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Discussion Starter · #1 ·
A few weeks back I was having trouble with getting a spark on only one cylinder and soaking the other one wet with gas. I did the multimeter tests that I found on YouTube for checking the coil and decided to replace it. I also removed the regulator to replace it, but installed the old one back when I wanted to test the new coil. I wanted to make one change at a time to make it easier to isolate the issue.

Here I am with a new coil and the old regulator/rectifier and I can crank and crank with no start or spark. Immediately prior to this it was running nicely, first on one cylinder, but once fresh (and dry) plugs were installed, on both cylinders.

I am going to recheck the valve adjustment to see why only one plug gets wet when cranking, but where is the best place to start chasing a missing spark? Could it be an issue that the new regulator might cure?

I did find this:
https://www.hondatwins.net/forums/6...400-450-cb450sc-manual-trans-1978-1986-a.html

Would the info be the same for a CM200?

Thank you sincerely and hugely,
Justin
 

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The CM200 has a 360° crankshaft, so you should also have only one ignition coil (dual tower).

If the problem is that you're not getting a spark on one side, then the only possible cause is one of the following:
*Bad ignition coil
*Bad spark plug wire or plug cap on the affected side
*Base spark plug on the affected side

It's usually a safe assumption (not always, but usually) that the coil is good if you've replaced it, so we'll set that aside for now. The plug wires are also part of the ignition coil, so we'll assume that's good as well. Replace the plug caps and spark plugs for peace of mind. I don't normally advocate "shot gunning" parts at a problem, but in this case the parts are cheap and if you don't know how old they are you might as well take care of it.

OK... now to the other possibilities.

Besides a spark at the correct time, your engine also needs compression and the correct air/fuel ratio.

Compression is a lot easier to check than AF ratios, so get that out of the way. Good compression on a cold motor should be at least 110 PSI. In good condition, it's not uncommon to see 150 PSI. Cylinder pressures should also be within about 5% of one another.

After compression tests, the only other possibility is the carbs. If the plugs are wet and the cylinder still isn't firing then you have an air issue. If the plugs are dry then you have a fuel issue. Air issues are usually cause by incorrect carb sync where fueling issues are plugged jets. Starting fluid can also help identify fueling and air issues because ether is a lot less sensitive to ratios and compression than gasoline.
 

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You have a points type ignition system so that link you posted doesn't apply.
Compression on this engine new was @170 PSI on a hot engine.
If you're using something other than the NGK sparkplugs switch back to them, C7HS.
 

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I'm going to go with compression in that cylinder......
Points ignition fires BOTH plugs simultaneously, and both plug wires must have an active ground path (usually through the plugs) for either side to fire....
If one side is timed accurately enough for the engine to run, both sides are.....
Both cylinders share a common/single carb......
 

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Discussion Starter · #5 ·
Thank you all. I printed this out and will start attacking this over the weekend. Plugs are new, compression WAS good when I checked it a few months back, I drive old cars so starting fluid is an old friend that hasn't helped here. Fingers are crossed for good results.
Justin
 
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