[just2wheels]

Hey all,
I recently bought a 1979 cm400a that I thought just needed a carb job. I have now rebuilt the carbs and it runs fine until I put it in gear, it then stalls out if I stay at a stand still. If I immediately give it throttle it will stay moving until I try to stop and it will just die. Any help would be appreciated.

 

[Bill H]

Your bike has an idle stabilizing circuit. Timing is 7,5 degrees at idle in neutral at about 1250 rpm. When put in gear the change switch sends a signal to the cdi and raises the timing to 15 degrees and the idle to about 2200 to compensate for the load from the torque converter. You might try putting the bike on the stand and see if the timing changes when shifted in gear. Do you have a FSM? timing mark"FN" 7.5 degrees in neutral . "F" mark 15 degrees in gear. At idle. This from my CB 400 a manual but should be the same.

Bill

 

[just2wheels]

Thanks Bill, I'll go try that today if I can find the time. Where is the switch located?

 

[Bill H]

The change switch is on top of the upper case under the right carb. The change switch rely is under the left side cover. If the starter motor turns over in neutral and your 1st and 2nd lights come on when you put in gear its probably not the change switch. The rely sends a signal to the CDI when you put the bike in gear. to raise the timing. this is done in the CDI .Put the bike up on the center stand and start it up. you will need a pulse tack to check the rpm since you dont have a tack. try to do it by ear if no pulse tack. if it runs ok in neutral put in first gear and see if it will run on the stand with the rear tire off the ground. You will be able to tell if the timing changes when you put it in gear as you can hear it. It may be as simple as raising the idle speed. Let us know what happens when you put it in gear.

Bill

 

[just2wheels]

So while trying to check timing. I found some interesting things. 1st-the idle will not stay consistent. 2nd-the rotor does not have an "FN" mark. 3rd-it does not seem to change RPM (any more than usual) when I put it in gear. The rotor looks pretty new...is it possible that it was replaced with one meant for a non-hondamatic and that is the problem? I also saw on a quick search that the "a" models used nippon-denso systems and the non-"a" models used a hitachi system. Is this true? My CDI is nippon-denso but the rotor is hitachi.

 

[longdistancerider]

The manual rotor has a T, F and 2 lines in it like this one