Hi there fellow enthausiasts

The name is Erwin, all the way from Holland. I have tried several Dutch forums for this problems, all advice's have been tried and still....

The problem is when i first bought it (like most first time racer buyers) i didn't have the guts to push the throttle all the way, so I bought it in good faith.

Afterwards after getting used to the power, i noticed a stutter at 10.000 rpm.

Sofar i have changed the rectifier (exploded), CDI (thats Dutch probably but I mean the ignition mapping unit) becuase it started to heat up (i think its damage because of the exploded rectifier), changed the exhaust to the original one, i cleaned the carbs, cleaned the original airfilter (which still is a bit dirty), new sparkplugs, new.....a....the thing that makes the feul pump going,

also new tyres, and chain/sprockets, oil and filter, but that was just maintanance.

So i tried a few things allready, the bike runs perfectly, it starts perfectly, it pulls good torq.....only when it reaches the 10.000 rpm range the stuttering starts.

I noticed somebody haveing the same problem here in 2010, did he ever got to fix it?

I am kind of frustrated here, tried a lot and starting to have no clue what to do next?


Can anyone help me?

 

I'm not sure you want to push a 900 over 10000.

 

Most I've push my 900 to is 9rpm...that's already pushing it . Bike don't even need 9 to lift a wheelie... If sputtering??? Either carb is not getting gas fast enough or short of air??? Unbalance amount of air, gas & ignition in chamber will cause sputtering. Short of gas or air will result is sputtering. Since you've already clean to air filter? Why not get a new one (K&N) . How about your gas filter? Can it be dirty that gas is not flowing fast enough when push to 10rpm? How about carb? Have you sevice/clean carb? Have carb been jetted/ adjusted?

Good luck...& let us know...

 

My SC-28 starts red at 11.000 and the rev limiter should kick in at 13.000 and the end is 14.000 rev's

Its a Europian bike as I am a Dutchy A colleague of mine has the same, from 94 and his just fly's too the red zone. Today i removed the plugs and saw that the first was a bit white. I think maybe I need to adjust the floaters. Indeed I have a feeling it starve's on gas.

Filter in line was clean btw, and i had revised the fuel pump so the flow is good. The ignition unit change also resulted in a cold seat (which got hot before i swapped that!). So funny enough everything i do turns out in a good result and change in performance, only it did never tackle the high rev stutter. The thing is when i got used to the blade the sporty guy in me came alive and now its just plain annoyance when you feel the stutter coming at 9.500 rev's. I could decide to just leave it and not pull over 9000....but with the idea in my head knowing it will not go over it in a good clean manor i really want to fix this.

Bare in mind that working on the bike after i bought it a lot of things came to light which tells me the first owner NEVER maintained it (and people tend to think that a first owner buy is the best buy!). It has 37000 Kilometers on the clock (I reckon thats 20.000 miles) and even the original chain and sprocket with which it had left the factory where still on the bike (and in a state that you would not want to drive it with!)

I was afraid i would not get a 100% answer like : yeah its really simple, just to "this" and your fin; as its a problem not many blade drivers have seen. Its another lesson that it is very important to keep any bike maintained....problems just add up, and the next buyer has to puzzle out what the h*ll is wrong with their newly bought toy.

Guess there is no other alternative to tear it apart, refurbish, and put it back together again. And that is a bit sour as i really thought (caus it is running really nice beside this little high rev stutter) i had bought a second hand dream.

Thanks for the reply's sofar!

Maybe a Dyno run could shed some light to the problem....

 

Hi guys

Update from my side: Cleaned the carbs thouroughly and replaced all pilot screw sets as one had corrosion on it.

As I expected it made totally no difference.

The only thing i can test and replace are the thingy's wired to the spark-plugs, the rest is allready been replaced....I am totally out of options.

One thing left and thats measuring the valve clearance....but could tight valve's result in high rev stutters?

If anyone recognize's this problem. please do not hesitate to throw in your 2 cents, it could really help me out as i am stuck, I almost changed every part concerning sparks and obviously there is nothing wrong with the feul flow.

