'91 CBR1000F won't rev out

[Speedracer]

Got a nice CBR1000F that I've had for a while. No issues, 25000 miles (40k) on the clock. Fantastic tourer, great fun on track days.
But now it's acting strange

Was coming back from christchurch and noticed it wouldn't rev to the redline.
And it's gone downhill fast from there, within a week of little riding doesn't like to rev past 7-8000 but will rev out further to the redline in a couple of seconds (in neutral).
In gear it is like hitting a rev limiter, feels grunty down low like it should but then hits a wall. As in it won't go past the new rev limit while in gear, only in neutral.
Idles ok.

UPDATE:
Thanks for all your suggestions and help!
Still not fixed but it revs out slightly quicker to the red line - will go to the red line in 1st while driving, just very slowly in the 8-10k flat spot. (in neutral it is fairly quick but has much less pickup)
While in the flat spot it sounds like a bike running out of fuel, but then when it hits 10krpm or so it can take off which seems counterintuitive to me if it was running out of fuel in the float bowls?

UPDATE2:
Seems to go now, either my last ditch effort extreme carb cleanout worked or what is more likely it was a dirty electrical connector I missed earlier. (the connector between the ignition coils and the main wiring loom). Thanks again for all your help :niceone:

Summary of what I've done so far:
Air/fuel
*** Cleaned carb with compressed air (and brakekleen and CRC clean-r-carb), thoroughly.
*Cleaned carb float bowl out, removed and checked jets (everything was very clean)
*Carb Vaccuum Diapgrahm
**Removed diaphragms, tried various things (CRC, autosol, sucking clean-r-carb through the vacuum holes which seem to have plenty of vacuum)
**Diaphragms seem to go up and down as you'd expect, can't find rips or tears anywhere i.e. they don't drop down instantly and they do go up under load
**after spraying CRC in the top of the vacuum diaphragm the bike ran perfectly (once) through the rev range which is the only time it has since the problem occurred.
*Removed air filter and reinstalled with sealant (runs worse without air filter, no difference noticed with sealant) Air filter looks fine.
*Drove bike with the choke on, runs marginally better (not a huge difference)
Fuel
*Ran carbs through a funnel bypassing the fuel tank (can't see a filter anywhere unless it's built into the fuel tap)
*Drove bike with the fuel cap open (to check breather)

Electric
*** Found connector from ignition coils was a little dirty. Seems to have fixed it.
* Checked pulse generator and ECU output with oscilloscope.
*Replaced spark plugs which looked fine before I replaced them (light brown coating on porcelain/tip with black ring)
*Tried spark plugs out with bike running at idle (nice strong sparks, nothing intermittent)
*Checked coil resistances and timing unit resistanced (all within spec)
*Checked connectors around the bike (found one corroded terminal on the ECU that only goes to the tacho presumably to indicate RPM)
*Disconnected one ignition coil temporarily (bike just runs half as quickly through the flat spot)
*Found the regulator. It tests ok with the diode check on my multimeter (I am not 100% sure how to test it), but looks dodgy. Cleaned the connector block.

Other
*Tappet clearances
*Noticed valve timing was correct when doing tappet clearances.

[hayd3n]

you say air fliter looks fine but have you tried a run without it???
if its better then youll know the problem

[Rhys]

Fuel filter ?

[ducatilover]

Try the fuel filter
Double check for ripped/holed slides
Air leaks
Fuel pump (if it has one)

If it stops dead at the same revs in every gear though, properly dead and won't climb, it may have a factory speed limiter that's playing up

[James Deuce]

Reg/rec, stator, battery.

[Speedracer]

Fuel filter ?

I warmed it up slightly then filled the carb all the way up with fuel using a funnel direct on the fuel hose - no filters in the way that I can see. Then started and revved it straight away. Same problem. I tried the choke on and off and it seemed like it revved slightly higher with the choke on (order of another 1000 rpm).

