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Old 07-08-2020, 06:09 AM   #4
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Join Date: Jun 2011
Location: Northern Indiana
Posts: 2,328
Default Re: Hei conversion on a Yamaha J38 G2(?)

Originally Posted by cgtech View Post
I see this one hasn't been touched. I'll answer. Yes, it probably can. (I wouldnt, so dont ask me how). But, heres why it shouldn't be done. The stock ignitor modifies ignition timing based on rpm, less timing at low rpm for easy starting, .more timing later for more power & better power/economy at higher rpms.
A HEI can probably be made to trigger the coil, but it cant do anything to advance the timing as rpms increase, so the base timing that would allow easy starting would be the timing used across the entire rpm range. That's not good. The "lazy" timing that allows easy starting is far from good for the rest of the rpm range of the engine. Also, the crank trigger at the flywheel is not adjustable to "pick a better spot" either. (That task of "pick better timing" was handled by the original yamaha ignitor based on rpm). Can it be done, probably, should it be done, probably not.
I have come across a couple earlier Yamahas that people had already done the HEI conversion - and hated it. From what I've seen the OE ignitors retard the timing for start up and low RPM running, then allow the timing to advance (to about 30 BTC) at speed, not the other way around. The placement of the pickup puts the natural base timing at 30 degrees and the HEI coil can't modify it. They run OK once started but buck hard, try to run backwards, take many attempts to get started.
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