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gas in crankcase problem

  • Thread starter Thread starter Mharal
  • Start date Start date
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.
 
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.
 
"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.
 
Hi,

Mharal said:
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
Click to expand...

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
 
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.
 
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
 
Hi,

Sounds like you're pretty much there.

Mharal said:
I am concerned that I did not see fuel coming out one of the carbs... not sure if the issue is fixed or not.
Click to expand...

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
 
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.
 
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
 
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.
 
thanks for the reply,,

I am using a clear vacuum tube, so I can verify gas is not running through the vaccum line.

I will pull some oil out and ck it again using your process. I am pretty sure I have gone throught this process, but will not hurt to ck it again.

thx
Mark
 
Mharal said....
"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."

Only check oil when bike has been off awhile-checking after a one minute run will leave lots of oil in the attic giving a false level. After a run, my 650 takes a good half hour for oil to drain back.

New petcock, carbs floats bench checked OK- there's nothing else to fill crankcase so quick except you!
 
yep, understand,, I had changed the oil and the oil filter,, filled up the oil between F and L,, then started the bike and let it run for a minute or two to circulate the oil. turned off and cked the oil after it sat for while,, I did not wait 30 minutes,, more like 15,, then cking at this point the oil level was low because it circulated throughout the engine. i then added to get the level between F and L,, and then started it and let it warm up,, turned it off,, let it sit and the oil level appeared to stabilize at the same level,, but then it starts creeping up,, to past the F level and all you see if oil and thats when i noticed the air bubble in the fuel filter getting larger. I think the gas in the fuel line below the petcock is somehow getting past the floats and into the crankcase.

I am going to remove some oil from the crankcase,, ck the level,, it should not be changing at this point. put on a clear fuel line,, start the bike and let it warm up,, turn it off and then let it sit,, I would expect the oil level to be low at first,, then gradually fill to the originally level,, then I will watch the fuel line and see if the fuel drains down through the carbs,, if it does,, then the oil level will rise also.

if the above does happen,, that would mean the float needles are not shutting completly right? Just not sure why it would work on the bench and not on the bike.
 
I'm not understanding why you start with oil level between F and L, run it briefly and then add some more oil before it has drained back down. I run my bike all the time with cold level at 3/4 full mark- I don't fret that running oil level is below L mark- I think/hope that that's what suzuki wanted.
Your bench test proves that carb float seats are sealing well enough- and your new petcock is working.

Get cold oil level correct ,start bike, run briefly then disconnect clear fuel line at tank and observe. Oil will eventually come back to your original level - be patient.
 
Wanted to update what i have done. So I drained oil out of the bike until level was between full and low. Stone cold,, level was between f and L,, cranked it up,, went for a 20 minute ride, bike ran fine,, parked at same location, put bike on center stand,, i always do that,, disconnect the gas line below the petcock ,, could see gas in the line, , cked the oil level,,completely full,, let it sit over night,, oil completly full still and gas still in the clear gas line???

So i have completly drained all the oil out which smelled of gas,, gas line connected,, could see fuel in the clear fuel line to the carbs. I am going to ck the oil in the morning and see if there is any gas in the crankcase,, I suspect that there will not be.

it seems that gas is getting into the crankcase while riding the bike. Open for suggestions,, next step would be to pull the carbs again and go through them again. Could i have problem with the mid or high range jets? I really do not have a clue at this point only that it points to the carbs. could I have a cylinder not firing while riding? and would that cause the problem,, all pipes are hot and the bike does not hesitate or miss,, runs strong to me.

Need a plan of action,,

thanks
Mark
 
That part about oil level rising after 20 minute ride and yet you saying "the bike ran fine" does not compute. That much gas sneaking into crankcase during run, would cause the bike to run pitifully. My failed petcock fouled out #2 plug, causing idle drop, noticeable missing,and exhaust popping. I don't see how even oversized main jets would create this problem without the bike running poorly and passing gas into exhaust.
 
I believe the problem is the way you are checking the oil level. Gas can not leak into the crankcase while the engine is running.

Sorry for the struggle.
 
I hope you are right,, I drained the oil competely yesterday so there was no oil in the crankcase,, sight glass clear, no oil in the system at all. Then I hooked up the vacuum and gas lines and let it sit like that over night.


this morning I cked the sight glass,, still empty, there is no visible fluid in the sight glass, which is expected if the petcock and floats are working properly.

So that would confirm the petcock and the floats are working fine.

I will add oil,, 3.4 is listed as capacity with an oil filter change, also I am using Rotella T 15w-40 oil.

Going to add 3 qts and see where the level ends up in the sight glass.

thx for your patience.
 
The shaft drive 650 uses engine oil to lubricate the secondary reduction gears (shaft drive), and there is a cubby hole inside the engine which has it's own drain plug. I'm not sure how oil flows though the system but it's possible oil is accumulating somehow in various pockets inside the engine and draining back into the crankcase slower than one would expect.

The factory specified oil checking method involves starting a cold engine, running it for a few mins., shutting down the engine followed by waiting ONE min., then check the oil. The idea is for the oil to be cold, so it's not expanded. Run the engine so all the nooks and pockets inside the engine are filled up. Then let the oil drain back somewhat (but not fully). When you check this way the oil level will be lower than if you just let the engine sit over night.

When you first fill the engine with oil it tends to pocket in the clutch cavity so the level may seem higher than actual.

I mention all this to make you aware that you must take into account all the variables when judging oil level. Target the middle of the sight glass so it's easy to see the level. There have been lots of people around here over the years that think their oil level is too high/low, when in truth their was either no oil showing in the sight glass, or it was overfilled.

Good luck and hope you get it sorted.
 
okay,, I added 3 qts, ran the bike for a few minutes, turned it off and waited ~ 1 minute,, oil level was slightly below the L mark. I had to step away for a few hours and when i came back and cked it the level is halfway between the F and L mark. I think that is good. Going to try it there,, will ride it for while and ck it later and let you know

thx
Mark
 
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