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Discussion Starter #1 (Edited)
I'm having troubles diagnosing the poor idling/knocking on one of my two CM400A's.

I drove this in high school and it hadn't run in years until I got it running 3 years ago, that's when it started doing it. I only got to drive it 10 minutes and the stator went. After spending days chasing a no spark issue, I recently found another bike to diagnose with.
If something's causing it to destroy stators, I want to find it before I find myself hunting for another hard to find stator.

Also did;

  • New Battery.
  • New carb kits.
  • New spark plugs.
  • New spark plug wire boots.
  • Fresh non-oxy fuel.
  • Checked the valves and they are at .003 and .005
  • Tightened the timing chain.

If you have a some time, please listen to it run and tell me what you think. It idles fine and slowly goes into a poor idles condition then knocks like it's in the head and then idles fine again. It's almost like a correction.

Long Knocking Video:
https://youtu.be/uXkqotcmVfg
At :40 – Just about knocked, expected it to knock.
Knocking:
1:12
2:44
3:37
3:54
3:59
4:05
6:31
6:51

Messing with wire, idle speed up at 5:11 and 5:24. Haven’t determined if this is related.

Short Knocking Video:
https://youtu.be/CVxkZf3lJR8
Knock :32
Revving

You’ll notice that revving off of idle shows kind of partial knocking or initial knock, but not a full knock.

Any advice would be helpful.

Thanks
 

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Correct valve adjustment is .004" intake and .006" exhaust dead cold.
I'm horrible with noises but what you're describing sounds like the balancers knocking. They have rubber dampeners in them to cushion the halves from banging, when those go bad they disintegrate leaving little bits of hardened rubber in the crankcase. I would suggest adjusting the balancer chain and see if that has a effect. Someone should be along that can hear and may have a better idea of the noise.
 

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I don't hear anything to worry about. As Jim suggested, adjust the valves (cold engine). Then balancer chain. Then start it up and adjust the cam chain. I believe you will hear a different engine.
 

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Sounds to me like a misfire also. Possibly a plug shorting to ground or possibly a brief interruption in flow through one of the idle circuits.

Definitely not something I'd get wrapped around the axle about, turn your attention to making sure your butt fits the seat.
 

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Discussion Starter #6
Balancer Chain Noise

I adjusted the balancer chain. It was WAY lose. I had to move the adjuster plate 2 splines, but the punch mark is still well within spec.
It idles quieter, has a little whine, but as soon as I speed it up, it now sounds like the chain is rubbing or dragging across something inside. I had to set it by hand as the tensioner spring wasn't strong enough after the spline change to make any adjustment on it's own. Listen to it again, did I get it too tight?

https://youtu.be/feD0VzIAOKc

Also, I found the knock, it's coughing back through the carbs. (don't know why yet)

Thanks for the help everybody!
 

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Seems to be running quite well considering the loose hose clamp.

I didn't hear anything alarming.
 

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Discussion Starter #8
Seems to be running quite well considering the loose hose clamp.

I didn't hear anything alarming.
The carbs are in there lose, running the throttle lever with the screwdriver.....

There is clearly a rattle now that was not there before, it sounds to me the chain dragging across something. Just don't know why it does it when I rev it up.
 

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Loose carbs = vacuum leak = intake backfire. Get the carbs secured and that should clear up the problem unless the insulators are bad.
 

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Discussion Starter #10
Loose carbs = vacuum leak = intake backfire. Get the carbs secured and that should clear up the problem unless the insulators are bad.
I was going to say it didn't make any difference if they were tight or not, it still does it just the same and that at this point I was only interested in the chain noise, but after reading to the end, you got my attention with the comment about the boots. If they are leaking, and it could easily be the case, it's been my original problem all along.
Thanks.
 

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Discussion Starter #11
Laid the bike over and loosened the chain by turning the slotted bracket from the end back to the center, all runs good now. Must have been just a tad too tight.
Still trying to figure out the backfire at low idle. Even just a little choke and it doesn't do it. Seems a little lean?
Throttle is responsive and smooth off idle and at any point.
 

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Sounds like you're on the right path, carb popping/backfire is a lean condition in most cases and definitely in yours since adding choke cures it. If the insulators are hard enough that you can't leave a thumbnail dent in them they need replacement.
DSS has the early version in stock David Silver Spares USA - 16211-414-010
 
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