Gas in the oil AGAIN! Help!

Working on this ‘80 XJ650 Maxim and I’m now going to need to swap the oil a third time. Cash down the drain again. Not to mention putting these carbs back on is a huge pain.

Vacuum petcock is good. I leave it on while it’s off the bike. Never dripped a single drop.

Originally the floats were too high. I adjusted all four down so they shut off much earlier

Float valve needle and everything seem great, no signs of wear whatsoever. I’ve hooked up and aux tank full of gas to see if the float needles would perform under pressure and I got zero leaks.

I just took the carbs off AGAIN and stuck the gas supply line in my mouth with the carb bowls off to feel/hear air coming out. I tipped the carb back while blowing and the air shut off the minute the floats rotated closed. I was actually surprised how hard it was to push any air past them if I really tried.

Ive read a lot of threads that mention potential issues with the fuel enrichment circuit. I have to full “choke” to get this thing to start. Once it’s running the plugs come out super white. That’s a separate issue as it seems the carb boots are cracked and we’ve got vacuum leak. But it’s not showing any signs of flooded cylinders. But I ran it around the block with fresh oil last week and not only did the oil smell like gas, the oil level went up above the window. We’re talking a 5-10 minute ride here.

So bothered right now. Just doesn’t seem like the usual suspects, they all seem to pass tests with flying colors.

 

Hi Mate, something not right here. I suggest doing a couple of tests. First have the fuel valve on reserve and check the floats are holding with the bike sitting. You can check this easily by connecting a clear tube to the float bowl base and opening the screw.

If it holds then you know the float level is correct and all 4 are holding. Then it must be excess fuel getting in when its running, but that doesnt make sense if your plugs are white. They should be very black if it was that bad and I doubt it would run without just fouling the plugs, certainly cant see how fuel would get to the sump while its running.

My bet is something is wrong with the float level or fuel valve and fuel is passing through when its not running and making its way to the sump. I've done a couple of carby build videos on my youtube channel, maybe check them out. My channel name is Mezzmo Engineering. Sounds like you need new carby boots too, once you do that getting them on and off is quite easy....

 

Just to clarify things, you didn't have gas in the oil and the oil level was good before you took the ride? While you were riding the bike for 5-10 mins is when the gas leaking into the oil?

You have checked to see if all spark plugs have spark? If you have a dead cylinder it would still be pulling gas into the cylinder, not burning it and the gas has to go some place. It would either get burned when it hit the crossover collector or find its way to the oil in the sump.

Was the oil supper dirty when you changed it? If you have gasses passing by the rings (low compression) gas and exhaust could find its way to the sump as well.

Give us a little more trouble shooting as to what you have done to this point. When I first started working the XJ bikes, I had to pull the carbs six times before I got them perfect. So now I really take the time to do the work right the first time. I am not saying you didn't, I am just saying I didn't and it took many times to get it right. Good luck.

 

Did you replace the float needles, or just reuse the old ones?

 

You’d have to have some seriously worn rings for that much gas to get through cylinders and into the oil that quick. I would thing it would run awful if that were the case.

Did you check your valve clearances? sync your carbs? is Your airbox loading up with fuel/oil?

 

Oil had just been changed and at the proper level. Rode once down the street and back to test and boom, gas in the oil.

Yeah all cylinders have spark

Oil was only a little dirtier than new. I will say that the oil got milky after the ride looking through the oil fill level window.

I tested the carbs again last night blowing into the fuel line and they really seemed to seal off well. No issues with the petcock. Those seem like the natural answers so I’m lost unless there’s some clever answer surrounding the fuel enrichment circuit or something since I’ve had to use that a lot with such a lean mixture due to leaky carb boots.

 

See both posts above.

 

Did You do any engine work in this? Did this just start happening? We need more background

 

i would guess a leaky petcock, not leaking through the normal way , to the "on" position , but leaking to the vacuum line, and into the carb boots, directly into the cylinders .
if that is the case, then all carbs will appear good (as they do).
clamp off the vacuum line at the petcock, and run the bike on prime, see how that goes
stu

 

Running it on PRI won’t make a difference if the vacuum line is clamped. How about:
-disconnect the vacuum line and see if it leaks at the PETCOCK vacuum port there.
——-make sure to cap the vacuum port on the intake boot
——-make sure to put the petcock on PRI or you won’t go very far

 

surely, running it on PRI, is the ONLY way it will run , if the vacuum line is clamped

 

Only IF the vacuum diaphram and the o-ring are working properly. WHen bth parts fail (and they can at the same time) fuel will bypass the valve and flow into the fuel line.

