Join Date: 10-25-2010
Location: Calgary, Alberta Canada
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F3 bogging above 5,000 rpm
I have not seen a similar problem listed on this site. I recently bought a 1998 F3 for my daughter with 35,000 km (21,000 miles) on it. A short (no insurance) test drive at low speeds seemed fine. After bringing it home and doing some maintenance (oil & filter, check valves, service K&N filter) I rode it and it bogs badly above ~4,500 to 5,000 rpm. It starts and drives well at low rpm and can be babied up to higher rpm (with very small amounts of throttle) but large throttle inputs cause an immediate bog and slow down.
Gas tank is clean as are the petcock screens (gas seems to pour out of the tank fine), fuel filter was changed, fuel pump runs on start up (but I don't hear it all the time), carbs are spotless on the inside, the mains are one up from stock (1/4 138, 2/3 140) but it has a Vance and Hines pipe, the air box is all stock and appears to be plumbed correctly with all the air hoses etc. installed, leaving the fuel cap open seems to make no difference nor does putting on the choke, similar bog in every gear but possibly a little bit worse in higher gears with more load, plugs are black but not wet (at least by the time I got home again), it appears to burn no oil and temperature is normal. It revs willingly in the garage but not under load.
My initial impression is this is a fuel delivery problem but I would think that the symptoms would be a bit more variable depending on how much fuel was in the carbs. I did oil the air filter but riding it for 25 km has made no difference at all and I have not tried the bike without it. Same rpm, same bog no matter what I've tried. I am wondering if there could be a mechanical reason for this since it seems very consistent. Any thoughts would be appreciated while I still have the carbs/ airbox off.