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Thread: '91 CBR1000F won't rev out

  1. #1
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    '91 CBR1000F won't rev out

    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

    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.

  2. #2
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    you say air fliter looks fine but have you tried a run without it???
    if its better then youll know the problem

    plastic fabricator/welder here if you need a hand ! will work for beer/bourbon/booze

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  3. #3
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    Fuel filter ?

  4. #4
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    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
    Quote Originally Posted by Paul in NZ View Post
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    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




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    Reg/rec, stator, battery.
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  6. #6
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    Quote Originally Posted by Rhys View Post
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    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?

  7. #7
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    Quote Originally Posted by Speedracer View Post
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    *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)
    Bravery is not being without fear ... but continuing ... in spite if it ..

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    Quote Originally Posted by Speedracer View Post
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    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.
    Bravery is not being without fear ... but continuing ... in spite if it ..

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    It's a Honda. First thing to check is the Reg/Rec.
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  10. #10
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    Update

    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?

  11. #11
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    Old age.
    Polish the slides and slide bores (carefully, liquid autosol works for the bores, with cotton buds)
    Quote Originally Posted by Paul in NZ View Post
    This quote is hidden because you are ignoring this member. Show Quote
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
    Bling your bike out!
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  12. #12
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    Quote Originally Posted by ducatilover View Post
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    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?

  13. #13
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    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.
    Quote Originally Posted by Paul in NZ View Post
    This quote is hidden because you are ignoring this member. Show Quote
    Ha...Thats true but life is full horrible choices sometimes Merv. Then sometimes just plain stuff happens... and then some more stuff happens.....




    Alloy, stainless and Ti polishing.
    Bling your bike out!
    PM me

  14. #14
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    Quote Originally Posted by Speedracer View Post
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    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.

  15. #15
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    Put some new plugs in it , not revving out is a sympton of plug deteriation

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