[JuicyJerry]

Bike isn't running. Turns well and fuel is making its way to the carburetor.
I suspect the spark plugs are the issue, failing to ignite the fuel/air combination.
The plugs look good visually. When I test them they give a fat spark but only once when I begin the electric start. After that it cranks but no spark.

Is that normal? Shouldn't it spark every crank of the engine?
If it was the electric start, wouldn't I be able to ignore it and start it with the kickstarter?

thanks

Can post pics of anything if needed

 

[Bill H]

The CB 400 A motor is a 360 degree motor. also known as a wasted spark motor. Both pistons rotate together and both plugs fire at the same time. If number one fires on the compression stroke number two will fire on an open exhaust valve. Thus the wasted spark name. You should get a spark at both plugs every other revolution . The motor runs from the CDI and you dont need a battery to get spark at the plug so it should start with the kick start. Power comes from the stator ,to the CDI, to the coils thru the leads to plug cap to the plug. Easy stuff first. switch on, kill switch in run position. I suggest you go to an auto parts store and pick up a spark tester. About $15.00 bucks. If the tester shows spark look for the problem at the wires ,caps, or plugs. If no spark then you will need an OHM meter and a full service manual. Use the tests in the manual to check the coils and stator, you cant test the CDI. If coils and stator test good its probably the CDI.

Bill H

 

[drydreamer]

The red neon plug caps that flash when HT passes thru them are a really usefull bit of kit.

A digital multi meter is also a good bit of kit, ohms, DC and AC volts etc..

Ignition related wires from the stator will produce AC volts when engine is cranked, rising with revs...

Your problems sounds like a bit like a failing cdi, but check all ign related ohms and AC volts first along with connections...

HT leads are not removable, any wobble of the HT leads in coil towers ?

Sometimes the handlebar kill switch can " leak" electrically...


Disconnect the black/white cdi kill wire and try again, earth that wire to kill ignition.

 

[Bill H]

Red neon plug caps are great for a single operation I like the spark tester because you can use it on any motor that has a spark plug. Install in between the plug cap and the plug. After the test remove it and put it in your tool kit ready for your next test.

Bill H

 

[Jack03]

I have just replaced the ignition coil on my cm400. I had my coil fail and it sounds very similar. I used a simple voltage tester to see if I was getting a spark.

 

[JuicyJerry]

Thank you all for the responses!
I am blown away by the knowledge and willingness to share said knowledge on this forum.
I am doing a large move but will update you all on the situation when I have time. Mid july sometime probably