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Author Topic: Tech Question - what would cause a plug to not fire at higher RPM's?  (Read 6488 times)

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Offline madmtnmotors

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Re: Tech Question - what would cause a plug to not fire at higher RPM's?
« Reply #25 on: October 20, 2016, 08:50:18 AM »
Quote from: Geeto67 on October 20, 2016, 08:31:27 AM
So I swapped out the plug, and the high rpm no fire went away. So I guess it was just a defective plug.

I figured out the running rich problem, the carbs on the bike are 657B units running 120 main jets. The original carbs on the bike (which were unusable) are 064As running 105 jets and by the way apparently the slow jets, the emulsion tubes, the needles, the jets, and the settings are all different for these two different carbs. I found another set of 064A carbs in my stash and am going to rebuild those.

Glad you got it sorted. 120 main is definitely quite large for a near stock setup.
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Offline Geeto67

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Re: Tech Question - what would cause a plug to not fire at higher RPM's?
« Reply #26 on: October 20, 2016, 11:12:41 AM »
Quote from: madmtnmotors on October 20, 2016, 08:50:18 AM
Quote from: Geeto67 on October 20, 2016, 08:31:27 AM
So I swapped out the plug, and the high rpm no fire went away. So I guess it was just a defective plug.

I figured out the running rich problem, the carbs on the bike are 657B units running 120 main jets. The original carbs on the bike (which were unusable) are 064As running 105 jets and by the way apparently the slow jets, the emulsion tubes, the needles, the jets, and the settings are all different for these two different carbs. I found another set of 064A carbs in my stash and am going to rebuild those.

Glad you got it sorted. 120 main is definitely quite large for a near stock setup.

And yet, stock for some models of cb750 carbs. Strange.
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