Hi guys. New to the forum, but really really could use some advice from the guys that know. I have recently purchased a CBR1000F '89 90' model. At first it was extremely lazy and low on power, since then i have completely redone the motor, upped the compression a bit, ported the inlets and out lets. It feel like a whole new bike. Starts and idles like a dream, revs beautifully and has heaps of power, but it cuts out at 6000/6500 rpm. Does any one have any idea why it is doing this. My first thought was it was starving, so we have upped the jets sizes, now I'm thinking its electric as it is a very abrupt cut out.

Please guys, any bit of advice will be greatly appreciated.

 

Welcome to the CBR Forum Daniel.

A couple of questions? Was it doing the 6/6.5K RPM drop before you rebuilt the motor? Is the airbox/filter standard? Did you refurbish the carbies at the same time you rebuilt the motor?

When you say sudden, is it 6000 down to zero or just bogs down seriously?

Cheers, SB

 

Thanks so much for the quick reply. To answer your questions, yeah we did completely refurbish the carbs and had them properly sinced. Air filter is standard yeah. To be honest, before we redone the motor it was so lazy, the revs took ages to climb and thus we never really paid to much attention to whether or not it was cutting out. Now how ever the revs fly up, and yeah, it doesnt cut out dead, but as you say, bogs down very harshly.

 

No problems Daniel - I'm up very early in Australia writing a report and the CBR Forum is a pleasant distraction while I think of the next section to write

OK, so it bogs down seriously. Does it miss firing on cylinders or just 'slow' down. I'm thinking if it misses, you might want to look at the coils/leads/caps. There is a nice stick coil mod you can do to overcome problems with 20 year old coils.

If not that and we are still chasing electrical, I'm not sure the rectifier/regulator would cause that - others may yet correct me - as I have little experience in that department. There is a fairly comprehensive test sheet that can be downloaded from the site to aid in identifying electrical problems. I'll have a look for that after a coffee and post the link.

Here's the link!

http://www.electrosport.com/media/pd...ng-diagram.pdf

Someone may yet respond who has had a similar problem and diagnosed the cause, but this is a start anyway.

Cheers, SB

 

Thanks again so much. I to suspected it to be electrical, so you have confirmed my suspicions in that area. I will go through the chart and see if i can diagnose the problem from there. Its hard to tell if its missing at all, its something I've never experienced before. I am in South Africa, so its quite late here already, but what I'll do is tomorrow take it out and try and record it and perhaps if i upload and sound clip or video it will help with the explanation.

 

No problem Daniel. One of the forum Administrator's, Shadow, a CBR1000F tragic like many of us, is from South Africa - east coast - so he may be able to help more as well.

Cheers, SB

 

G'day Daniel , welcome to the forum . as suggested by SB , stick coil mod may be a very worthwhile up grade . this will at least one area of weak link electrically . it sounds like fualty leads or coil to me . good luck .

 

I would check the petcock(fuel tap) to be sure it's delivering fuel at the correct rate - the filters inside sometimes get clogged and only show there's a problem when you crank the bike hard. It could also be the coils breaking down as has been mentioned by Naga.
You say the bike revs like a dream - so are you saying the problem only manifests itself when the bike is under load, ie running under power on the road, not just at idle in neutral ?
Give me a call on BBM if you need help from a "local" 26D81C49

 

When you put bigger jets in did you shim (washers) the needles ?
When I did my 93 I had to take the shims back out as it was dumping
too much fuel in and bogging down at 6k Also make sure your intakes
from carb to motor are super tight no air leaks.

Since you worked on the carbs - imo - that's where your issue lies

You could also try the old jets and add two shims (washers) per carb

Since you rejetted, I take it there was a reason, such as new high flow
exhausts added ? if you went bigger jets on a stock exhaust it's running
way too rich and bogging down

my 2 cents BTDT

 

^ Sounds like it runs great until sudden bog down. As described its not a slow bog. Different than jet problem I think.
I know what your saying but sudden bog is more like fuel or air feed. Could be jets however but.....

Two things that we have seen are;

(1) vacuum locked tank
What happens if the tank fill cap is open when ridding?

(2) "h" shaped divider missing from air inlet and rubber intake collapses at around 6k rpm.

Doesn't sound electrical to me.