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RPM drop on ignition check

in General Tech Discussion 6 years ago

  • Re: RPM drop on ignition check

    by » 6 years ago

    Hi Roger. I swapped the plugs top to bottom and the problem stayed on the same ignition. (plugs pretty new, less than forty hours) I might put my new ones in anyway.

    I intend to replace the all the plug leads and get some new caps as well and hopefully that will be the problem. I assume it's relatively straight forward to screw in new leads to the coils, just a bit of work getting access to them.

    And BTW thanks for all the help and advice, it must consume a lot of your time. It's not the easiest at times to find skilled and experienced Rotax technicians down here in New Zealand, the closest ones to me are three hours flying away.

    Peter
      
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  • Re: RPM drop on ignition check

    by » 6 years ago

    Replacing all your parts won’t be cheap. Just ohm out the plug boots. You can test the coils, but I’d be surprised if it was the coil. You caa ohm out the plug wires. Replacing plugs are cheap unless you have the new Rotax ones. Is this one plug black after a 5 min. 4000 rpm run? If all plugs look good or all plugs are firing it won’t be the coil because each coil fires two plugs. My guess would be wire, plug or boot.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: RPM drop on ignition check

    by » 6 years ago

    Hi Roger at 3500RPM + that plug/circuit "comes alive" and performs well with mag drop of only 50RPM or so the plug looks good then after a 4000RPM run. So yes I'm leaning towards a leaky HT lead that performs OK with increased RPM and juice. I had thought I might have an out of tolerance trigger coil but I suppose if the clearance was too great then I'd get two plugs not firing and not just one.

    Can't do any harm anyway to replace the 12yr old HT leads on my engine anyway and I think I've found an equivalent part for the caps. ...Not that I need to but my philosophy over engine maintenance is to focus on how the cost is amortized over the life of the engine.....I've put 500hrs on it and it now has 750hrs total and the only unscheduled maintenance of any substance has been the sprag clutch at about 700hrs.

    Peter
      
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  • Re: RPM drop on ignition check

    by » 6 years ago

    Well new plug leads, checked resistor caps all in spec, new plugs even though I knew they were OK. Zip.

    Checked trigger coil gaps, found A 1/2 was a little over .020. Set it to .014 and engine smoother than ever, RPM drops less than a hundred each side any RPM.

    So the big gap would fire up high but not down low. Very happy, trying to now tell myself it was still worth spending $300 replacing my twelve year old plug leads.. :)

    Peter
    Thank you said by: RotaxOwner Admin
      
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  • Re: RPM drop on ignition check

    by » 6 years ago

    Glad you found your problem. Some times chasing some things down is a challenge. I try not to spend a clients money until all the most common and inexpensive items are diagnosed. About the only thing I'll spend any money on for this is plugs. They're cheap and easy.

    It can certainly be the trigger coil gaps, but most people have to pull the engine to get to the back of it so it is usually best to rule out the most common and easiest to check causes first and then as the last issue pull the engine away from the fire wall and check the coil gaps.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report
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