Even if there was a blockage, my theory is that if I rev it straight away from full float bowls I would have thought that would fix it temporarily if it was a fuelling problem?

[FJRider]

*None of my sockets fit the spark plugs like they're 17mm but not really i.e. 18mm so I haven't looked at them but I can't imagine they are the problem?

*Air filter looks fine.


I guess it's pointing to an air leak that I can't find or a faulty diapragm...
Tips?

How long since the plugs were changed ??? A bit of crap in the fuel picked up from a gas station may have gummed the plugs up. (and plugs wont last forever)

Plugs first. Check gaps/CLEAN ... replace them with new even.

Air filter CLEANED.

Eliminate issues ... not just dismiss them.

One "fix" at a time. Otherwise you wont know for sure what the problem was ... (if the problem is cured)

[FJRider]

I warmed it up slightly then filled the carb all the way up with fuel using a funnel direct on the fuel hose - no filters in the way that I can see. Then started and revved it straight away. Same problem. I tried the choke on and off and it seemed like it revved slightly higher with the choke on (order of another 1000 rpm).

Even if there was a blockage, my theory is that if I rev it straight away from full float bowls I would have thought that would fix it temporarily if it was a fuelling problem?

Try to repeat the choke thing on the road at speed.

Full float bowls don't last long without resupply. If the issue isn't fuel ... it could be air or spark problems.

[James Deuce]

It's a Honda. First thing to check is the Reg/Rec.

[Speedracer]

Looks like it was those vacuum slides
They looked dirty underneath and I cleaned them out with clean-r-carb.
Not sure if it's 100% fixed but there's a huge difference right there.

Any ideas what would cause this?

[ducatilover]

Old age.
Polish the slides and slide bores (carefully, liquid autosol works for the bores, with cotton buds)

[Speedracer]

Old age.
Polish the slides and slide bores (carefully, liquid autosol works for the bores, with cotton buds)

Hmmm it seems the problem is not permanently fixed - But if I forceably blow in the diaphram breather it revs out again.
Too much blowby on the slides perhaps?!

Where do I find this magical autosol? or is it carb slide replacement time
What is so special about autosol, wouldn't engine oil or CRC work?

[ducatilover]

Aren't the diaphragm breathers on above the inlet, not in a pipe?
There should be a carb bowl breather hose coming out over the top of the carbs, but I don't think the diaphragms have a breather, as such

Diaphragms needing more pressure will be, leak at top where the diaphragm seats, split/holed or the holes are drilled out way too big. Or your engine pulls no vacuum whatsoever

Autosol is just metal/alloy polish, buy it from Repco/gas station/Mitre10.

[sugilite]

I noticed #4 is a bit bouncier (it's easy to see)
If it is still doing this, that is my pick of what your problem is.

[mouldy]

Put some new plugs in it , not revving out is a sympton of plug deteriation

[Speedracer]

Put some new plugs in it , not revving out is a sympton of plug deteriation

Plugs look fine-
Black ring, inner is light brown all over including porcelain and tip. Sparks fine, sparks a long way to the head if you let it. Gaps are consistent.

[Speedracer]

Old age.
Polish the slides and slide bores (carefully, liquid autosol works for the bores, with cotton buds)

Hasn't seemed to improve it in my case unfortunately :-(
I tried adding CRC to the mix and it made no difference.

Thanks for the tip though.

[Speedracer]

you say air fliter looks fine but have you tried a run without it???
if its better then youll know the problem

Seemed worse without it unfortunately.
EDIT Tried also re-sealing the air intake seal and remounting the filter in case it was not installed right and if it made a difference it was not much.

[Speedracer]

Seems to be acting a bit randomly

After taking the slides out I blocked the breather pipe and it stopped sucking in a lot of air. Then it would rev to 10k and then suddenly release full power to the redline. But I couldn't see any difference internally when I took out the slides again.
After Autosol + CRC on the slides it didn't do anything different, and then one time revving it up from 6k in 1st it kicked in at 9krpm to the redline but I couldn't repeat it.

