QuestionQUESTION: I have a cm400t it starts and idals bt only fires on the left hand side. when i rev it the right hand side hits sum but it just goes in and out. i pulled the plugs and the right side has weak spark, i have new plugs wires and ignition coil my carbs are rebuilt and tuned so im left to think my cdi box is bad but there is no test 4 this model i have the book 4 it. i didnt want to buy a cdi until i asked a professional if this could realy be the problem. any knolege would be a great help. thank you
ANSWER: Charles, I can offer what I have read on another website about troubleshooting the 400-450T ignitions.
Honda CB400T ignition test information: from the cdimagician on Ebay
The measurement of the Yellow and Green wire coming from the coil may not have a reading.
The coil primary winding may have opened up. This is an infinite resistance, meaning a bad ignition coil.
The measurement of the Pink and Green wires going to the stator may not have a reading.
The coil in the stator may also open up. Resistance of the wires could be less than 135 ohms. The coil could have shorted windings. Not enough energy will be developed in the stator coil for the ignition.
The measurement of the resistance of the White and Blue wires may not have a reading. This coil on the stator may open up. Resistance of the wires could be less than 85 Ohms. Shorted windings in the stator coil will keep it from developing enough energy for the ignition.
The measurement of the resistance of the Brown and Light Blue wires may not have a reading.
The coil on the stator may open up. Resistance of the wires could be less than 207 Ohms.
The black wire with the white stripe goes to the kill switch and key on the handle bar…...
If the kill switch is on or the ignition switch is Off the black/white wire will be connected to the frame of the motorcycle.
0.0 Ohms resistance to the frame.
The motorcycle will not start up, ….or will shut down.
If the kill switch is off and the ignition is on there will be no connection to the frame.
The black/white wire resistance to the frame will be infinite or no reading on the meter.
With no connection to the frame, the bike will start up,…. or will be running
Pulse generator test 50-170 ohms Blue/yellow to Green wires
Alternator charging coil measure between all three yellow wires .6 to 1.1 ohms between leads
Ignition coil primary windings .1 to .3 ohms Rebel 450 .55 to .65 ohms all others.
Ignition coil secondary windings 7,200 to 8,800 ohms Rebel 450, 7,400 to 11,100 ohms all others
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Did you check the resistance values of the spark plug caps? It isn't clear to me if you used the old ones on the new coil or not.
The coil is double-ended, so fires both plugs each revolution. To have a "weak spark" on one side, indicates a bad spark plug cap. The CDI box doesn't control each cylinder, only when to trigger the coil, which fires both plugs at once. Both spark plugs must be grounded to check spark. One side has a reversed polarity when the coil fires, so you may not see the spark as clearly on one plug.
If the bike isn't running on one side, then the problem is more likely low compression (tight or leaking valves?) or the carburetor isn't fueling that side properly. The other issue with these carbs is the air-cut valves. If the diaphragms fail, you get an air leak at idle, which leans out the mixture beyond specs.
Bill Silver
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QUESTION: I havnt had time to work on this bike or run the test yet but to answer your ? i used new sp wires and caps and got new plugs. i switched sides with the plugs and same problem. i also swiched sides with the plug leads and had the same problem. my carbs are freshly rebuilt with new diaframs so i didnt suspect bt mabe they arnt working properly so il doube check that also. i did suspect compresion bt the test showed good compression and 5 psi higher on the side not firing. your answer was very helpful because i couldnt find the test specs but if you have any more advise or knowlege as to the problem i am haveing going by this email it would also be of great help in narrowing down my problem when i next get to work on it. thanks a great deal for all the profesional help so far, i know nothing about this bike but i am learning everyhting i can as i go.
AnswerCharles, with the problem remaining on the right side, after all the switching of electrical components, then the probable cause lies with the fuel or compression.
Make sure the valves are adjusted to specs first. When valves are too tight they can remain slightly open under operating conditions, as the stems grow somewhat in length.
It seems like that the right side carb is either lean due to fuel flow restrictions, low float level, blocked idle jet or air leak at the intake manifold.
Run it a little and then pull the spark plugs to see what they look like. Check for excess fuel or oil, or if very dry, perhaps lack of fuel or an air leak. The intake manifolds become very brittle and can crack down where the carb stub mates with recess in the manifold.
It may be that you are not seeing the spark well on the right side, due to the reversed polarity on one plug. Spark actually jumps from ground to the center electrode on one side, while the opposite side jumps normally from center electrode to ground. Put a very thin piece of paper in between the gap and see what side the spark comes from, sometime. Always have both plugs grounded when checking for spark. That is the only way they can complete the circuit. Having one plug ungrounded can cause a voltage buildup in the coil that can short it out internally.
I don't think this is an electrical problem.
Bill Silver