 

white plugs mean you are running too lean. Take the bike to a dyno and see where you need to change the air/fuel. At 10,000 rpm I would imagine you need bigger mains.

 

That could be an option, but i still think there is something else. maybe a weak fuel pump, caus it doesn't do nything weird untill you push the throttle hard a few times. It also gets a bit worse with longer periods of fast speeds, then when i let it idle for a while and then push the throttle the revs go up to 12.000 easy, when i then go back in gear and try to rev up to 12.00 with the load of the bike the stutter appears again. It's like the bowels don't fill up quickly enough when pushing the bike.

Does anyone here perhaps know anything about the reliability of the cbr fuel pump itself? (not the contacts, i revised them already) I have been thinking about a fuel pump that is connected to the key-switch and only pumps when needed (pressure sensitive)

I mean, this is , imo, a big flaw of the cbr, a continue's pump that only keeps up one static flow, instead of adjusting itself to the needs of the bike at a certain point of use.

In the mean time i will check my valve's when i have the time, seeing what parts came off that i revised the bike has not seen maintenance in a long long while, and it never hurts to check on them.

 

What year is this?? I didn't think they had fuel pumps until the injected models came out. I could be wrong. My 98 doesn't have one. Gravity feed to the carbs.

 

Mine is '95, type SC28. And it does have a fiel pump yes, I revised the contacts on it. Its a continues pump (Why?!?!) that starts when the engine is running and stops when you kill the switch. It does not rev up, its just a simple continues pump that is sensitive to wearing out. I must say this is a true desing flaw and i can not get my head around the fact they didn't use a pressure sensitive example that only gives when the carbs need fuel. I mean, what is the use of a pump continuing its flow even when the bowels are filled to the max?

I got a pressure sensitive example of a friend om mine, from a FZR600, let's hope this will solve the issue...I'l update when i get it assambled

 

Hi Folks

Been a while, sorry for the lack of info on my part

First: My fuel pump IS a pressure sensitive example :-P Nothing wrong with it, works just fine



But i did some stuff in the mean time and I have shutted may things out of the problem. Last Saturday i went to the Dyno and we trashed it in 6th gear a few times, we swapped almost everything on the ignition part (from which it clearly seems to come) but nothing really came to light and we where left with just 2 options:

1: De cilinder-head. It could be a valve kind of sticks or that the valve springs have become weak overtime resulting in floatinf valve's at the higher rpm's

2: Pule generator. It could be that a faulghty pulse generator could be the issue as it is the ONLY thing we could not rule out on the small amount of time we had that day.

She still pulls 102,7 Bhp on the rear wheel, (with over 90 N.m torq) with a (too rich) mixture and the high rev stutter. The guy from the dyno thinks if we can rule out the faulght, give it another adjustment inlcuding a K&N filter and dyno kit he can pull out a 170Bhp in just under three hours of adjusting and testing.

Of course i first have to see if the pulse generator is the issue. So my MAIN question now is: does anybody here ever had a faulghty pulse generator, and what artifacts comes with that (high rev stutter, or a no-start or whatever, every comment counts!)

Here is a small avi of the run, you can see the bike shake at 10.000 rpm at the first 6th gear run at 1:56, also watch the screen on the 2nd try (at 2:30) and see the right-above clock/meter. That is the probe connected to the pulse wire going to the ignition control unit, and you can clearly see the clock dropping as probably the pulse's drop. Ignition unit has been swapped three times and that didnt give result showing there is a pulse faulght, but not in the coils and not in the control unit. So far we tested:

Coils: OK
CDI(igntion control unit): OK
Carbs: VERY OK, Nice clean and crisp, though mixture not totally perfect, synchro OK
Rectifier: Broken AGAIN, swapped it on site with a genuine part for once, now OK
Dynamo/Alternator: OK
Airfilter: OK

Not checked: Pulse genrator, motor mechanics like valve's and springs. Vavle clearance was perfect btw.

The RUN

Feedback if possible Woul;d be greatly appreciated....i am getting closer and closer and working hard to resolve the issue....