 

Exactly my point

 

Ok I really like the idea of the vacuum petcock leaking from the vacuum port. Never thought of that and it would definitely line up with what I'm seeing.

To answer some of the other questions, no I haven't done anything to the engine. It's a friend's bike and he just asked me to get it running well for him. I initially swapped the oil and rebuilt the carbs with new jets but not new float needles as they seemed to be in really good condition. Put everything back together and oil leaked in again. Took it all back off, checked the floats (shoulda done this the first time), they were quite a bit off. Adjusted and it seemed great. Tested the carbs with an aux tank and ran it till the fuel stopped going in. Waited for a minute to see if anything would leak and I got gas coming out but it was coming from the brass connector between carb 1 and 2. I swapped the o-rings and reassembled the rack. Tested again with aux tank. Now zero leaks anywhere. Changed the spark plugs (were jet black so the bike wouldn't really start) and oil again and took it for a ride. Threw it up on the center stand the next morning and the oil was above the top of the window. Now I'm super annoyed. Popped the fill cap and it smelled strong of gas. Pulled the plugs but they were bright white. I figured it was running super lean because I had to keep the fuel enrichment circuit fully open to get it to start cold and stay running. Just pulled everything apart again and there was gas going into the airbox and it seemed to be a puddle liquid gas also in the lip of the carb boots. I decided to take the carbs and blow into the fuel line while slowly turning the carbs over until the float needles engaged. Once they fell over it closed up tight. No leaking at all, confirming prior tests. So how we have gas everywhere but white plugs is beyond me. I also have no clue where the gas would be coming from if BOTH the petcock and float needles seem to be functioning as they should.

 

Well,
-gas can only come from one place: the tank
-It can only get into the oil four ways
1. Through the piston/cylinder rings
2. Through the crankcase vent tube
3. Through valve stem seals
4. Through a head gasket

1. cylinder rings - you’d have to have terribly worn, upside down, or missing rings to be dumping that much fuel into the crankcase.... or a hole in a piston. Either way you’d probably not be running well, if at all. In order to get fuel into the chamber it’s gotta go either through the carbs or the vacuum line. No other way possible. Compression test, leakdown test

2.crankcase vent tube - for this, you’d have to be dumping an awful lot of fuel through the carbs and backflowing out of the AIRBOX boots into the airbox AND have a clogged drain tube, filling up enough to get sucked in after the crankcase pressure drops.

3.valve stems seals - well if the seals are trashed I guess you could get gas blowing past them.... in which case your compression would be so bad you probably won’t be running well, if at all. Compression test, leakdown test

4. Head gasket - cyl pressure could blow excessive gas into the crankcase..... blowing polluted oil into the airbox. Compression test, leakdown test

BUT, those tests may be in-Accurate/ineffective if valve clearances are out of spec.

 

Just an update on this:

I’ve replaced the engine side carb boots to eliminate an air leak/lean condition. I checked the carbs and floats again again and everything seems fine. So I decided to try and drain a little oil so I can see the level again. Now it’s back to mid-window when cold. I left the petcock on PRI for 3 DAYS to be sure it wasn’t leaking. Airbox side boots are still disconnected. I also left the petcock vacuum line off to be sure. After that period the oil is still at the same level. I ran the bike once per day to get it moving to see if it could be forcing some through the seals or valves. Nothing changed.

So that seems to have eliminated the float needles as the culprit, no? But then it begs the question, where did the gas come from?

Tonight I ran the bike till it got warm with the petcock in the ON position and the vacuum line attached. First off, the bike ran great with the new boots. Second, I pulled the vacuum line and didn’t see any fuel in there in the event it was leaking via the vacuum line. I’ll check the oil level in the morning to see if anything changed there as well.

What would you do next?? There is evidence of gas in the airbox and the filter smells of gas. So it got into that area previously as well. Does that help guide me to another possible issue? I still can’t figure out how gas is getting from the tank and bypassing the float needles.

Sorry, this is very frustrating. Thanks for your help again.

 

At this point it seems like you had a float or float needle that hung up, and is now working correctly.
Hopefully the problem does not reoccur at this point. If it does then I'd recommend polishing the float needle seats, and replacing the float needles and the fiber washers for the seats (since you will have the carbs off, it's better to do all that at once instead of having to pull the carbs off again to do it should the leak not be fixed at that point). IF you need to do that make sure to order the needles from @chacal. There are kits on the market that have the wrong float needles included in them, so those are to be avoided.