SOHC.co.uk Forums > CB750

Acceleration Misfire

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Skoti:
Carb slide needles in the wrong position?
Set too low and giving too a weak mixture.

Johnny4428:
Advance mech running freely?

McCabe-Thiele (Ted):
I always think poor cold starting indicates a lack of fuel so running a tad on the  lean side. Other reason might be the ignition is a tad retarded.
If your E- ignition has separate adjustments for 1/4 & 2/3 might be worth checking the timing on both, as is the advancer unit if you are using the original mechanical unit.

Saesneg Shaun:
Thanks all, i'll try turning the screws in to richten it up a bit. I was told too lean and the revs hang when I blip the throttle and too rich revs will bog down then recover. I'm running the stock airbox & filter and the advance mech is replaced with the boyer kit.

K2-K6:

--- Quote from: McCabe-Thiele (Ted) on September 05, 2024, 09:38:00 AM ---I always think poor cold starting indicates a lack of fuel so running a tad on the  lean side. Other reason might be the ignition is a tad retarded.
If your E- ignition has separate adjustments for 1/4 & 2/3 might be worth checking the timing on both, as is the advancer unit if you are using the original mechanical unit.

--- End quote ---

Boyer system has no adjustment between the two sets to be moved. Effectively, the backplate is set up geometrically in manufacture to fix them at exactly 180 degree apart, no seperate spacing needed to cause problems.

In addition, they fire all four plugs at every event of timing ..... at every 180 degree increment that passes the trigger point.

Also, there's no "advance" as such. They set the trigger point at maximum timing point (hence installation notes to check it above specific rpm) then they delay the timing point in software based on engine rpm to give a retarded effect for low crank speed, this detected from pulse count register as you crank it. 

Also facilitates "multi spark" at low rpm firing to try and mitigate plug fouling etc and provide more effective cold start.

Its a pretty comprehensive system solution to replace points with.

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