Its like an intermittent fault. For example on the last test ride after CRCing the top of the slides (vacuum part) (and a few revs in the garage) it took off and went all the way through the rev range properly once I got to a 100k area. And then it wouldn't do it again.

Thanks for all your ideas guys.

[AllanB]

Check the fuel tank cap breather it not restricted. If unsure crack the cap open slightly, duck tape it in place (ie it is just slightly open not sealed shut) so it will not fly open and spray you with fuel.

Go for a ride and see if it it revs out cleanly. If it does, remove tape, shut cap and try again. If it does not rev then the breather is blocked.

[hayd3n]

Seemed worse without it unfortunately.

another thing
have you checked for carb boot leaks? quick test spray water on the carb boots when running and youll soon know if its leaking

[FJRider]

Plugs look fine-
Black ring, inner is light brown all over including porcelain and tip. Sparks fine, sparks a long way to the head if you let it. Gaps are consistent.

I've seen that written in a few threads, but tried new anyway. Sometimes ... it was the problem.

Eliminate not dismiss problems.

[Speedracer]

another thing
have you checked for carb boot leaks? quick test spray water on the carb boots when running and youll soon know if its leaking

Thanks for the tip, I hadn't heard of using water spray. I did try a gas torch (not lit) and a thorough visual inspection. I heard some obvious leaks before and fixed them (loose boots which must have been loose for quite some time) and it made no difference. Other than that I haven't found anything in this area yet.

EDIT tried the water spray and nothing - no leaks I can find.

[ducatilover]

So does power go flat and taper off, or is it stopping dead at those revs?

If it's stopping dead and not climbing at all, apart from random full power bursts, it sounds like a speed limiter fault and at the revs you state, that's where it'd be doing 180km/h on factory gearing, which is usually where a speed restirctor will limit RPM when there's no resistance or a short in the circuit

What I would do, after plugs and checking the fuel pump, plus relay, is pull the speedo out and look if there's a unit with three wires in the speedo itself.
if there is, check connections from that, to the CDI unit, take a note of what colours they are
If you have one unusual common colour (usually pink, I think) earth it from the CDI to the frame with a resistor in there, I have a random 12v LED that seemed to work a treat on a Kawasaki system. I was having the same issues, was a prick of a thing

[Speedracer]

Check the fuel tank cap breather it not restricted. If unsure crack the cap open slightly, duck tape it in place (ie it is just slightly open not sealed shut) so it will not fly open and spray you with fuel.

Go for a ride and see if it it revs out cleanly. If it does, remove tape, shut cap and try again. If it does not rev then the breather is blocked.

Didn't work. Thanks for the tip though.

[Speedracer]

So does power go flat and taper off, or is it stopping dead at those revs?

If it's stopping dead and not climbing at all, apart from random full power bursts, it sounds like a speed limiter fault and at the revs you state, that's where it'd be doing 180km/h on factory gearing, which is usually where a speed restirctor will limit RPM when there's no resistance or a short in the circuit

What I would do, after plugs and checking the fuel pump, plus relay, is pull the speedo out and look if there's a unit with three wires in the speedo itself.
if there is, check connections from that, to the CDI unit, take a note of what colours they are
If you have one unusual common colour (usually pink, I think) earth it from the CDI to the frame with a resistor in there, I have a random 12v LED that seemed to work a treat on a Kawasaki system. I was having the same issues, was a prick of a thing

Interesting idea... It's not stopping dead though and the speedo goes up to 280k or so, so I don't think it was the limited edition.
I tried manually disabling one coil (2/4 cylinders) it just climbs half as fast (if you could call it fast) through the flat spot (still climbs).
Also tried CRCing and wiggling connectors but I didn't find any obvious problems and no difference was made so far. I'll look through the wiring diagram in the manual though... there is no speed limiting wire in the wiring diagram.
Thanks for the tip.

