Help! Leaking fuel...

[skubasteve!]

Hey guys,

Im a total noob to bikes, so hopefully this is something stupid/easy fix. I went to hop on my 78-750 and go for a ride today, but it died after I got out of the driveway.

I checked the tank and thought I was maybe out of fuel. So I hopped in the jeep and went and got 2 gallons. Bring it back, fill up the bike and it starts right up, then, I look down and its pouring out fuel from underneath. I appeared to be coming out of one of the black tubes. It wasnt just a little drip, it was coming out pretty good. So I shut her down and put it back in the garage.

I did not overfill the tank (at least i dont think i filled it too high). I have only put on 100 miles since I got it back from the mechanic, please tell me I dont need to sink more money into this machine!

Thanks in advance

[chuck hahn]

By BLACK TUBES are we talking the boots between the airbox and the carbs..between the carbs and the engine ..or the fuel line coming down from the fuel cock on he tank..or from the overflow drains under the bike...more specific the info easier to diagnose.

[skubasteve!]

Sorry, it appeared to be coming from the drain tube i suppose. It was the one that runs down towards the bottom of the frame by the middle of the exhaust pipe is where the end of the tube is.

[bonanzadave]

please tell me I dont need to sink more money into this machine!

I dont want to be the bearer of bad news but.......ITS A 1978 !!! Yes, you will have to do some periodic maintenance that will require opening up the wallet .

As for the fuel leak I would watch it with a full tank or you may have that fuel on your garage floor. It only leaked when you started it ? Could be the petcock fuel line to the carbs is leaking. When you start it vacuum opens the petcock and allows the fuel to flow.

[chuck hahn]

Could be the petcock is malfunctioning..could be a bad float ( pinholes in the metal ones weigh them down) Could be a bad float needle valve..rubber tips get "ringed out" from sitting against the seat..could be a miriad of small problems..Trick is to understand the symptom, where EXACTLY the fuel is leaking from and then trouble shoot. Float height adjustment will cause the carbs to overflow if not properly set as well. Side thought..fuel tee and transfer tube Orings can be leaking also...

[skubasteve!]

Thanks guys, I will try to take a deeper look into it later. If it helps I had just got it back from the mechanic who redid the carbs and float needles and all that jazz. Its been great for the 99 miles I put on it so far.. til now.

[tkent02]

Thanks guys, I will try to take a deeper look into it later. If it helps I had just got it back from the mechanic who redid the carbs and float needles and all that jazz. Its been great for the 99 miles I put on it so far.. til now.

That was your first mistake, there are NO mechanics that will take the time and effort to do what a thirty year old bike needs without charging you many times what the bike is worth to do it.
If you can't do the required maintenance yourself, get a newer bike, or learn to do it...
Your carbs need work, your mechanic scammed you. Get in there and make it right.

At least the petcock is working somewhat, or the leak would not have stopped when you shut the engine off.

Do all the things on Cliff's list before you ride it.

[chuck hahn]

Tom is right..rebuild the carbs..only way to be 100% sure they are right.. If you dont want to do them I suggest you PM Chef or any others here that rebuild them and youll get top notch work at a far more reasonable price than anywhere else.. They are fairly straight forward carbs being VM 26s..if they are the stock carbs that is.

[skubasteve!]

Thanks for the responses guys. I guess I wont get much, if any riding in for the rest of the season if I have to remove and take apart the carbs. With the kids and the old lady working nights, I just dont have the time for such a project.
Looks like Ill be saving up some money over the winter to buy something a little newer that doesnt require as much maintenance. Does anyone have any other suggestions before I have to go diving into this? Im a bit nervous about this carb job as I am not very mechanically inclined. Would it help if I tried to get a quick video?

[chuck hahn]

PM chef (BILL) hes very reasonable and the turn over wont be that long...just sayin.

[Lambo]

leaking gas

Mine was doing the same thing, but I had to get a new clamp for it and it stopped. I also had Chef re do my carbs and they work great untill the liner I had put in my gas tank started comming loose.

[robertbarr]

Your VM's are wonderfully simple little animals, and are known to function for a generation or so without a hint of trouble.

A leaking inlet valve isn't necessarily an indication of a poorly done rebuild. An aging valve needle can look and test fine, and then leak a few weeks later. You could also have some rust and/or debris in the fuel tank that can lodge in the way of the needle, causing a temporary leak.

It sounds like the petcock is working fine, but it's a simple enough test that it should be checked anyhow.

[skubasteve!]

This could definitely a possibility. If this is the case, is their any way to loosen or even flush out the debris with fuel, without having to dissasemble the carbs? Could I drain them, then turn petcock on prime and tap them with the handle of a screwdriver or something?
As stated I did have the carbs rebuilt by someone whom "specializes" in older UJM's. He Cleaned carbs, replaced bowl gasket and fuel needles. Synced, checked adjustments set float heights. Im not saying he didnt mess anything up, just thinking that something else is the problem.

Thanks again.

Your VM's are wonderfully simple little animals, and are known to function for a generation or so without a hint of trouble.

A leaking inlet valve isn't necessarily an indication of a poorly done rebuild. An aging valve needle can look and test fine, and then leak a few weeks later. You could also have some rust and/or debris in the fuel tank that can lodge in the way of the needle, causing a temporary leak.

It sounds like the petcock is working fine, but it's a simple enough test that it should be checked anyhow.