Fuel in Crankcase and Airbox

I have an 82 XJ 550 and my problem is that I am getting fuel in the crankcase and it is also coming out of the airbox via the venting tube. I have replace the needle and seats in all carbs as well as rebuilt the petcock valve.
I get the fuel/oil mixture in the airbox when I rev the motor to about 6000 rpms and then let off. The fuel just shoots out of the airbox from the crankcase vent.
I have adjusted the floats and have ruled them out because I believe that fuel would backup in the carbs and not make it to the crankcase.

I think the problem is in the cylinders. Either a bad piston or bad rings. I dont understand how that much unburned fuel would make it into the crankcase.

Any help would be great.
Thanks
-Jeff

 

Please have a compression test done.

Fully charged battery.
Spark Plugs out.
Throttle wide open.

Post results at your earliest convenience.

Complete your "Signature section" with your bike "Thumbs"
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Year - Model - Mileage - Stock/Mods? (Fuel in CC-Oil)

 

Two things...
1. It's said that petcock rebuild kits only work less then 50% of the time. You can verify that the petcock rebuild is good by removing the fuel line at the petcock with the lever pointing to ON. (This is done with the bike NOT running.) No fuel should come out.
2. Often new float valves stick open. This is difficult to perceive unless the overflow actually comes out of the overflow joints between the carbs and pours onto the engine or ground.

Z

EDIT: Correction for grammar.

 

I had the same problem. I also had the petcock valve rebuilt. The fuel gets into the crankcase by leaking petcock and leaking needle & seat. This overfills the crankcase and at high RPM's the crankcase pressure blows the excess into the air box. In my case it caused the engine to stall and refused to restart until it sat for 1/2 hour to 1 hour. I saw the drip from the airbox and knew where to go from there. Strange thing is I haven't had a problem since that one event.

The fuel does backup in the carbs and runs out either into the airbox, or down the intake, thru an open valve, into the cylinder, and past the rings into the crankcase.

Bad piston or bad rings would create an engine that would be hard to start, run poorly, smoke, and foul plugs. As RickCoMatic says, do a compression test and you will know right away if that's an issue.

 

Today I fired up my bike for the first time in a few weeks, and I've having the same problem.

Only mine happens at idle. I did check the petcock and it's not leaking; and I wouldn't think the carbs are out of adjustment (had them cleaned/tuned last October, and the bike runs smooth).

 

If fuel is coming out of the overflow joints when you start the bike, especially after replacing the float needles and seats, try tapping lightly on the ends of the carb rack with a wooden handle to "encourage" the valves to seat properly.

I'm not sure there is a definitive fix for this except doing the above through an arbitrary "break-in" period for the new float valves.

Z

 

I did a compression test on all cylinders and they all where correct at 140-150psi

Any more suggestions???
-Jeff

 

I looked at the fuel petcock again and

On-no fuel
Res-fuel
prime- fuel

I put in a rebuild kit but could that not have fixed the problem or would I have to put in a new petcock all together??

I also did a test by stopping fuel to the carbs while it was running and even more fuel poured out?

-Jeff

 

Which Float Valve Pins came with the new set?

Solids, solid rubber-tipped ... or, rubber-tipped and lift-pin spring-loaded???

 

The needles were a solid with a rubber tip.
The seats are a solid brass I belive or some sort of steel.

-Jeff

 

What I don't understand about this problem is how on earth is all this fuel getting into the crankcase. I can't see how the fuel is getting by the pistons so fast and in such large amounts. Is there any other bypass that I am not seeing on this motor (82 XJ 550).
To me there is more fuel coming out of the airbox then could have in the all 4 carb bowls.

-Jeff

 

You really need to do a Compression Test and a Blow-by Test.

You need a Compression Test Gauge and a home made tool.

Knock-out the ceramic insert of a spark plug with a hammer and a pointed tool. Clean it out until there's nothing in the threaded base but the hole for the electrode to pass through.

Cut the air valve off a bicycle tube.
Trim-off the rubber at the bottom.
Chuck it in the drill and sand down the outside diameter of the bottom to fit in the spark slug base.
Stick a soda straw up into the inside diameter of the air valve.
Push the air valve and soda straw into the spark plug base.
Add epoxy to top and bottom around valve at top and soda straw at bottom
sealing the air valve tightly within the plug base.
When it cures ... you should be able to cut-off the soda straw at the bottom and have a tool to use to pump air into the cylinder.

