Topic: 81 cb650c carbs leaking gas, what to check?

[626]

Got the bike out last weekend to see if I could figure out why my carbs are leaking.

It started leaking last year, at first out the over flow tubes when I shut it off. It would leak a bit then stop, then got worse to the point it wouldn't stop leaking and I had to put a catch under it. So I put in an inline pet cock(I didn't have a pet cock for years without any problems) problem solved. However then it started leaking badly while running, looks like its coming from everywhere.

Last weekend I pulled the tank off and hung a small tank from the bars so I could run it and get a good look at where the fuel is coming from. Started right up and ran fine, but would not leak, running or sitting motor off. Put the tank back on and hit the gas station, fuel running everywhere before I even got away from the pump.

So I pulled the carbs off of it after work tonight and will open them up tomorrow, any ideas of what I should be looking at as a main suspect?

Found my push cable rusted in half, new set of cables on the way. I suppose I should just order a rebuild kit, but thought I should ask in case it is commonly caused by some thing that might not come in that kit.

[Mr. Mike]

Sounds like to me based on what you’ve told us is the trouble is at the fuel valve itself.
*Placing an inline bull nutt shut off solved the problem temporarily. Next...
*Then, it wouldn’t leak running or sitting with the tank off using the remote fuel tank.
*Once using the permanent tank, it leaked like a sieve.

I’d be looking at the fuel valve or it’s connection points (tank or hose).

[tlbranth]

I'm not familiar with your particular model but I can tell you that in the past I've had trouble with float tang dimpling. The needle valve wears a dimply which can hang up the float. With the engine running it'll usually shake itself loose but shut the engine off and it might hang up inconsistently.

[626]

Well it isn't the fuel shut off, the hose or the tank. I can verify that.

I pulled the bowls off today and with the carbs upside down, three of the floats if lifted and dropped had a nice springy landing while the forth just banged against the upper part of the carb. So I'm assuming that the spring in that needle valve is shot. That float also goes up farther than the rest of them.

I guess that it was strong enough to stop the flow of fuel when the very small tank was on it but not the increased pressure of the larger tank. Rebuild Kit on the way, there was some crud in there too. Not as much as I thought there would be. The little plunger that I believe is the accelerator pump has a good bit of fine silt like stuff on it.   I've had the bike for 7 years and have never cleaned them, could have been worse.

[ballinchestr]

I have the same bike, and it had the same problem when I got it. It stopped after I cleaned the carbs, giving special attention to the needle valves and the ports that they go in. If your rebuild kit came with new valves, I'm guessing yours will probably run even smoother!

[tlbranth]

From what I've read here and on the NGW forum, after market needle valves tend to be not too good.

[scottly]

I pulled the bowls off today and with the carbs upside down, three of the floats if lifted and dropped had a nice springy landing while the forth just banged against the upper part of the carb. So I'm assuming that the spring in that needle valve is shot. That float also goes up farther than the rest of them.

I had a similar problem with weak needle springs years ago; I could press the float up with my finger and the flow would stop, but with the bowl installed the carb pissed gas.

[626]

When I pulled the needle valves out, the suspect one's spring doesn't work at all. No action at all, stuck in, hope the new ones work good.

[626]

From what I've read here and on the NGW forum, after market needle valves tend to be not too good.

I hope they work ok. I've been spending a lot of time reading NGW. I have a 86 GL1200A stripped down to the frame and motor, working on a cafe racer treatment for it.

[626]

That seems to have fixed it. Just took it around the block, but it would have been leaking before I left the driveway before. While I was at it I put in a nicer inline fuel shut off, deleted the auto shut off, replaced both throttle cables and did a new chain and sprockets too.

Going to be nice riding to work tomorrow.