[mag]

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I just discovered where my #1 carb is leaking: right where the carb joins the air chamber. According to randall washington (randakk.com), there are special fuel o-rings on each carb where they join up which are overlooked during rebuilds, and harden over time, causing leaks. I presume this is why i see fuel inside the air chamber of the carb plenum!? Would this also cause an over-rich condition/plug sooting? I just got 45mpg, but the plug is still black. Will replacing this seal deal with the over-rich condition as well as the leak?

 

[exavid]

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mag wrote:

I presume this is why i see fuel inside the air chamber of the carb plenum!? Would this also cause an over-rich condition/plug sooting? I just got 45mpg, but the plug is still black. Will replacing this seal deal with the over-rich condition as well as the leak?

It's hard to see how you could have a major leak and get 45mpg. If a carb is leaking into the air box it seems to me the leaking gas could be drawn in by any carb not necessarily the one leaking, so the cylinder with the black plug might not be the one with the leaking carb. Either way I'd sure assume Randakk wouldn't mention the seal if it wasn't important.

 

[mag]

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Thanks, Paul. Well, how can i have a black plug and still get good mpg?

 

[exavid]

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That's what I was saying in the previous post, I don't see how you can have a serious leak with 45mpg. Have you tried swapping the plugs around to see if the black cylinder plug moves? Just on the off chance the plug might have a problem. If it were my bike, I'd get the new seals in and ride the thing for a few hundred miles without looking too closely at things and then take another look.

 

[mag]

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I put a new plug in yesterday. Today I put in some MMO, filled up, adjusted the idle mixture screws. Rode about 40 miles. Checked the plug, it's black. But i got 45mpg in the interim. Idles great, pulls great, no smoke or backfire.

 

[exavid]

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So... Ride like the plug wasn't black! If you hadn't looked at it you wouldn't have known it was black since everything was working so well. Hell maybe I have a black plug, but since my bike's performing well I don't think I'll look!

 

[mag]

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touché. I just read a guy named Jim Downey's site. He restored a few GL1000s last year. Apparently, the o-ring from carb-to-plenum is where the fuel feed comes in. That makes sense that it would leak profusely there if worn. Secondly, if the o-ring around the float valve is worn or too small (as with aftermarket valves), it will cause flooding in the bowl at idle, which is also happening. Think i'm gonna replace the remaining three float valves with the old OEM ones off my old carbs to rule out that issue (they also have fuel inlet screens on them), and also all the carb/plenum seals while i've got the suckers off.

 

[englishted]

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Mag, you would probably easily get 50mpg if that one plug wasn't running black.

 

[twisty]

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mag wrote:

I just discovered where my #1 carb is leaking: right where the carb joins the air chamber. According to randall washington (randakk.com), there are special fuel o-rings on each carb where they join up which are overlooked during rebuilds, and harden over time, causing leaks. I presume this is why i see fuel inside the air chamber of the carb plenum!? Would this also cause an over-rich condition/plug sooting? I just got 45mpg, but the plug is still black. Will replacing this seal deal with the over-rich condition as well as the leak?

Mag, those "O" rings that Randakk is talking about causes external fuel leaks not internal carb leaks. Are you sure the choke enrichener is closing off completely on that #1 carb? Usually when there is fuel in the air plenum but no other signs of carb leakage that means either an intake valve is starting to leak & causing a fuel spit back into the manifold or a camshaft lobe is starting to wear altering the intake valve timing. Is your cam belt timed correctly on that #1 side?

Twisty

 

[mag]

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Twisty -- there IS an external fuel leak, right at the carb-to-plenum for #1. There is only 36k miles on this bike, i don't think it's camshaft/intake valve wear. Cam timing is perfect, as are clearances. You might be right about the choke enrichener not shutting off on #1. Would i just move the choke linkage and observe through the carb intake to see the butterfly move in tandem with carb #3? Remember, this is intermittent -- sometimes no external leak, and plug reads normal. That's why i suspect float flooding, which is also leaking back at o-ring.

 

[Goldwinger1984]

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Mag it is conceivable that your fuel economy is good in spite of the plug looking black if the over rich condition is caused the float level being set too high.

