,, but i would think I would have seen a leak if that was not happening.

Am I missing something? I would hate to put everything back together and see gas in the oil again.

thanks Mark

[BassCliff]

Hi,

Sounds like you're pretty much there.

I am concerned that I did not see fuel coming out one of the carbs... not sure if the issue is fixed or not.

I don't quite understand this. Do you mean that there was no fuel in the level testing tube? No fuel in the bowl?

"...coming out one of the carbs..." where?


Thank you for your indulgence,

BassCliff

[Mharal]

I was just hoping that I would see an obvious problem that I could fix,, like flow flowing from a carb that had a stuck float needle or something,, but did not see one.

[Mharal]

another update,, with the gas tank hooked up, pulled the bowls,, made sure gas would flow and stop by moving the floats up and down, that looked good, also verified the fuel level in the bowls was correct using the plastic tupes to verify the gas level---good and ,, then applied vacuum and did not seeing any leaks with everything hooked up--good

put everything back together,,, changed the oil,, verified oil level was halfway between the f and L levels via the sight glass,, went to get some more oil,, cause i ran out. came back and oil level was the same.

started the bike,, for a minute,, turned off,, cked the oil and needed to add some-- filled it up to halfway between the F and L sightglass.

Started the bike again and let it warm up,,, ran good,,, turned it off,, I have a clear motorcycle fuel filter and could see a air bubble at the top of the filter,, let the bike just sit for about 10 minutes,,, oil level was rising,, air bubble getting larger in fuel filter. cked the oil level,, Oil was past the F mark.

Somehow the fuel is draining out the fuel line below the petcock after the bike is turned off and only does it after the bike has been running.

I verified the floats were working properly and did not see any leaks with the gas tank hooked up and vacuum applied,, or not applied when i had the carbs off.

Looking for suggestions at this point,, I am not sure what to ck next.
very frustrating,, but i am getting better pulling the carbs.

thanks
Mark

[Nessism]

Mark,

Did you try a clear line on the vacuum hose to make sure fuel isn't flowing backwards down the vacuum line and into the #2 carb?

Just in case you haven't already tried this...

Find a flat piece of pavement and put the bike on the center stand. With a cold engine, take note of where the oil level is in the sight glass. Make sure it's between the marks, but not over. Drain or add some oil as needed. Then try running the bike for about 2 mins. before shutting down. Wait another couple mins and take note of any difference between your cold reading level. I suspect the second check level will be lower than the first but it should be close.

Now take the bike out for a good ride, long enough to get the oil up to temperature, and when finished, park on the same exact spot and put the bike on the center stand. The oil level will most likely be above the previous marks. Let the engine fully cool off (wait several hours) then check the oil level again. If it's above where it was previously with a cold engine, you have a problem.

Key thing to know is that oil expands when it gets hot. You need to check in the same physical location because if the pavement isn't flat, you won't get a good reading. Also, make sure the oil is cold, full cold.

Good luck and hope this helps.