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How Many Blocks You Got?
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4 Posts
Discussion Starter · #1 ·
Hey every one. I am new to these forums, and this is my first post/thread. Im really hoping that a long time Fighter pro can offer some fresh insight/advice.

I have been through 5 bikes all of which with the exception of one have been Fighters. I just love the Fighter style and what it stands for.

I recently bought a custom fighter from a buddy. Now this friend knows about bikes, but only enough to build them and make them run ok. In short he is NOT a professional mechanic and far from experienced in the field.

The bike is a 99' cbr900r frame and engine with a 94' vfr750 swing arm. Custom welded sub frame and 05' cbr1000rr front end. The bike is great from a far but far from great. I do though, love her set up and she has lots of potential to ,with some $$$ and elbow grease, be a beautiful and agressive one of a kind fighter.

Aside from a high RPM bogging issue that she first presented to me last night (which i have yet to look into and im hoping its something minor and/or an easy and cheap fix, like plugs or something) the bike has this air box/breathing issue which from what im told and have read is sort of common among a select few bikes once they are fightered out.

From what ive gathered this bike does not run right unless it can breath in rather stagnant air.. as opposed to direct ram air.. or something like that. We have done that airbox mod where we close up the two holes in the front of the box where the boots would have gone then drilled some holes into the back side of the box. Once this was done it improved the bogging issue a LOT! but... always a but heh..but, it is still not running the way it is supposed to. We tried a load of different amounts of holes to try and dial it in just right. No combination/placment of holes seems to make it breath 100% proper.

When i roll on the throttle she runs pefect, but when i grab a handful once it hits a certain rpm (not sure where with out guages, but if i had to guess id say prob between 4-7k) it totally dies out... then WAM, it will open up. it feels as if it had a turbo booster or something.

The carbs are squeeky clean and It has a satge 3 jetkit which he claims to have tuned. Can any one who may have dealt with this before or who may happen to have some fresh ideas shed some light of this for me? I have been riding like this for weeks now, and just learned to deal. Adjusting the way i ride to avoid having to feel the problem. But im totally OCD and i really just want her to run 100% because im going to begin working on all her cosmetics pretty soon but want the engine to be purring as it should before i go dumping off all my paychecks into cleaning and tightning her up.

I would like to thank any and every one who may reply to this and try to help me in advance, and say that im happy to have joined your community and look forward to getting to know all of you :)


PS; I also would like some ideas about what this new high RPM bog and sputter issue may be, but i will begin a new thread for this as not to jumble up this one with more than one issue at a time. So any one that may be able to give some ideas/advice about that please stop into that thread once ive posted. Thank you again every one!
 

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The friendly Ghost.
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13,174 Posts
(I am no expert just bringing up information others might ask for, useful to have on hand.)

You mentioned the modified airbox, what exhaust are you running?

What positions are your needles set at in the stage 3 jet kit?

Is the stage 3 necessary for the modifications performed? (Might flow too much fuel, see next question.)

What color are you plugs when you kill the ignition at bogging RPM? (Full load pull until bogging occurs and simultaneous kill switch and clutch lever, coast to a stop and pull the plugs to see what they look like.)
 

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How Many Blocks You Got?
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4 Posts
Discussion Starter · #3 ·
(I am no expert just bringing up information others might ask for, useful to have on hand.)

You mentioned the modified airbox, what exhaust are you running?

What positions are your needles set at in the stage 3 jet kit?

Is the stage 3 necessary for the modifications performed? (Might flow too much fuel, see next question.)

What color are you plugs when you kill the ignition at bogging RPM? (Full load pull until bogging occurs and simultaneous kill switch and clutch lever, coast to a stop and pull the plugs to see what they look like.)

Hey man, thanks for the reply and input..

Im running a full Erion system. It is also chopped to about 6" long, if that matters.. Idk what the positioning of the needles are, as i did not do them myself, nor have i adjusted them myself at all.

I did not even pull the plugs yet and did not know about this killing it , coasting and checking them thing before your mention of it now. I will be sure to do so at work on monday. I dont have many tools of my own, not the right ones any how. My trade for many years was finished carpentry in which none of the tools needed for this line of work are used.

I work at a bike shop as an apprentice and I have only began to learn to work on bikes about a year go and have not yet learned more than basic stuff.
 

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old fart
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3,794 Posts
I have just had similar on my CBR900RR engined bike! it would bog down between 5k and 7k RPM when given a good twist of the throttle, but it would drive through if ridden smoothly through that area.
i dropped the needles by two groves and it has all but lost the stumble and now pulls cleanly all through the rev range.
still need to get it on the Dyno though, to give it a final fueling run to be on the safe side.
 

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How Many Blocks You Got?
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4 Posts
Discussion Starter · #5 ·
I have just had similar on my CBR900RR engined bike! it would bog down between 5k and 7k RPM when given a good twist of the throttle, but it would drive through if ridden smoothly through that area.
i dropped the needles by two groves and it has all but lost the stumble and now pulls cleanly all through the rev range.
still need to get it on the Dyno though, to give it a final fueling run to be on the safe side.


Thanks for the reply man!

Is your also jetted stage 3?
 

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How Many Blocks You Got?
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4 Posts
Discussion Starter · #6 ·
I have just had similar on my CBR900RR engined bike! it would bog down between 5k and 7k RPM when given a good twist of the throttle, but it would drive through if ridden smoothly through that area.
i dropped the needles by two groves and it has all but lost the stumble and now pulls cleanly all through the rev range.
still need to get it on the Dyno though, to give it a final fueling run to be on the safe side.
Forgot to ask, did you also do the air box mod like i did?
 

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Registered
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740 Posts
Deleting ram air from bikes designed for it can be tricky. Have the pressure feeds to the bowls been removed? If still hooked up to a modified airbox, it can cause all sorts of bizarre running issues.

But a midrange bogging is likely the needles. If it's better if you romp on the throttle, it's probably too rich since more throttle lets more air in, but at a cruise/light throttle it's too rich. I would agree with the suggestion to try dropping the needles 1 clip (move the clip one groove toward the flat end) and see if it improves.
 
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