Topic: Gasoline and Engine Oil under bike, big time.

[NateMinn]

Hi,
This is my first post and I am a new member here.
I have two bikes, an '81 750 super sport, and my first love, a '77 cb750Four.
So, recently I found a puddle of engine oil and gasoline under the bike.
I rode it the night before. Seemed to ride fine.
This was more than just a drip. It appears it was backing out of a single carb, I think #1 or #4.
Any ideas here? I'm thinking a blown head gasket?
Any tips are greatly appreciated. I've already prepped the engine to pull it.
Bike has about 55,000 miles. I got it at about 30,000.
Thank you!
Nate

[the technological J]

is the bike smoking? you could have a stuck float to explain the gas but i would try to find the source of the oil it might just be a seal.. theres 2 on the shifter one on the kick start  you might not need to pull her out unless you wanna rebuild her

[ekpent]

Do you manually turn off your gas tap when you are done riding ?

[MCRider]

Do you manually turn off your gas tap when you are done riding ?

Right. SOP it to turn off the manual tap at the end of every ride. I would turn it off before shutting the engine off, that way the bias is to have less fuel in the bowls than normal. Left on, a stuck flaot will overflow out the carb, obvious. Fuel running down the engine can dilute the greasy mess around the sprocket and drip on the floor.

But also the fuel can drip into the engine and down to the crankcase where it will dilute the oil. Once you get it sorted I strongly suggest changing the oil.

Remember SOP is to turn off the fuel tap EVERY time, and park on the centerstand, so the floats don't lean to one side and get stuck.  If the centerstand parking is hard to do, I slip a board under the sidestand to stand it up closer to vertical.

[Johnie]

Sounds like stuck float. Regarding the oil...any chance you could have overfilled the oil tank? Check it when warm and see where it is. Has happened before.

[NateMinn]

Wow, this is great. Thank you all!
So, I have not been turning off the fuel (for the past 3 years) on this bike minus winter when I do drain the carbs.
And I know the leakage stopped when I turned off the fuel.
I will be turning off fuel after each ride. I didn't realize this was SOP but for bikes with bad carbs.
It is the oil that really worried me. I'm going with MCRider that the fuel ran into the crank case and onto the street.
I will be changing the oil before I do anything. I should also note, the bike leaks very little oil at all. A little from the head gasket, but very minor.
I think the engine stays in.

Thanks again, you all saved me going far beyond what needs to be done.
Question, this float bowl has stuck in the past?
I had the carbs cleaned/tune extremely well by a certified Honda cycle shop about a year ago.
Any thoughts on prevent the carb, my #4, from sticking?

Thanks again!
Nate

[MCRider]

Its not so much that it ran into the crankcase but rather behind the countershaft cover where all the yucky chain grease is. It would have diluted that yuck and it ran out onto the street. Why would I suggest this? experience.

Still that's outside the crankcase. If the gas also ran towards the engine thru the carb throat, THAT would have run down the cylinder walls into the crankcase, However that's where it would stay, it would not become apparent otherwise by leaking anywhere. That's why you have to assume that has happened and change the oil.  Again, experience.

As to the sticking float bowl, most common cause is parking it on the sidestand. Most common fix is standing it up from the sidestand and tapping on the side. Especially if your pretty sure it is otherwise clean of sticky shellac.

AS to the SOP turnoff the fuel tap. Its in the owners manual, usually. More modern bikes have vacuum operated fuel taps which turn themselves off when the engiine stops running. These came out in 1980 or so. If your expereince is only with newer bikes you wouldn't run into this issue. Goes with chokes on the carbs, other such archaic designs. Consider turning the fuel off as you approach your garage. Let the engine run for a minute with the fuel off. This will pull the fuel level down a tad. Jut me but it feels better that way.

Be sure to turn the fuel back on when starting and you may have to wait a moment for the fuel level to come back up. Back on our old racebikes, many a racer has been left on the grid forgetting to turn the fuel back on. It'll start and run for a bit but not long.