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I have an 02 F4i with 4,0xx miles on it, i just did an oil/filter change about 200 miles ago.

I bought it used in December with 2000 miles on it.

For the past few days (100~ miles?) it would occasionally have a hard time starting after the engine had warmed up (sitting in the sun or previously ran), and would kinda sputter around 1100rpm's. Sounds a lot like a misfire or dead cylinder.

If i give it a little rev (to 2000~2500~)rpms it will cough out the misfire and idle just like it normally does.

These recently started right when we started to hit 90+ temperatures and high humidity...

Just looking for some ideas on how to fix it. Going to pickup some injector cleaner etc and see if that helps.

Since the bike had been sitting it appeared when i bought it, i took apart the tank and pumps and looked them over made sure they worked properly and reassembled. Also has brand new air filter.

No performance modifications aside from K&N air filter and a cutoff pipe (performance decrease? :)) Cutoff has a baffle i made to restore semi-stock backpressure levels and lower noise levels.

Recently dynoed with a near picture perfect power curve and 91hp (3000 miles~ with cutoff and no baffle)

idle should be set to at least 1300rpm. 1100 is a bit low.

the combination of a K&N air filter and a cut-off exhaust will dramatically alter your air-fuel mixture going through the engine. a lean mixture will cause hesitations and misfires, especially w/ the throttle closed... so ya, both of these modifications are causing your problem. i highly doubt the baffle you made is helping at all, but is really just adding another variable to this confusing problem.

did the dyno you used spit out a fuel mixture curve as well?? the shape of the power curve doesnt matter all that much if the fuel curve was WAY off as i suspect it is. uve also changed things since then by adding the baffle, so you should probably re-dyno the bike w/ an add-on fuel manager like a powercommander for some real adjustment.... or you could just install a real exhaust.

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Naked 93' F2...... RIP -- 04/12/07
04' 600RR Black - currently stuck between track and street usage
- Brembo Master, Sato's, & Ohlins out back

the pipe and filter have been on the bike since 2500 miles ago, i have a hard time believing that all the sudden a bad a/f ratio is all the sudden going to cause a rough idle.

I'm making a custom exhaust right now, but when it starts rough, after a blip of the throttle it get a real rich smell and then a little puff and back to normal.

I think i may have a fouled plug and am going to replace all 4 plugs tonight. Already running some seafoam through the take, though i doubt that a clogged injector is the culprit especially by the rich smell i get during the stumbling idle.

of course a botched a/f ratio will cause a rough idle. the bike ran 'ok' when the weather was nice, but u said that now temps are up past 90deg and the humidity is high. both of these changing factors affect how your bike idles dramatically, esp since the amount of air and fuel a bike uses at idle is minuscule compared normal riding conditions. higher temps mean less oxygen and inefficient combustion... so you could just be spitting fuel out the exhaust.

your bike is constantly changing. throttle bodies steadily go out of sync, weather and temps constantly change, fuel systems change day to day, valves slowly tighten over time.. etc etc. one day, it wont run right whether or not it was a steady change or a sudden one.

oh ya, hows your battery?? and i do like the idea of changing the plugs.

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Naked 93' F2...... RIP -- 04/12/07
04' 600RR Black - currently stuck between track and street usage
- Brembo Master, Sato's, & Ohlins out back

Battery is fairly new i don't remember the year but i checked it when i bought the bike and it sat on a trickle charger / battery keeper all winter as well.

The thing with the weather changing as well as a previously "lean" run.

Hotter humid air is less dense and actually requires less fuel to run so a previously lean condition would be richened, but not nearly that much. Also the "rich" smell goes away right after the stumble which means one cylinder or more is misfiring. Once the stumble is gone (only takes seconds) the rich smell is gone and back to a "good" smelling exhaust burn. The truth will be told though once i get the plugs out tonight and read them.

plugs appear to be good and read well, not as lean as i thought, actually a bit more rich than i thought.

couple looked to have a light amount of oil on them but i don't think anything to be concerned about, definately a veerry light amount of oil.

the crappy part about reading plugs is that it only gives u an "average" for how the engine is running. if u installed brand new plugs, started the engine and only let it idle, maybe ud get a good reading for fuel mixture at idle... but i doubt itd be accurate enough for u to make changes.

now that u do have the plugs out... how are they? id stick one back in and crank the bike to c if the spark is strong. is the electrode worn? is the spark weak? i cant imagine they would be with under 5000miles, but u never know.

the only other problems i could imagine are throttle body sync and idle adjustment. ez to check and fix if uve got the right tools, and honestly, ure bike should be able to idle around 1000rpm if it were running correctly. u never want it to idle that low but it shouldnt stumble at 1100rpm as u already kno.

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Naked 93' F2...... RIP -- 04/12/07
04' 600RR Black - currently stuck between track and street usage
- Brembo Master, Sato's, & Ohlins out back

it will idle completely on its own it just sounds strange... maybe its just the way one of these sounds with a low idle like that... I'm not a whole lot experienced with working on i-4 cyl engines and motorcycles.

I am much more handy with a small or big block v8 :)

they make better use as anchors

 

aHAH!

did the seafoam change anything?

stock exhaust is back on, new plugs in and seaform through it. Still does it though not as bad. I think i can hear the dreaded rattle at 5,000~ RPMS in every gear now... d'ya think the CCT can cause these symtoms as well?

I just had the same problem with mine. Take the vacum line off going to the fuel pressure regulator and see if there is fuel in the vacum line. Also with the vacum line off turn the ignition on without starting and see if gas leaks from the regulator. If so the regulator is bad and sucking extra fuel into the intake. This fixed my f4i.

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Don't eat the dead one's