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Bike not revving past 6000rpm

Discussion in 'Technical and Troubleshooting Torque' started by tmg, Jun 3, 2007.

  1. since I've been riding, I've had a few issues pop up with my bike performance.

    first, it was the coils stuffing up when it rained, and the bike pretty much ran on 2 pistons instead of 4. Now that I have replaced the faulty coil with one from my stash of CB spares, it runs great, except when it gets to about 6000rpm...it just won't go any furthur!'

    I give it stick slowly, but all that happens is popping and it makes the bike convulse almost, like their's a rev limiter kicking in or something.

    It could be anything really - timing, air/fuel ratio, stuffed secondary jets in the carbies, a whole myriad of problems, even the coils could still be stuffing up, I don't know.

    I would just like to able to go all the way around the Rev Dial to 9500rpm and be able to do it without the bike feeling like it has to try to get their. Is there some way I can rectify this problem? My housemate that is now back on two wheels and has been riding for about 20 years, suggested getting a set of race carbies for it.

    I would like to keep my bike a bit longer myself, but if I can't get this problem out of the way, I think I may have to get something newer, lighter, and faster.... I just want to fly.
  2. You have answered your own questions.

    Start testing the items you listed. How is the timing shain? does it idle smoothy?

    I suspect your stash of used coils may well be no better than the ones you replaced..., how about the leads? Are they old and or split and arcing out anywhere???
  3. it really does need a full on tune and service, then I will see how it is, but I would love to order a new pair of ignition coils myself - high performance ones, then I will KNOW that spark won't be a problem.

    Also the idle is pretty sporatic (spelling), it's all over the place and when it's warm it idles at about 1500rpm, which IMO seems a bit high. it goes ok between 3500 and 5000 rpm, but before and after that rev range, performance is mediocre.

    Also at around 3000rpm, the tapets are very noisy and tick heaps, which means the valve shims need adjusting.
  4. got the bike back from the bike shop on friday last week, they said it was the C.D.I units, or spark units. so I used my stash of parts and dug out the spark units from there and swapped and changed till it idled smooth, and then went riding.

    It went awesome! but today and yesterday - 12th and 13th, it has screwed up big time. it is idling worse than it ever has, and when the engine is under load it pops and bangs and really lacks power.

    Maybe I should just check the timing chain tension today to see if that could be the problem, I got the manual so it won't be hard to do.

    Another thing is I rang around the bike shops, a while ago for new front brakes = $575 a piece, and today (13th) for new spark units = $400 a peice. Man it seems having a peice of history is expensive to maintain. Starting to get over it.
  5. OK, my guess is you either have a plug cap that is cactus or your should have R type plugs.

    This lack of resistance has caused the coil and/or CDI failure.

    Don't always trust the NGK cataloque.

    The plugs listed for my bike don't work because they are not r type.
  6. In my workshop manual it says that the type of spark plugs fitted to my bike are the NGK plugs. I don't know if they're the problem, but I would like it to be fixed. Another thing I found today was that when I went to check the timing that after I took the igniter/dizzy cover off, a heap of oil spilled out......I am sure that this isn't what is meant to be happening......can someone tell me cause it seems that after a good run, everything is collapsing in a nice big gooey pile of shit.
  7. Hmm oil is not good or normal, sounds like the seal has got old and perished and with the extra pressures of a good run has let go.
    Is an easy fix but fidley, I'll have a look see if I can find the manual for my old CB900F2B, was the same motor as yours just had a longer stroke.
  8. OK then check the caps. My ignition runs in the oil cavity, but yours might not.
  9. the noisey valves probly means the valves need adjusting, im not sure if CB900's used tappets or shims, i had a late 80's CBR1000 that used tappets which would lead me to beleive that a CB900 might use tappets aswel, but im just guessing. If your good at DIY then tappets can be done yourself with the right tools, but if its shims then you really need to get a mechanic to do it. My CBR1000 had really noisey valve train and it turned out to be a worn cam-chain and tensioner.

    The running rough could be the carbies or the spark, id b using the manual and checking the resistance values of your coils, leads, and caps to see if they are ok. The CDI is the only part of the electrical system that you cant really check so you've sorta gotta eliminate everything else, or replace it with a known good one. I dont know about the R plugs, ive interchanged R and non R plugs on lots of old things with absolutly no problems, and from what ive been told by mechanics the R only really matters in newer bikes with stuff like coil + cap.
    If they are all ok then id be taking off the carbies and either pulling them apart and cleaning them myself, or taking them to a mechanic to clean and check out. I had an old GSX1100 suzuki a while back that had holes in the vacuum slide diaphrams that had the same problem of running up to about 6000rpm and then running out of steam, the vacuum slides just werent opening enough. Although if this is the problem it wont be easy finding replacement good ones...trust me.

    Its amazing what you can learn by owning old bikes that never work, and not having any money to get them fixed :)

    Hope this helps
  10. just had another thought, it could also be an inlet manifold leak. with the bike idleing spray around all the inlet manifolds (where they connect to the head) with some WD40, if they are leaking the WD40 will seal them for a few seconds and the idle will go up.
    if this is the problem you have to unbolt the manifolds from the head and replace the o-rings or seal them with some kind of gasket sealent like threebond.