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| Joined: | 03-12-2005 |
| Location: | Kingman, Arizona USA |
| Posts: | 532 |
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The valve has to seal tight against a pressure of 2.5 psi, which is equivalent to a 5-foot-high column of water. Just holding it under a faucet may not be an adequate test.
"The floats are water-tight, so no problem there."
Not necessarily a meaningful test, as gasoline may penetrate even when water won't (due to its higher surface tension). Weigh the float, if possible, or balance it against one from a carb that is known not to leak. IIRC, a good float weighs about 14.0 grams.
"I'm going to get my calipers from work and check the float height on Monday. [...] What could cause the float to get out of adjustment, if that's my problem? "
I don't know of any mechanism by which the float adjustment would change in service. If it's wrong, assume it was improperly set.
"What else could be causing my problem? [...] The gasket around the float bowl was intact; the leak was not from there."
Mitch Ware mentioned the o-ring on the brass/plastic plug at the bottom of the float bowl. This is a common place for leaks especially if there's any damage to the bore for the plug. These o-rings are offered by the usual suspects, as well as being a standard size that should be readily available locally.
Other possibilities include a cracked rear carburetor body or float bowl, badly damaged threads for the fuel inlet valve, lack of gasket between valve and carb body, loose fit between fuel inlet pipe and carb body, and something wrong with the start enrichment ('choke') circuit in the front carburetor that would dump fuel into the rear carb through the connecting hose. And finally, any one of the hoses attached to the fuel tee could have a pinhole leak or might not be sealing properly.