Gas pouring from 3 & 4 carbs

[Guest]

Ok, so I'm at the end of a year long build and tried to start the bike for the first time last night with a major fail. I turned the petcock dial to prime, then start to crank and nothing. Then I hear gas start to pour out of carbs 3 and 4 and also drip from the vent tubing between carbs 3 and 4. Once I turned the petcock dial to ON (horizontal) the leak stops.

I've done a full rebuild with all new seals, O-rings, gaskets and dipped everything using the to write-ups off bike cliffs site.

I keep hearing about possible stuck floats, Any ideas?

[Steve]

I keep hearing about possible stuck floats, Any ideas?

Tap those carbs with a heavy screwdriver or a light hammer.

.

[chuck hahn]

Tap on the bowls with a socket ratchet a few times. If they didnt do it before then yup probably stuck float and needles.

[chuck hahn]

Sometimes the bowl gaskets squish out "just enough" to drag and hang up the floats. I have had to open them up a few times and trim them back with a razor knife..problem never reoccured.

[claygs750e]

Ok, I'll try that here in a few. Just for my knowledge do I leave it on prime when first starting or only enough to fill the bowls and then switch the ON? It doesn't leak when the setting is in the ON direction.

[Steve]

You can use the PRIme setting long enough to fill the bowls, about 30 seconds is usually enough when the bowls are dry.

The reason they don't overflow when in RUN is that you have stopped the fuel flow at the petcock.

At least you know your petocock is working properly.

.

[chuck hahn]

If it hasnt ran in a week or so, i set my bikes to PRI and choke then start and once its running I swing it back to ON..but never ever forget that you had swung it to PRI.

[tkent02]

15 - 30 seconds is all it takes. The important thing is not to leave it on Prime.

[JTGS850GL]

Just to make sure, but are you sure you connected the petcock fuel line to the center fuel port on the carbs and not the breathe hose to carbs 3 &4? If you connect the breather hose to the fuel line it will do exactly what you described. Gas will pour from two of the adjacent carbs (1 & 2 or 3 & 4)and will not start. Ask me how I know this. Sometimes it turns out to be the simple things.

[claygs750e]

Ok, so I removed the carbs and checked carbs 3 and 4 since those were the only ones leaking and the needle valve looks ok, height of floats are to spec and nothing dirty anywhere since I previously went through everything already with a fine tooth comb. Before I assemble everything and attach to the bike is there anything else I should look at?

Only carbs 3 and 4 are leaking and only when in the prime mode and when I'm trying to crank it over. When the petcock is in run status nothing leaks.

Thanks

[tom203]

"....carbs 3 and 4 since those were the only ones leaking and the needle valve looks ok, height of floats are to spec "

Ok, but how about the o-rings on those good looking needle seats? And as Steve said, the petcock is blocking flow in "RUN" position (until bike starts).

[chuck hahn]

Are the oring between the two carbs transfer tube good? Are the floats anywhere near close to rubbing on the gasket when it is in place? Are the gaskets (Orings ) on the float seats themselves good?

[JTGS850GL]

I always test them on the bench before installing them on the bike. Put them in a bench vise and level them. Use an axillary fuel tank with the gas level a foot and a half or so above the carbs and fill the bowls.

I'd much rather find the leaking float valve before I install them. It's also nice to be able to verify actual float level by using something like this:




Note that the float level is a tad high in this one. I use the bottom edge of the float bowl flange as a easy reference line. It's about 4.5mm from the top of the flange.


That setup is used to check the float height of one carb, but you could gang the carbs and then verify each float height after. I use the bottom rail to mount everything to. If you have a leaking carb it will be obvious. Much easier to fix the problem while the carbs are not mounted.

On a side note, if you use the same type of line for the vents as you do for the fuel inlet you may want to consider marking them to distinguish them from each other so you don't accidentally connect up a vent line to the fuel tank after mounting the carbs.