I've recently acquired an MC21 that for the past few years sat in the weather without much of its fairing. most of the electrics did not work and to date I have repaired the lot apart from the uppermost plug has no spark.
I have tested the pulse generators and even swapped them around and both will work on the front (lower) plug but not the upper one. I've also swapped coils and plugs (new) to no avail.
I have checked all the wiring and connectors through to the computer and from the computer through to the coils etc, and I have continuity and there is no voltage drop between the connections.
Someone has suggested I can grind lobes off the flywheel and that will solve the problem but I have doubts it would work, anyway, I can't see bodgying a perfectly good flywheel makes any sense.

I've noticed the lower pulse gen/flywheel lobe clearance is .010" and the upper (non firing) one is .025". I would dearly like to determine if this is the correct specs and if both pulse gens are in fact identical or if the upper one has a longer pole- mine hasn't, it's identical to the lower one.

I haven't tried to start the bike as yet so really I have no idea if the upper pot will fire up once the front one fires. It might be like some of the Mitsubishi Lancers that need the first pot to fire for the computer to energise, but I'm grasping at straws!

I am a retired motor mechanic with extensive experience in late model Mitsubishi vehicles and specialised in electrical problems but this one has me scratching my head. I don't know whether to buy another computer or to just fire the bike up to see what happens.

Any advice greatly appreciated.

Can't see how griding lobes off the flywheel will help, that's not how Honda intended for it to be!

Sounds like you may have a half fried PGM (the computer). Have you removed the top of it to check for any burned out bits of the potting compound?

thanks for your reply. I agree with the lobe grinding thing, makes no sense, besides, if one lobe is all that's required to ignite both plugs then why isn't it doing so now?

I haven't looked into the PGM as yet but that was my next move. I can have it tested in the city, $100 just to hook it up without any repairs if needed so I'll check it out myself first, the smell test is usually a good indication once the lid is off.

I'll let you know the outcome.

99.9% when the PGM fails there is no spark at all even if the problem is solely on one side on the ignition.
Your issue should be in other part of the electrics.
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2Tracelab wrote:99.9% when the PGM fails there is no spark at all even if the problem is solely on one side on the ignition.
Your issue should be in other part of the electrics.

I must fall into the .1% then,as I've had this happen,(no spark on one pot)and replacing the PGM cured the issue!

I decided to test for spark at night in the dark just to be sure and have spark at both plugs but it appears weak. Spark is a nice white colour at least.

The front plug, the lower one, seems to have regular spark on crank but the upper one is intermittent but at least it's there and gives me hope. I'll re-check all connections including the earth points.

Can anyone please tell me if the two pulse generators are identical and if the air gap on the uppermost one is supposed to be .025" whereas the lower one is .010" It would be nice to be able to either chase up another set or finally be able to delete this area as a problem.

Is the front plug No. 1?

Gap should be the same on both lobes.

No1. is the LH cylinder.
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2t-racelab.com

toneless wrote:Gap should be the same on both lobes.

No1. is the LH cylinder.

Thanks for your reply and apologies for not responding sooner, I do appreciate your input. I've removed the gens (again) and checked all measurements and they are identical apart from a lug on the body of the lower (rh) one. I was hoping the suspect one was broken off but it doesn't appear damaged at all, and as both units magnet projections are the same I'm very confused.
I've now set the bike up to run and will test voltage readings from the gens to the pgm and from the pgm to the coils & plugs. I'm hoping the problem will appear and be apparent.

I will advise and thanks again.