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Discussion Starter · #1 ·
After 6 months rebuilding my CM400T engine finally put it back in and started it up. Started up well and runs good can even ride it up and down my street (dont have full license yet), but wanted to check everything was working so i went over then bike and took 1 spark plug lead off (left side) while running and no change in sound so i put it back on and took the other lead off (right side) and engine died. So in my fairly unexperienced diagnosis that means its firing on 1 cylinder.
So far i have checked:
- Spark plug gap is good
- Has spark
- Carb floats on both sides are filling up nicely
- New air filter

Any suggestions as to why and/or what to check next. Was thinking i may have set the valve tappets wrong so the valves arent being compressed to make combustion???

Thanks,
Matt
 

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Do you have compression spec for the non firing cylinder?
Try spraying starter fluid on that side only and see if it fires.
Best to check the valves are correct first.
 

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Discussion Starter · #3 ·
No compression spec ATM dont have a gauge myself. Ill reset the valves in the morning, also where should i spray the quick starter fluid? Right inside the cylinder thats not firing?
 

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Remove the air boot and spray in there from like a few inches away from the back of the carb. Not too close.
 

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If it's running on both cylinders then ignore that symptom. Both exhaust pipes will be hot if it's running on both. CAUTION: do not touch the pipes
I don't have an answer for why this occurs with this engine but I know it does and it doesn't cause any problems.
 

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Discussion Starter · #6 · (Edited)
juat checked the valves and they are set correctly, and also used the quick start still no change.
LongDistanceRider: both exhaust pipes get hot, but the cylinder that isnt firing (left) doesnt get nearly as hot as the one that is (right). Is it possible that both cylinders are firing even though when i take the lead off the right plug the bike dies, but if i take it off the left plug nothing happens?

Sorry if this is a lot of questions, just frustating for me that only 1 cylinder seems to be working yet it runs pretty smoothly (need to adjust idle still though), i will post a vid of it running in a few once the head cover is back on.

Thanks again,
Matt

Video file to large to post :(
 

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Take a look at the left spark plug, is it wet or dry?
 

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Both pipes should be the same temp or close. Colder temps indicate not firing or running richer than the other. Since you have idle and can ride it I'd guess it's rich.
I'd check the sync on the carbs and adjust as needed. Then adjust the mixtures.
 

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Discussion Starter · #9 ·
Left spark plug is wet and the right is dry.
guess next step is to get my hands on a vacuum gauge and find out if that the problem then sync the carbs. if not then take out the carbs and re clean them.

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Put in a new spark plug first.
 
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