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Discussion Starter #1
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.
 

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AS the problem is occuring on all cylinders(?) :huh:its unlikely to be something in the carbs my check list would be mostly electrical i.e...

ECU and connector
Fuel cut relay (next to the ECU)
Fuel pump
All connectors concerned with fuel control
Happy hunting:)
just one further thought to contradict what I said above was the bike left to stand for a long period with fuel left in the carbs?If so it may have evapourated out and lacquered up the jets which will effectively make them smaller,spraying in a good dose of carb cleaner could be your solution.
 

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Discussion Starter #3
All excellent suggestions that I will try to explore tonight. There was no sign of any varnish or foreign matter inside the carbs although I do not know whether it was left sitting or not and as you suggested it is a problem affecting all cylinders simultaneously. Thanks for your suggestions
 

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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.
Get a new air filter as I'm fairly sure you shouldn't oil it.
Have you tried new spark plugs?
 

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Discussion Starter #5
Actually K&N airfilters do require oil (which comes with the filter) to trap dirt but I might have gone a bit overboard with oiling it, I'll clean it off and try that before replacing it with a stock filter. I have not replaced the plugs yet because it runs very well at low rpm and basically not at all at high rpm so I think this is a bigger issue than just the plugs. Not to say that plugs aren't on the menu at some point in the near future. Thanks for your input.
 

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Actually K&N airfilters do require oil (which comes with the filter) to trap dirt but I might have gone a bit overboard with oiling it, I'll clean it off and try that before replacing it with a stock filter. I have not replaced the plugs yet because it runs very well at low rpm and basically not at all at high rpm so I think this is a bigger issue than just the plugs. Not to say that plugs aren't on the menu at some point in the near future. Thanks for your input.

Ah yes, I missed the bit about the K&N :)
I'd go back to OEM air filters myself.
I've had plugs run fine until they're under load at high rpm. If you're going to take them out to check them you might as well replace them - it's never a bad thing to do.
 

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Discussion Starter #7
You may be correct on the spark plugs, since I have no idea what's wrong it's a good place to start eliminating potential problems. Cheap and easy, I'll change them in the next day or two. I have cleaned the oil off the filter as well and will try it to see if I get any difference at all, if it improves even moderately I'll get a stock one. I also pulled apart all the electrical plugs and checked them before plugging everything back together with dielectric grease. I really hate to put it all back together with no real idea if I have actually corrected the problem or not, however we have a long cold winter looming ahead here so I should have lots of time.
 

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Discussion Starter #9
I would like to thank both you guys for the input into this problem. When Bladeracer said "Get a new air filter as I'm fairly sure you shouldn't oil it" he actually hit the nail on the head. I put the bike back together tonight, carefully removed the obviously very excessive amount of oil I had put on the filter and went for a test drive. The bike pulls cleanly to redline and all seems well. It doesn't make me feel very bright but live and learn I suppose, I would not have thought that over-oiling the filter could have such a dramatic affect on the running of the bike, I will get a new OEM filter tomorrow. On the bright side I had a nice tour through the fuel system and all my electrical plugs.
Again, I appreciate the assistance even though it was self induced. Part of my penance is that it was only -2 C outside and snowing very lightly, stiff weather for spinning motorcycles down the highway, at least the roads are dry.
 
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