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  1. #1
    masta2000's Avatar
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    problem getting max rpm with rr ecu

    the rotax racing ecu i have has the information bellow:
    name : racing only
    dataset: #h3j66r3a
    project: 1503 scic
    date: 26.02.2006
    remark: MY 2005

    i'm using it on my 2004 rxp. i had it dialed in at 8500rpm and everything was running great. one day i check the slack on my camchain and found a bit of slack so i loosened the gear and it backed up slightly and i tightened everything. now the 1503 lines line up perfectly with the head and there is no slack. at the same time i reset my TPS by putting stock ecu back in and resetting and then putting the rr ecu back in. upon taking it out i couldn't get over 8240 rpm, for no apparent reason. no boost leaks and charger is at 14NM. then i realized i hadn't taken off the piggyback harness for the knock sensor; took it off and lost another 400rpm, was only going 7800. i tested the machine on the hose and i could only get 8400 without the piggyback and with it back on i could get 8600rpm. now assuming that it ran perfectly before i did all this, can anybody pinpoint the problem here?


  2. #2
    masta2000's Avatar
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  3. #3
    Vern's Avatar
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    It sounds like you might have changed cam timing ... thing is, I am not sure I understand what you did ... there is no way to change slack in the cam chain. Once you hang the chain and cam gear and tighten the bolts, the tension in the cam chain is maintained by the camchain tensioner in the block ... and that is non-adjustable too.

    So I guess I was not sure what you did and why ... loosening the cam bolts will allow the cam timing to change if there happens to be more tension on one side of the chain than the other, which would be very normal actually. Maybe I misunderstood something, but it sounds like all you accomplished by loosening the cam bolts was to allow cam timing to slip/change ... so if I did follow this correctly, you need to loosen the cam bolts and get cam timing back to where it was before.

  4. #4
    masta2000's Avatar
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    thanks for the reply, i had tightened the bolts a bit by mistake when installing the gear, so the gear was leaning a bit to the left, making it slightly advanced, but leaving the left side of the chain slack a bit. so when i loosened the bolt, the tensioner pulled it tight and brought the gear flat with the head, and at the same time retarding the timing. i am just not sure if this is the problem because the gear can not go on in any other way and i am perfectly TDC.

  5. #5
    Vern's Avatar
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    OK, got it. So it was running 8500, and then you pulled the valve cover and checked cam timing and loosened the bolts? I guess I am still not clear of why the cover was off and what was being done? Did you pull the head or cam and remove the cam gear? I am not sure if you might be a tooth off (not unless you took the gear off) or just changed cam timing by where the bolts now sit in the cam gear slots ...

    How does it run elsewhere? Idle smooth, low rpms smooth? Did you check/know compression before and compare to compression now?

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