[FJRider]

When I first bought My FJ ... it had similar issues. It had been imported from Japan. Carbs were cleaned and the tank lined. It had an inline fuel filter that looked ok.
While attempting a 1000 mile rally (I completed it before the allowed finish time) ... top end power/speed was limited. On completion I removed said inline filter and cut it in half. It was VERY blocked ... to the extent I was surprised fuel actually flowed.
New filter ... issue fixed.

[HenryDorsetCase]

Seems to be acting a bit randomly

After taking the slid


es out I blocked the breather pipe and it stopped sucking in a lot of air. Then it would rev to 10k and then suddenly release full power to the redline. But I couldn't see any difference internally when I took out the slides again.
After Autosol + CRC on the slides it didn't do anything different, and then one time revving it up from 6k in 1st it kicked in at 9krpm to the redline but I couldn't repeat it.

Its like an intermittent fault. For example on the last test ride after CRCing the top of the slides (vacuum part) (and a few revs in the garage) it took off and went all the way through the rev range properly once I got to a 100k area. And then it wouldn't do it again.

Thanks for all your ideas guys.holy shit that sounds exactly how my VFR400 is running

[Speedracer]

I've seen that written in a few threads, but tried new anyway. Sometimes ... it was the problem.

Eliminate not dismiss problems.

OK I've given it a go... Plugs replaced.
Unfortunately this has not fixed it.
I've updated the first post with a summary.

Thanks for all your help.

[FruitLooPs]

http://www.gixxer.com/forums/showthread.php?t=106093

Sounds like the same issue, pitty it wasn't resolved. I had intermittent running on one cylinder on my bike, coils tested ok with meter cleaned carbs checked HT leads were in spec etc. I had tested the leads without the plug boots attached, which were NGK resistor models 5K ohm I discovered the bad cylinders one wouldn't give me a reading at all, swapped it out and away we went. :niceone:

You've gone over pretty close to everything it could be, keep at it.

Also CDI's can get leaky capacitors that can cause all sorts of worries, I've read of some guys pulling them apart and replacing bits (unfortunately the PCB is usually filled with a horrible foam/plastic goo to insulate it from everything)

[Bikemad]

i had the same sort of problem years ago with an old 750F............chokes were set wrong so they were half on all the time

[Speedracer]

Long story short it seems it was an electrical fault. But in case it wasn't this is what I did before it started working.

I borrowed a compressor and blew the carbs out to the max. They are very clean. Found one of the vacuum equaliser? hoses (goes between 1-4 and another from 2-3 on the engine side) had a hole so replaced both.
I also took care to clean not just the main jet, but the tube the needle goes up and down in with a few sprays and air as it looked not perfectly clean (I couldn't really fault it though).
Disconnected the carbs and fuel pisses out very fast all the way to the carb like it should.
.....Hooked everything up but no go.

So in preparation for this possibility I had also borrowed an oscilloscope. And as soon as I attached it the bike worked. :weird:
All traces looked great, no misses. So I put the seat on, drove it and it revved up 3 times ok... and then not again. :Pokey:

But the bike now had an obvious occasional miss at lower revs, running marginally rougher than normal so I was thinking it was an electrical issue. At the ECU all measurements were in spec and traced ok at one point, so there had to be a dodgy connection somewhere.

Wiggled the crap out of the ignitiion coil connections (primary side) which I've done before and then found another related connector which plugs the ignition coils into the main wiring loom to the left of the ignition coils. This looked dirty so I cleaned it.

As soon as I did that the bike revved ok again. Drove it for a few minutes and it keeps working.:niceone:
I wouldn't have picked a dodgy connector causing a flat spot but that seems to be what it was

Thanks for all your help! :2thumbsup

[frogfeaturesFZR]

Good work. Bet you were thanking every god you could think of !