Hello all,

I recently bought a 99 900rr that doesn't run quite right. The bike has 7000 miles, and appears to be in pretty good shape mechanically. All stock except for slip-on an k and n filter. My bike starts, idles, and revs to around 5000 rpm perfectly but won't rev any higher unless you are giving it 1/8 throttle or less. Try to give it anything more, and it stutters and misses and won't rev out. Hot or cold motor, doesn't matter, it acts exactly the same. It runs extremely smoothly up to 5000 rpm, no miss, no stutter, no hesitation of any kind. I am a car mechanic by trade, so I know my way around stuff pretty well, and have had and worked on multiple bikes, though I am by no means an expert I initially thought carb problem, p.o. said bike ran great last fall, ran like crap this spring and he didn't want to mess with it.

Here's what I have checked so far-
Carbs completely dismantled and cleaned, diapragms checked, everything looks great. Stock 120 jets on all 4. Intake boots are not cracked, airbox is sealed down correctly. When the bike is running, all 4 slides flutter up and down evenly with each other. Tps sensor checked, voltage swings from 0-5 on the signal wire as you open the throttle.

Petcock dismanteled, screen cleaned, put vacuum on it and checked flow, all is good there. Also put brand new tank of premium in it.

Ignition coil grounds cleaned, voltage checked at coil, all 4 plugs are sparking, (although it is a weak spark compared to a car, kindof orange, not blue like a car usually has.) Problem maybe?

Bike's voltage checked while running, charging at all rpms.

Tried running air filterless, and also with stock muffler, both made no difference. k and n messing me up maybe?

At this point I decided to dig a little deeper so I -

Pulled valve cover, checked cam timing to make sure I hadn't jumped a tooth, all is good there. Checked tdc versus crank trigger to make sure it hadn't spun at all on the crank.

Did a leakdown test, all cylinders are between 2-4%, which is really good, so no broken springs, bad rings, blown head gasket, etc.

Bike does not smoke, tick, gives no signs something is wrong until 5000ish.

I am quickly running out of ideas and am hoping the gurus on here can help!

Thanks in advance for your help,

Ben

 

Maybe it's a fueling problem?

fuel pump, make sure everything is working properly?

 

My 99 doesn't have a fuel pump, it's just gravity feed. I keep coming back to a fuel delivery problem of some sort but I don't know for sure. I feel like I've double and triple checked everything I can think of. I did dig a little deeper today into it and noticed the fresh plugs I put in a couple of days ago already already look fuel fouled. I don't know how thats possible with stock jets in the carb and a k and n filter, if anything I think it would be lean, not rich. Kinda makes me think weak ignition not burning the mixture maybe? I don't know I'm so fed up with this darn thing right now- I'm way to stubborn to take it to a shop though- I keep hoping I'll figure something out soon, although on a positive note I am getting really good at taking the fuel tank/airbox/carbs off

Ben

 

Hopefully someone with more knowledge (much more than me lol) can chime in.

Fouled plugs are a sign for sure.

 

Thanks for the replys mt wallet, I certainly wasn't implying you didn't know what you were talking about with the fuel pump, I reread my post and realized it kindof came across that way. I checked key on voltage at the coil and it's about a volt lower than the battery so I'm thinking maybe the voltage drop somewhere in that circuit is giving me a weak spark? I'm gonna keep tinkering and hoping someone on here has the answer before I push the bike off a cliff

Thanks,

Ben

 

Hi there....
Sounds like under load its breaking down ? MAybe the spark issue is an issue? Have you tried replacing the plugs anyway (often the most overlooked because they rarely give problem nowadays)
Did you say it will rev beyond 5k if coaxed by a slither of throttle?
If it does i'd say its electrical IF its getting enough fuel ? Is the vacum
pipe become Blocked?
What about the engine breather pipe? If this gets blocked it can physical lock the motor up?
The carb model is very straight forward really not alot to go wrong and does sound like its all in good condition.
Anything else strange ?? Like needing NO choke to fire up OR lots of throttle ?? will it idle nicely .... and you say its fine upto 5k but is that on the stand or actually pulling you along under some load?

Let us know !!

 

Sorry ... just re-read the whole thing again , you had replaced the plugs!

 

Thanks for the reply, it will rev beyond 5 with just a slither of throttle, but anymore and it starts to miss pretty bad. Starts with no throttle on choke, take choke off after 15 seconds, idles and sounds great. It will rev past 5 with no load but not under a load. As far as fuel flow I put a new vacuum line on to petcock and it appears to flow plenty good. I have pretty much nailed it down to a coil problem, I cleaned all grounds on the motor and it runs better but still the same problem. I don't know how both coils can go bad just sitting, but stranger things have happened I suppose. Let me know what direction you think I should go next or if I should order some coils off ebay for $30 and see if that fixes it.

Thanks
Ben

 

Unlikely that BOTH coils would go at once and cause the same problem... more probable is the ignitor .. the more i think about it i'm convinced its fuel starvation .... Take the tank off air box and remove the fuel filter ... if poss set up a small container on a stand with a pipe to attach to the fuel splitter. Using a clear tube you can see fuel being drawn into the carbs.
This is what i use ....its an expansion tank .. but a funnel will do







The filter can cause problems ... remove it so you have a direct path into the carbs .. if it seems fine test it with the tank on but bypassing the filter ..

Hope this helps .. keep us posted

 

Thanks for the reply! I tried a different set of coils, same problem. I put a timing light on it with both sets of coils, and i'm intermittently losing spark at higher rpms. Is it possible for the pulse generator to fail only at higher rpms? Thats kindof the way I'm leaning, although I will try your fuel trick and see if that works.

Thanks,

Ben