poor mileage/carb issues

2447 Views 22 Replies 3 Participants Last post by mag, Oct 10, 2005

mag

Discussion Starter · Sep 18, 2005

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I'm still having flooding issues with #1 carb, it seems. However, all the plugs read white now. The bike starts with choke, but seems to not catch easily. I have to start a couple of times, then shut off choke once running, then throttle it and leave the throttle lock at 2000 rpm for a couple of minutes. It idles fine, no smoke, though sometimes the idle drops erratically. There is a constant drop of gas on the float bowl drain screw. I couldn't get the float in #1 to pivot totally free. I changed the pivot pin, float, etc. It seems there might be a casting problem with the pinion, ie alignment, so that it causes a 'wow' in the pin or something. It slides in easily, then at the last 1/3rd of the pin length i have to tap it into place. I don't want to break the aluminum pinions by trial/error tapping on the float pin to 'straighten' it? Also, worried about over-sizing the float pin mount holes in the pinions by burnishing them or reaming with a dremel. Suggestions? I'm only getting 28-35 mpg now. Maybe i set the float too high in an effort to seat the float valve? Before i was having fuel leaks, but at least 40mpg.

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mag

Discussion Starter · #21 · Oct 10, 2005

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Thanks, Exavid. I wish it was the case. Just checked the mileage, and got only 31 mpg. I've adjusted the pilot screws to lean it out a bit. The #1 float drain screw still leaks, which is odd, because it was at rest overnight with petcock off. Makes me think it's not from overfilled bowl, but just an old o-ring. Anyway, no smoking, decent acceleration, great idle, but still low mpg. Kinda stymied. Maybe leaning out the pilots will affect mpg next tankful. Can't see how.

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exavid

· #22 · Oct 10, 2005

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mag wrote:

The #1 float drain screw still leaks, which is odd, because it was at rest overnight with petcock off. Makes me think it's not from overfilled bowl, but just an old o-ring.

The carb drain screw would leak regardless of whether the petcock is open since the float bowl is vented. A small leak can make a surprising difference in mileage. How free are the wheels, can you spin the rear wheel when it's on the centerstand and the front wheel when it's off the ground? Any drag there would reduce mileage.

31mpg is a bit low, but maybe it will improve as you ride it. At least is sounds like she's running well now.

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mag

Discussion Starter · #23 · Oct 10, 2005

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I had assumed that the carb drain screw is leaking because of an overfilled bowl. On these bikes, there are no overflow tubes. The plugs read normal now that the aircut valve is in properly, i actually get a little gradation on the plugs rather than bone white. As i said, it's certainly not smoking, the plugs aren't fouled, the timing is spot-on, it idles and accelerates fine. I'll check brake drag, and will also put a new carb drain screw o-ring on. Perhaps pilot screw adjustment will make a diff, though it wouldn't seem so after 3000rpm. It has a newer K&N air filter, which i can see through still. Maybe i should try the stock paper one. Also, could a clogged gas cap vent cause rich running? I don't even know where the vent is in the cap.

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