During cruise conditons at high speed the fuel is fed into the engine and burned at the proper rate because fuel is flowing through the carb, but, when you slow down the fuel accumulates in the float bowl and if the floats are too high this will cause an overich condition that will only be apparent at idle and very low rpm. If the needle valve does not close at all it can also affect higher speed operation.

The correct way to do a plug check is to wind the engine out to the top of third gear, kill the engine, pull in the clutch then pull the plugs to have a look.( Do this only on a deserted road or a dragstripbecause you will reach high speed.)This will show how they are burning under load.

I agree with Twisty regarding the o ring as it seals leaks to the outside and I would also check the enrichener to determine if it is leaking.

Vic

 

[mag]

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Thanks, Vic. You're explanation makes total sense re: inspecting black plug at idle vs. load. The float in #1 is set exactly at 21mm when the tang contacts, but doesn't compress, the float valve. Maybe i should go even lower? I've got my old OEM valve/needle in there with an old o-ring on the seat, so perhaps that is leaking? How do i check the choke enrichener on that carb? I'm definitely going to have to replace the fuel o-rings as they are leaking externally -- sometimes at carb #1 and sometimes #4.

 

[exavid]

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Goldwinger1984 wrote:

I agree with Twisty regarding the o ring as it seals leaks to the outside and I would also check the enrichener to determine if it is leaking.
Vic

You guys sure that the external leakage can't get sucked back in when running?

 

[mag]

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Since #1 is the only culprit, and the only float i've adjusted, and i've replaced the float valve/needle/float/pin, i think my float height measurement is off. I've been measuring from the raised lip of the carb body, not from the float bowl gasket lower down. According to randakk.com: "(float height) is measured from the bottom edge of the float to the raised lip adjacent to the carb body fuel bowl gasket surface." So, is this the highest point of the carb edge when the bowl is off, or the lower edge where the gasket sits??

 

[exavid]

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mag wrote:

Since #1 is the only culprit, and the only float i've adjusted, and i've replaced the float valve/needle/float/pin, i think my float height measurement is off. I've been measuring from the raised lip of the carb body, not from the float bowl gasket lower down. According to randakk.com: "(float height) is measured from the bottom edge of the float to the raised lip adjacent to the carb body fuel bowl gasket surface." So, is this the highest point of the carb edge when the bowl is off, or the lower edge where the gasket sits??

Sure sounds to me that he's referring to a raised portion of the casting aboveand just outside of where the gasket lies. Is there a raised edge around the outside or inside of the gasket's edge? If the gasket has been used before and is pretty well squashed, I wouldn't think there'd be that much error if you used the surface of the gasket as a reference, it should be pretty much the same on all four carbs and it wouldn't be that much difference.

 

[mag]

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well, looks like i've got the float height correct. It must be the valve seat o-ring leaking or the float sticking on the pivot pin. It seems the float doesn't 'drop' up and down as smoothly as the other carbs. This is the only thing i can think of. I'll replace all the rubber with new and see what happens. Damn frustrating.

 

[exavid]

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mag wrote:

It seems the float doesn't 'drop' up and down as smoothly as the other carbs.

Check the action of your float with the pivot pin tilted, not parallel to the ground. Sometimes a float will bind, if it isn't moving smoothly it's very likely to hang up or at least allow the fuel level to vary. I've seen a couple of carbs where the float would work perfectly when the carb was level but hung up a bit when tilted slightly. Very annoying when you're working with a gas tractor on a side hill. I think you're going to need to figure out why that one float operates differently than the others.

 

[SilverDave]

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 Clearly... Exavid has driven ,and tuned every conceivable vehicle type ,on the planet !!!!! Tractors, now.. I am beyond  impressed/forums/images/emoticons/shock.gif !!! Silver/forums/images/emoticons/emoticonsxtra/cooldj.gif

 

[mag]

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By tilted, Paul, you mean stand the carbs up on end (resting on the intakes) vertically, then tilt them off 90º angle slightly so the float tang swings away from the pin, to check smooth (natural) float movement? Poor movement would confirm why my bike bogs/stalls when running and put on the side stand occasionally.

 

[exavid]

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Yep, that's what I meant.