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Thread: 4151 Loses Spark Energy at High RPM

  1. #1
    mikejr Guest

    Default 4151 Loses Spark Energy at High RPM

    I have 2 identical Jr Dragsters with 4151's. One runs fine; the other drops out during the run (for 2-3 seconds at a time), at ~7500 RPM. Have switched the 4151's, pickups and coils (8232) between the two cars - does not help. The problem car still drops out, so the ignition hardware seems OK. Switched entire fuel systems (pump, carb & lines) - does not help either; the problem car does not get down the track. Battery voltage is logged, and never drops below 14V.

    The car starts and idles normally.

    The two cars are jetted identically (alcohol). If I drastically lean the mixture on the problem car, it does get down the track, but is too lean to leave the starting line consistently. It seems that there is not enough spark energy to fire under load, when there is more fuel

    There is no visible difference between the 4151 LED responses or the spark (looking at a grounded plug while 'firing' the pickup. Could this be a problem with the flywheel magnet strength or ???

  2. #2

    Default 4151

    Hello,
    There could possibly be an issue with the polarity of the magnet in the "problem" car's flywheel. The South side must face towards the pickup, this might be something to check for if you haven't already. Have you load tested the battery? Although you have 14 volts there may not be enough amps to run the ignition at higher RPM's. The only other thing I can think of is to check your ground connections as ground issues can cause this as well. Let me know how it goes. Thanks, Bret- MSD Powersports Tech

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