Cb360 fuel in the oil?

Sderbyshire

Sderbyshire

Into Sailing, classic Triumph cars and motorbikes.
Hi guys

I think my cb360 is getting a little fuel in its oil

The bike was off the road for a decade, and the po bought some used ' refurbished carbs from somewhere.....

I cleaned them out and the bike runs well, but I think the oil level has gone up a little and the oil smells slightly of fuel.

I'm no carb expert......so looking for advice.

How does fuel get into the oil, is it a leaking float valve ?
How can I diagnose the problem?

Thanks in advance for your guidance

Steve
 
Floats may be too high (way too rich, extra gas washing down the cylinder walls while running) or they're sunk because they're full of fuel, the float needles maybe not be sealing letting gas dribble down through when the bike is shut off, or maybe the petcock isn't shutting the fuel off properly and it's letting gas continue to flow while the bike is sitting. Or it's a combination of a couple of those things. In any case, you're going to smell a bit like gas while you figure it out. :)

If your plugs are black, it could be rich enough for extra gas to wash down. Otherwise you can check the petcock by pulling a fuel line and watching to see if it flows into a bowl or bottle while the valve is shut off. Checking needles and floats means pulling the carbs off.
 
"cleaned them out" Did you break them down entirely and clean them, set the floats, bench sync the slides and then verify the seats were shutting off ?

I doubt the fuel is bypassing the rings while riding, but if the fuel is weeping into the cylinders it could be draining into the pan, I would individually open the bowl drains and see if the fuel just flows free with the petcock closed to verify that and then check to see if the floats are set right by holding the drain tube next to the carb and see how high the fuel is in the tube with the petcock open and the drain screw open, should be just below the gasket.

I would always turn the fuel off on any older bike at least every night.
 

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Thanks for the replies guys.

I cleaned out the carbs quite thoroughly, but I did not check the float valves were sealing and only checked the float height was reasonable.

I like the idea for checking for a leaky peacock and the fuel level idea, I'll try that with a transparent drain line.

Any ideas for checking for a leaky float valve?

I'm thinking of connecting the carbs to fuel off the bike and see if they leak.

I do turn the petcock off and I'm 90% confident it does shut off, as I cleaned it out and tested it when I cleaned the tank a month ago.

Steve
 
If your float valves aren't working, you would most likely be getting overflow through the brass tube on the carbs shortly after the fuel is turned on.

Introducing fuel to the carbs while on the bench is a good idea to rule out your floats as the issue.

Have you recently set your cam chain, valves, timing and vacuum synced your carbs while the bike is running? If the combustion sequence is off timing, ive experienced a bit of fuel in the oil.

Check the carbs, make sure everything is set up properly, then change the oil and run it for a bit and I'll bet you'll be good to go.
 
Getting back to this after a distraction fixing the rear wheel bearings......

The oil level does not go up with the bike standing and the petcock shut, it does go up on a test run.

So I'm thinking one or both of the float valves?

However there is nothing coming out of the overflows.

Guess I need to take the carbs off to investigate.

Was going to buy two new valves and try that, but genuine ones are quite pricey.

I've read that aftermarket jets are to be avoided, is this true for float valves as well?

Steve
 
Every time i disassemble and go through old mikunis they leak in the float valves when i plug it back in. Sometimes its enough to tap them with a screwdriver, other times ive had togo for a ride with the taps partially shut just to keep it running. Vibes usually cure it. But since your bike runs fine i doubt thats it. Usually pours out of the carbs as well.
 
Thanks David

So any thoughts on whether I need genuine Honda replacement float valves or are the aftermarket ones ok?

Steve
 
Sderbyshire said:
Thanks David

So any thoughts on whether I need genuine Honda replacement float valves or are the aftermarket ones ok?

Steve
Click to expand...

What do the tips look like? I absolutely HATE aftermarket float needles. They are damn near never to spec. If the tips aren't gouged or have a deep ring in them, you'll be OK. My favorite trick is using brasso and a q-tip. Polish out the float valve with the q-tip, until it's clean looking. Don't use a drill as you can take away too much material. Then do the same with the tip. Take brasso, put it on a paper towel, rub the tip in it and spin it if you can. That should help with any excess gunk that might be on them etc. Lastly, I don't know if it was mentioned...but do the tails of your float needles all spring in and out as they should? If one is stuck out or in, you will have a bad time :)
 

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Sderbyshire said:
The oil level does not go up with the bike standing and the petcock shut, it does go up on a test run.

So I'm thinking one or both of the float valves?

However there is nothing coming out of the overflows.

Guess I need to take the carbs off to investigate.

Was going to buy two new valves and try that, but genuine ones are quite pricey.

I've read that aftermarket jets are to be avoided, is this true for float valves as well?
Click to expand...

If the float valves are leaking, you should see fuel out the overflow pipes with the bike sitting and not running with the petcock open. As a rule, the carbs should be able to empty the tank via the overflows and not introduce any fuel into the throttle bores, so none should get into the engine and the crankcase. If gasoline is indeed getting into the oil, suspect a problem with the overflow tubes. And instantly change the oil if you even remotely suspect any fuel has contaminated it - or you likely will have far greater problems than the carburetors. It takes very little gas to pretty much destroy the lubricating qualities of the oil, and severe damage is likely very quickly.

Yes, OEM carb parts ONLY! But I find it very rare that I need to actually replace a needle and seat assembly. Clean them like MBB suggests. Any fine polishing compound should work great - even toothpaste! (If you don't have any Brasso laying around!)

