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Discussion Starter #1
Hi ... and sorry, this question is not about my wonderful Monster but about my old beloved Honda 350 Four -73 ... but maybe the "problem" is more "general" <:O

The thing is that this bike that I've had for some 15 years (and that I have restored to 100% original ... 4 pipes and all)
has started to "missfire" on mid-revs.
Last winter I changed all the bits and pieces in the carbs ... but no change.
The winter before that I overhauled the ignition and changed some wiereing and "connections" for the sparkplugs, and of course I change the plugs every year ... but no change :-(

It spins fine when ideling, and fine above 6000 RPM, but between 3500 and 5500 it's "flat" and clearly not working on all fours all the time.
This problem is also mainly there only AFTER the bike has warmed up (say after riding 15 min)

It's not a BIG problem, the bike is "ridable" and it doesn't stall ... but it's annoying ... so ANY IDEAS ?????
 
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I would check for intake leaks, carb sync, proper function of ignition advancer. Also make sure coils are in good shape!
Good luck.
 

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I would check the ignition. If you have a stock one you might consider swaping to an electronic one. I got a Dyna and coils for my 72 CB 750 and this solved a great deal of problems right away.
 

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Discussion Starter #5
I would check the ignition. If you have a stock one you might consider swaping to an electronic one. I got a Dyna and coils for my 72 CB 750 and this solved a great deal of problems right away.
Sounds good ... only I would like to keep it
as-close-as-possible to the <original> <:-O

But ... where do I find stuff like that "on the net" ?
 
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That is good advice to update the ignition. But if you want to check out your advancer, and I am totally unaware of the particulars of your model, you should see the ignition advance with rpm's with your timing light. If this is a points ignition that does have a mechanical advance, you can just grab and twist the points cam. It should rotate through 20 or 30 degrees and then snap back. If it is stuck or just flops around then you have found a problem. Your light should also pick up a problem if the mark stays still or bounces. It should move steady from the retarded idle position through the advanced position of somewhere maybe 2000-3000 RPM. Again, just general info here, I don't know your machine.
Then to check your coils, remove and check primary and secondary resistance compared to specs you should find in your repair manual. Also with them out, you need to look for leaking or cracks. Also, the resistance changes with heat. Also more voltage is required to fire a plug when combustion pressure is high. When you are accelerating through the midrange rpm's, the pressure is high and a weak coil will cause problems. If you're having problems when light cruising in the midrange, pressure is low and coil might not be problem.
This is just from my personal experience from 30 years of wrenching on various bikes. There are plenty of other things it could be too.
 

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Discussion Starter #9
Thanks for all the advice !!!
Yes I realise you might be "unaware of the particulars of this model" ... but these "general ideas" are very valuable ...
since I'm not at all an <expert> in this field :-(

IF I go for an "electronic ignition" what "potential-problem-parts"
does that bypass ? (the whole ignition advance mechanism ?)

How much "changes" are needed to replace the ignition ?
And are they kinda "general accessories" or are they made for specific bikes and models ?


This is a good point you brought up :
<When you are accelerating through the midrange rpm's, the <pressure is high and a weak coil will cause problems. If you're <having problems when light cruising in the midrange, pressure is <low and coil might not be problem.

The fact is that the problem is <most noticable> when "cruising" at mid-revs ... and at the initial moment of acceleration from there. (after that the acceleration is pretty "smooth")

Does that tell you anything more about the possible cause of this ? (as I said earlier, that made me think it had something to do with the jets ... but that's all replaced ... and no change)
 
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