Yamaha 85AE Problems

I have a Yamaha 85AE 1982 model. It starts up fine and idles perfectly, but on throttel up miss-fires. Seems to be defnit electrical problems as it has a new fuel pump and all 3 carbs have been overhauled also 3 new plugs where fitted. Initial thought was that the CDI unit is faulty but was informed that they are robust and hardly go faulty. Got spark on all three plugs on idle ( even when battery disconnected.) Seem like something is not happy on increased revs. Not sure where to go from here. Does anyone have any sugestions ?

Re: Yamaha 85AE Problems

next step is to beg,buy borrow or steal a DVA meter or a DVM with a DVA adapter and check all 3 primary coil voltages at the problem RPM.

Re: Yamaha 85AE Problems

I'm having a hard time getting hold of a DVA meter. I have a Fluke 123 scopemeter that will show me graphically what the voltage is doing and as a result I would be able to see the peak voltage. Will this do or is there someting that a DVA meter does that I'm not aware of ? What should the coil voltages be ? Also using my multi meter on ohms could I measure coil or stator resistance to pick up any possible problems ? Thanks for the help.

Re: Yamaha 85AE Problems

a graph mey work, never tried it, CDI will sell the adapter for something like 50 dollars.
peak voltage should be in the3-7v range for pulser coil output andlow speed charge coil in the 70 V range at 1500,high speed charge coil,155 above 1500.
you will note the stator charge coil outputs are roughly the CDI(primary ign coil) voltagesw.
all the CDI does is rectify and store the charge coil voltage. it does not amplify.
what your mainly looking for is all voltages remain steady at the engine miss RPM.
all voltages are in a running loaded condition

Re: Yamaha 85AE Problems

Found my fluke 123 scope meter had a peak voltage function on it.. so set it to that and this is what I found :

Two green wires going to the rectifier - 17 Vpk
black/white to pulsar coils - about 7 Vpk but are erratic when throttle up / missfiring.
Red wire from under fly wheel to CDI unit 150 Vpk constant ref earth.
Brown wire from under fly wheel to CDI unit 70 Vpk on idle and dissappears when throttle up ( motor missfires ) ref earth.
Blue wire from under fly wheel to CDI unit also 70 Vpk on idle and also disappears when throttle up (motor missfires) ref earth.

But now motor started doing something else. When it was time to kill the motor it would not shut down. Sounded like it only shut down 1 clynder. Connected clip lead from kill terminal on CDI unit ( white wire ) and shorted to earth. Still did not die. Pulled off plug lead to number 1 and still did not die ! Pulled off number 2 and eventually died.

Re: Yamaha 85AE Problems

double chexk the ground lead to the CDI and the battery ground.
when checking the stator,pulser coils, should be w/r-w/y cyl 1 and w/b-w/g for cyl 2.
low speed charge coil test Br-L(blue) high speed test R-L.