Put each Piston at TDC and have someone pump air into the hole and see if it pumps-up or leaks.
You'll hear the leak.

 

RickCoMatic,
You, my friend, are the master.

Z

 

Very slick idea Rick!

Jim 8)

 

I am going to try it tonight. The compression test was about 145-155psi. To do this blowby test do I want to exceed the air pressure and if so by how much.
If I go say 200psi will that hurt anything in the engine?

Thanks Again
-Jeff

 

Rick, I'm nominating that as one of the top 10 homemade specialty tools of all time. Your creation or borrowed design?

 

Don't bother.

If you have 145+ psi ... it's not blowing by ... those are GOOD Numbers.

We have to figure out where the gas is getting in to the engine from.
There aren't too many places connected to a source of fuel.
4 Carbs.
One or more is dumping.

Now then ... seeing as how the bike will make 6000 rpm's ... and -- THEN flood-out when you close the throttles ... THIS makes me suspect that you have one or more of your Carbs FAILING ~~> "The Clunk Test" !!!

If the gas is still getting "Sucked-in" to the Cylinders after the engine has been run above 4,500 rpm ... The Carbs are feeding fuel through the MAIN JET.

For FUEL to continue entering the Combustion Chamber after the Throttle is closed ...

The Diaphragm Assembly(s) are NOT CLOSING -- or, -- are HANGING UP allowing the Fuel Supply from the MAIN JET(s) to continue to enter the Combustion Chamber(s).

You need to:
Check each of the Diaphragm Assemblies for "Stiction"
Your Carbs MUST ~~> PASS <~~ "THE CLUNK TEST" !

The Clunk Test:
(Here you go ... Make it happen!)

There have loads of Posts, recently, concerning performance and mixture settings. Generally speaking, the mixture settings of the carbs won't un-set themselves and cause your bike to start running poorly. Other factors, unrelated to Jets, floats, sync and pilot screw settings will. The Number-1 cause of a decline in performance -- "Related" -- to carburetors is "Slide Piston Stiction." The brass piston part of the diaphragm assembly needs to have 100% absolutely FREE travel in the carb body cylinder bore. No. A tiny bit of drag IS NOT OK. There needs to NO drag. NO friction. NO binding. NO 'Nuthin!!! When you get done CLEANING a set of carbs; you need to do "CLEAN-TUNING" too. You do this by conducting a "CLUNK TEST."
With the top off ... spring out ... and diaphragm un-seated to its locating channel -- LIFT the brass piston to the top of its travel and let it fall. It needs to FALL! It absolutely MUST drop ... from being raised-up and let-go ... like a safe out a second-story window! If it chatters down, hesitates, acts like it being hydraulically controlled, is slow, stops and goes ... or, does anything, other than drop ... like a wet bag of cement ... you got a performance problem. SLIDE PISTON STICTION. Get rid of it. It's easy enough to do.
Polish the brass piston. It should be a shining brass object a Marine Corp Recruit would be proud to show his Drill Instructor. You can polish the needle, too! BUT -- DON'T bend it!
The carb body bore is usually where the problem is. A film of oxidation forms on the Inside Diameter of the cylinder bore surfaces. This film reduces the inside diameter's already close tolerance to make the brass piston's travel become impaired. Elbow grease and finishing papers will restore the original shine to the alloy.
Use # - 800 Wet-'O-Dry to clean the surface. Vertical motion only. Refinish the bore with 800 using WD-40 as the wetting agent. Using sections of 800 about the size of a pack of matches ripped in half ... refinish the inside diameter of the bore. Throw-away the 800 section as it becomes fouled. Refinish UP and DOWN ... moving ALL AROUND. Don't do anyplace where you think its sticking. Keep the bore round.
Feel like doing another 15-minutes of work that will give you a stage closer to RACE-PREPPED??? OK ... after you clean-up the bore with the 800 Wet ... Hit the bores, AGAIN, with 1000 - 1200 and 1500 !! WD-40 is your wetting agent. When you are done, there should ZERO drag. Nothing preventing the diaphragm from raising the piston when vacuum is present. And, NOTHING from preventing that SPRING and NO VACUUM from allowing those slides to slam-shut for some ABSOLUTELY wonderfully controlled engine braking.
I know you! You're a sneaky little devil ! You ride like an accountant all the time, huh? Until the "Ride-Hard" bug bites you in the butt and you want to twist-again ... like you did last summer. We'll ... now you get to appreciate having sore fingers and elbows for a little while, doin'-up your carbs.
You'll be coming into a nice sweeper or a really sweet decreasing radius turn ... you tach-up for gear-change and the bike sounds like Formula-1 ... right-up to where you need to match RPM for the downshift -- immediately. No farting-around with the throttle -- "Asking Scotty for a few more revs. You're there ... on the hairy edge of sweetness. You matched your revs and now want to loose some speed ... close the throttle and you have On-The-Track engine braking. You're power goes back on without a hitch as you start looking like the guy in the commercials and sales brochures ... leaning over in the turn.
You exit the corner and wrist-open for the straight.
Hang on tight, brother ... you'll be going fast in a second!