Put your carbs together on the bench without the needle and seat assemblies and supply them with fuel. Fuel should fill the bowls and pour out the overflow pipes. You should not see any fuel in the main bore because it should never get high enough reach it - it should only get as high as the top of the overflow pipe. Be sure that the bowl vents are not obstructed, otherwise it could be possible that even when the fuel gets higher than the overflow pipe, it can't get out fast enough because of the sealed chamber. There should be a hole in the top of the bowl in the main casting and it should lead to a port on the side directly to the atmosphere. You can see two vent holes in MBB's picture. Blow compressed air into the hole and it should exit the port with almost no restriction. If all seems well, put the carbs back together and bench check them by supplying them with fuel. Do this from an overhead supply with a hose so you mimic the actual line and tank. The vertical distance from the top of the fuel level in the supply has to be at least as high above the carbs as the level is in the tank when mounted on the bike. The bowls should fill up and no fuel should drip out anywhere. Be sure to angle the carbs like they would be on the bike too. My experience is the same as DD's as far as Mikuni (EDIT- not just Mikuni's, but they do seem to be worse) fuel valves sticking when first assembled. Even polished or new. Seems like just a few minutes of successful seating is all it takes to become trouble free, but they do tend to stick at first for some reason so you might have to fuss with them a bit at first.

I would add that I can not imagine it possible for fuel to somehow add to the crankcase oil volume while the engine is running even remotely well - as in cam timing is off substantially. Running it so rich that it hardly can be kept running at all would take many many hours of running to add enough fuel to be reasonably measured as added to the oil volume, so I have to think if it is indeed gasoline being added it has to be happening when the engine is not running. Seems like there would also have to be some sort of crankcase venting problem in order to create enough negative pressure in the crankcase to suck fuel down past the rings assuming there would ever be enough fuel to do so in the combustion chamber with the engine running.
 
Tune-A-Fish said:
and then check to see if the floats are set right by holding the drain tube next to the carb and see how high the fuel is in the tube with the petcock open and the drain screw open, should be just below the gasket.
Click to expand...

Sorry guys, the stock Keihins on the 360 dont work that way. The bowl drain screw simply drains w the screw. The overflow w drain tube is separate.

cant check fuel level w a tube. (god knows I wish I could.)

As long as the overflow tubes are clear and functional and the bike is parked on remotely level ground fuel cant seep into the engine.

Ive had fuel POURING out my overflows. When an aftermarket float needle had burrs on it, preventing it from closing at all.
 
trek97 said:
Sorry guys, the stock Keihins on the 360 dont work that way. The bowl drain screw simply drains w the screw. The overflow w drain tube is separate.

cant check fuel level w a tube. (god knows I wish I could.)

As long as the overflow tubes are clear and functional and the bike is parked on remotely level ground fuel cant seep into the engine.

Ive had fuel POURING out my overflows. When an aftermarket float needle had burrs on it, preventing it from closing at all.
Click to expand...

Yep. Just don't do it! haha. There's been very few out of the hundreds of carbs I've cleaned that actually needed new needles. Typically it was because the PO garbled them all up with pliers or similar objects that destroy soft metals :)

The only way to "check the float height" or fuel in these is to have the carbs off the bike, put them at the angle or level they should be at, and drop a bowl (carefully) and physically see the level in there. Did that on an old KZ900 when I didn't have that fancy kawasaki fuel level tool that fits into the bowl screw so nicely. Let us know how it's going OP.
 
Thanks for all the input guys!

I will remove and inspect the carbs at the weekend.

The bike runs well, and it really does seem that the oil level rises on even a brief run.
Nothing comes out of the overflows

The carbs are not the originals, were supplied with the bike which was a half completed project.... So I suspect this problem has always been there with these carbs.

I will check:

Overflows blocked?
Float valves clean/ridged
Test setup on bench without valves to check overflows
Test setup on bench with valves

Will post an update , prob with pics to assist diagnosis!

Thanks again

Steve
 
Quick update, I couldn't resist taking the carbs off......

Overflows are not blocked, can see right through both tubes.
One of the float valves is perfect, the other has a stuck/corroded 'tail spring'
Both valves have clean cones where they close with the seat
Both seats are clean too.

The carb with the stuck 'Tail spring' is the right side, and the right hand inlet manifold rubber is wet inside with petrol, so this seems to be the problem?

I'll buy a new, genuine!, float valve.
Reset both float levels
Rebuild
New oil

Look out for next update!

Steve
 
There it is! The stuck spring will cause your misfortunes!

Now. Shoot a picture of that one. It's probably just varnished in place. You can put it in hot water for a while. (rubber tips on these one's right?) so not TOO hot!

Or soak in some carb cleaner spray. I usually can use a sharp pair of wire cutters/nippers and can "pull" it back out VERY EFFING CAREFULLY. Otherwise, buy some OEM needles and call it a day. Might as well get both. Don't NEED the float valve if you buy OEM, just the needle technically. Unless you want to spend the money :)
 
I did free up the stuck needle valve, but wasn't happy with it so have today received in the post a shiny new genuine Honda set.

New oil too.

So that's my evening sorted !

Steve
 
Sderbyshire said:
I did free up the stuck needle valve, but wasn't happy with it so have today received in the post a shiny new genuine Honda set.

New oil too.

So that's my evening sorted !

Steve
Click to expand...

Win. Good luck and make sure you set those float heights correctly :) haha
 
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