Topic: TURN OFF THE DAMN GAS!!!

[Bob Wessner]

I agree, gas in oil..not good! Just curious.

[eldar]

I still have never had this problem. Even accidentally leaving the fuel on for a month, I never had a leak. But then the 78 750k has a different petcock thant the earlier 750s I think. maybe that why.

[Einyodeler]

I left my petcock on at work one day and on the ride home my oil light started flickering at stop lights and got progressively worse by the time I got home.Fuel in the crankcase=tosted bearings!

[cb650]

I am glad someone brough this thread up, I always leave the petcock on the 'on' position for days.  Luckily i've never experienced a fuel leak.


Rob

Your 650 should have a vacume shut off too.  Unless they are like mine and have been removed.


                    Terry

[Raul CB750K1]

My carbs never leaked even when forgetting to turn the gas off for days. But his morning I saw a small stain in the floor... guess what: GAS. I forgot to turn the gas off. But the stain was not under the drain tubes. I was in a hurry to work, so this afternoon I'll check where does it come from.

It could be the airbox, or maybe through an open valve through the exhaust, but I bet level should get real high to go through the exhaust. I had a problem a while back with the petcock, so maybe it was just leaking over the engine and from there to the floor. I hope I don't have to change the oil, the drain tubes were surgically clean because I rebuilt the carbs about 2 years ago.

[MotoDave]

BEWARE, it may not be the float sticking at all.  Long story short, I had an occasional problem with my carb bowls leaking out the overflow. I would readjust the float level a bit lower, then no fuel at all. The carb would either flow no fuel or would leak out the overflow.  It turned out that there was leak between the aluminum bowl and the brass overflow tube.  The floats were fine.  To test, take the float bowl off and put fuel in it almost all the way to the top and see if any fuel weeps out the overflow.  I had to go through 3 of them before I found a good one.  It looks as if the float is stuck open, but it's not!

[dusterdude]

dave,also my k1 has the bowls with the tubes in them 3 of mine are cracked and leak out of the overlfow,i just run hose off the overflow and run it up above the carbs and that takes care of the problem.

[TwoTired]

dusterdude,
Doesn't what you are doing defeat the purpose of the float bowl stand pipes? Which is: to keep overflowing gas from filling the intake runners, piston cylinders and the crankcase with gasoline from a stuck open float bowl valve?

[dusterdude]

no,the gas is running from the cracked stand pipes.the float level is fine and no gas is going into the engine.good question tho.

[TwoTired]

dusterdude,
I'm only saying this to help you out.  Please do what you feel is correct.

The stand pipes in the float bowls are safety/backup devices to prevent fuel from diluting the engine oil in the event of a float system failure.  The drain tubes would then route such overflow away from potential ignition sources on the bike proper ie: exhaust or hot engine cases.

I understand your safety devices (Stand pipes) are broken and accept that a temporary solution is to route the drain tubes higher than the normal fuel level in the carbs.  This is an efective short term solution.

Just be aware that if your carb float system fails, float or valve, or a small piece of rust scale or dirt blocks the float valve from closure, while your safety bypass is in place, there is the potential for the fuel in your gas tank to drain into the crankcase of the engine instead of a puddle under the bike.  If this, then, goes un-noticed, operating the engine may severely shorten it's operational life.  Then the rest of us SOHC4 aficionados will have another source of spare parts, (well, except for the engine, anyway).

Best of luck!!

[Raul CB750K1]

Confirmed: I had an overflow into the cylinder. I tracked the small stain in the floor, it was coming from the engine block. And there from the airbox. Airbox had gas on the bottom and the filter was soaked.

I removed the plugs, none of them was wet. Put the killswitch in off position (for no reason at all), cranked the engine and cylinder #1 shot a dose of fresh gas on the wall. Cranked a little more, plugs back in place, and with petcock off run the engine until the carb bowls were empty. For the life of me I say that I couldn't smell any gas in the oil tank. It had that typical oil smell with fumes, but no oil gas at all. Should I have to change the oil?

But please somebody explain this to me: I bet my lef testicle that the overflow tubes are clean. How come that the fuel didn't go through the overflow and went into the cylinder and airbox?

Raul

[TwoTired]

Raul,
Have you confirmed that the overflow pipes and tubes were clear?

I say this because I have found mud dawbbers or some other insects that have built nests in and solidly plugged up the drain tubes!

It may also have something to do with parking on inclines and/or sidestand vs mainstand use?  Further, there is the lean angle of the bike while on the sidestand to consider.  Stiffer suspension springs that increase ride height also increase the parked lean angle.  And, that puts #1 cylinder much lower than the rest.  I've also seen worn and bent side stand pivots that also increase the lean angle while parked on the side stand.

Also note that gas in the crankcase won't get to the oil tank in the 750 until the engine is run due to the dry sump type oiling system.  Therefore, the gas in the oil smell could be delayed 'til after the fact.

Cheers,

[Raul CB750K1]

Lloyd, thanks for your reply. I'll check and blow through the overflow tube, but I would bet my other testicle that they are clean.

The bike was on the centerstand; I run the bike on idle and giving an occasional 3000 rpm every now and then till the bowls were emptied. It took about 5 minutes, so I guess it's time enough for the oil to recirculate and go to the oil tank. Why the gas didn't go through the tube is a mistery. Somebody should have gave me that f&%cking bike bell to protect me from those evil spirits....

[Terry in Australia]

Hey Raul, when you send your testicles to Lloyd, can I have one? Ha ha, if you've got fuel in your airbox it's because your overflow tubes are blocked.

The overflows sit a fair distance higher in your float bowl than the floats will alow the fuel level to reach under normal circumstances, so if you get a stuck float valve and fuel fills the float bowl, the overflow tubes allow the surplus fuel to run away.

In your case the fuel can't exit via the overflow tubes, so it continues up via the main jet and enters into the carbs venturi, where it runs down into your cylinder, and back into your airbox.

To fix it, you'll need to remove your float bowls and blow/poke the crap out OFF the carbs, or else you might damage them, and add more muck into your carbs. I think you've got my address mate, so if you could pop that "knacker" into an empty vegemite jar and zip it over to me, I'll get it "Bronzed" and hang it offa my key chain, ha ha! Cheers, Terry.    

[TwoTired]

Actually, you can put a mity-vac hand pump suction device onto the float bowl nipples.  If it won't clear with 40 psi suction, then you will have to remove the bowls to clear the stand pipe.  Remember to open the drain screw for the 750 carbs.

Terry's right, you don't want to push crud into the float bowl chambers.  But, once disconnected, you can use compressed air on the flexible drain tubes.  I had to crush the packed in mud with pliers before it would come out, though.

Er, please keep testicles in the factory stock location.  I walk funny enough as it is.  And, three's a crowd, don't know?

Cheers,

[Raul CB750K1]

I'll come back when I check it, but I personally rebuilt the four carburettors, and not by drowning them in carb cleaner, but using spray carb cleaner and compressed air. I checked ALL the jets, idle passages, gas feeding, and of course the overflow tube, that's why I did such a "bet". Common sense dictates that the only reason gas would reach the ventury is because the overflow is blocked, but the overflow rubber tubes are also new, so I know they are not clogged.

There was a topic some days ago about the routing, and I said that they go through a bracket in the swingarm. I could be that they got pinched somewhere there, so that could definitely be a reason.

I'll come back with the feedback.

Raul