 

Thanks again rick, I really appriciate all the time you have put into helping me with my problem.

I will work on it in the morning and give you an update.

Thanks Again, Jeff

 

We got to get that bike going; right.

Post where you are from ... under your Avatar.

You might be able to team-up with someone to get it running GREAT!

 

hello everyone,
I may have fixed the problem we will have to wait and see.
I do have to say that I wil get the dumbass award .
Last night I did what rick said and took off the top of the carbs and did a "clunk test" everything seemed fine and I did stretch out the springs for good measure. I ran it again and same problem, fuel in the airbox.

I did some pondering and took off the oil filler cap and it was full of liquid (oil and gas). Well I then took off the filter to drain it out. (here is my dumbass award) Not much came out, well I have done this before and just figured that maybe it was neer empty because it was all on the ground.
:idea: Hey dumbass, maybe there is drain plug (and yes I have used this in the past, but for whatever reason I forgot about it). I unscrewed the drain plug and it out came 1,2,3,4,5.......6 quarts of oil/gas. (this included the 4.5 quarts that I had added the past two times I took off the oil filter). :idea:

I then put on a new oil filter and poured in 2.6 quarts of oil. The bike ran perfectly. I took it out around the block.
However, I hope that fuel stays out of the crankcase. I do not know how it got in there maybe overtime or bad needle and seats or what all I know is that I will proudly display my dumbass award and hope that all the trouble I caused everyone will pay off in me not having to fix this again.


Thanks so much everyone for your imput. :lol:
-Jeff

 

ouch, i would have had a few of them quarts all over my floor. My pan i use will only hold a hair over 3 quarts.

Glad you got the bike running good again. Now go enjoy the long weekend.

Rob

 

I just purchased a 1981 XJ650 and have a similar problem. I also did the dumb thing of over filling the oil and the bike dumped out about 4.5 quarts when I changed the oil for the first time.

The oil was very dirty and smelled like gas. I filled it with 10W40 and added a bit of sea-foam to help clean out the crank case, idled it for a few minutes, and then dumped the oil and sea-foam. Then I filled it with more 10W40 to "rinse" it out, and dumped this as well (still pretty dirty looking). Finally I filled it with 20w50 and left a little room in the oil level viewing window. It seemed to run just fine and drove it about 10 miles and checked the oil level. There was only a small bubble at the top of the viewing window, and I also smelled the oil from the filler cap area...had a strong gas odor. So...gas is still getting into the oil.

I have no idea how long ago the carbs were cleaned, or if they are even the problem. It might be the petcock valve?

I'm taking the bike in this Saturday for a tune-up. Is there a quick way to figure what the source of the problem is? Or I should I let the mechanic at the Yamaha shop work on this? This if the first motorcycle I have owned and I know little of engine repair/troubleshooting. I'm more than willing to learn, but could use a little guidance on this.

 

Wendall79, welcome to XJBikes.com and congrats on your new purchase. A few things pertaining to this site. First, please use the signature portion of "My Account" to state your specific bike and year. Second, please start a new topic for any issues you encounter. Lastly, you may try the search feature of the forums to locate previous posts on issues that arise. These steps will help us help you.

The issue that you've mentioned is a common one for our aging bikes. Please see more info in the next two links and post back if you have any questions. We'd be glad to help.
http://www.xjbikes.com/Forums/viewtopic ... html#31525
http://www.xjbikes.com/Forums/viewtopic ... html#37882

The bottom line is that if you're getting fuel in the crankcase, your petcock and at least one float valve is bad.

Again, welcome, and let us know how it goes.
Z