[Msteele]

Hi all,

I have a carburetor question for you;

What could be the cause of fuel dumping through my manifolds on a 78 gl1000?
I've been having a lot of trouble trying to figure out what is happening to my 3rd cylinder - when I pull the plug for that cylinder while running it doesn't affect the rpms.

I suspect fuel is dumping through the manifold too quickly because cylinder 3's manifold was Ice cold to the touch while running; I actually found fuel sitting in the combustion chamber when I removed the manifolds to get at the carburetors. Not a little bit of fuel - It was completely full. This problem also happens intermittently on cylinder 4 when the bike is leaning to that side and running.

I thought that the vacuum piston was hanging up on the cap (It has a mean ding in it - and upon inspection the piston is definitely rubbing on the inside of the ding), so I replaced the the suspect one with a very clean one from a 79 carburetor I have. It hasn't corrected the problem!

I'm intending to rebuild the 79 carburetors to use with this bike, but would like to have it running in the mean time.

Compression is good on all cylinders: 160-175. Cylinder 3 is the 160. Spark is great.

Do you guys think I should just focus my efforts and energy on rebuilding the 79 carburetors, instead of getting hung up on the problem in the 78s? I'm learning a ton through trouble-shooting; by every measure I'm a complete novice though. Is it a stuck float? Can I test for that? Please HELP!

 

[rpeters549]

Sounds like a float in the carb is stuck so the flow of fuel never stops.

 

[trashtruck]

i agree, float probably hanging up. my opinion, rebuild the 79 carbs now as your old ones will have to come out anyway. remembering to turn off the fuel at the tank valve should help keep excess fuel from flowing.

 

[glhonda]

If you suspect a stuck float, simply pull off the intake tube and see if gas is running out of the carb throttle chamber.
A cold intake runner means there is no combustion taking place (you already knew that by pulling the plug wire with no effect). But it doesn't necessarily mean too much fuel. Too lean a mixture causes a lean misfire, and no combustion.
I suspect from your description, it probably is a bad needle and seat and/or float level.
In any case, you'll have to remove the carb rack to investigate. Try swapping the plugs before you break it down, though. It could be as simple as a bad spark plug.
Check your floats carefully for fuel intrusion. If they don't float, they're not floats.

 

[rpeters549]

Check your floats carefully for fuel intrusion. If they don't float, they're not floats.

Yup- those would be called 'sinks' and they are only good in the kitchen and bathroom!

Also, when you say spark is great, I assume you mean to the fuel filled cylinder? As mentioned above that plug, or wire, could be bad.

 

[Msteele]

WOW, this forum moves fast!
Thank you all for your your responses. I'm sorry for my slow replies...raying:

rpeters, you got it - spark is good to the fuel filled cylinders. I suspected ignition at first and changed the coils and then swapped some from another bike just to make sure. The problem persisted, though I could still see a good spark on that plug with every set of coils.
I thought it could also be something in the Dyna ignition because #4 was firing but more weakly than 1 and 2. I knew that was a longshot, but the wiring on the bike was a bit messy, so I thought something might be bad. I don't believe it's the problem anymore - though I do have another Dyna in good shape that I can install; I just don't think it's the problem, because nothing I did had any effect. Modules seem fine, and spark is good on all plugs.

glhonda, I know it's dumping fuel, because the combustion chamber is completely full of fuel, and the manifold is ICE cold while running - I believe the excess fuel flowing is actually cooling it off. There's even fuel dripping out of the joint between the headers and the mufflers. I don't think that the amount of fuel I'm seeing could be accounted for by a lack of combustion. I'm not very sure about any of my conclusions or assumptions as I'm a bit of a novice, but I think my reasoning is sound here.

One other relevant behavior I forgot to note earlier: when I shut the petcock off and burn off the remaining fuel in the system, the problem cylinder starts to fire as the other cylinders finish firing. I believe the problem cylinder is beginning to burn through the pooled fuel in the combustion chamber at this point and carrying the engine on despite the dwindling of power from the other cylinders.

So I agree it's a stuck float, and I'm ordering a kit (as soon as I can figure where I put my wallet. I swear it's in my shop somewhere...).

In the mean time I just soaked the 79 carbs in hot soapy water for a day, and starting to dig into them. They are REALLY grimy an covered in black paint for some reason. I just hope everything is there when I open it up!