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Old 08-13-2012, 06:37 PM   #7335
Studly Adventurer
Joined: Jan 2008
Location: Green Bay, WI
Oddometer: 768
OK guys, help maybe?

03 640a, 13k miles, no smog stuff, but stock carb, engine, fuel.

My bike is doing a weird fuel thing again at around 185mi left in the tank. I am puzzled by this. It runs like it's cutting out on fuel, but never stops. Not on reserve, probably still 2-3 gallons left (usually when I fill I'm filling 4-4.5gal, tank holds 7.4 or so). I've read about hiccuping, but it does not seem to be like that (maybe it is). Not sure why it'd always come around the same mileage if it was.

Anyway, the bike does cut in/out for a bit, if I just stay rolling it will go away, and tends to be helped a bit if I do a left hand turn (maybe that's just my psychological thing). If I come to a stop the bike will die during this and be a bitch to restart (usually waiting a few min works).

Here's a theory - tell me if it makes sense...
Bike is getting good fuel when the pressure in the tank can help the weak ass fuel pump. When the gas gets lower in the tank, the pump is more on it's own and doesn't keep up so well (I believe it's about carb level in the tank when it does this). The part I don't get is that it doesn't just stop working, it will work again.

My easy solution is just fill up when I'm about 175mi into a tank, but I'd prefer to ride with only about 5 in there max to not be so heavy. It's a lot more nimble off-road when it's not full.

Do I just pony up and replace the pump or is something else out there?
'03 ktm 640a
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