1984 90hp yamaha only running on 2 cylinders

[seahawk108]

my 1985 90 yamaha when cold runs fine when it warms up only fires on 2 top cylinders. she wants to fire occasionally on the bottom cylinder, i have swapped coils with #2 cylinder with no change in the third, #2 still fires fine #3 still not firing properly. took carb cleaner and sprayed in one cylinder at a time choked down when sprayed into #1 & #2 made no difference when sprayed into #3. anyone have any answers please help. thanks seahawk108

 

[rodbolt]

Re: 1984 90hp yamaha only running on 2 cylinders

check the CDI output on #3, will take a DVA meter, also check the pulser coils and high speed charge coil output, if all tests pass but the CDI output you may have a bad one,
that system uses a pulser coil on 2 and 1 but 3 is "synthesised" by the CDI.

 

[seahawk108]

Re: 1984 90hp yamaha only running on 2 cylinders

what do you mean by dva meter or did you dca (dc ampmeter) thanks seahaw108

 

[rodbolt]

Re: 1984 90hp yamaha only running on 2 cylinders

most digital meters are averaging meters with a built in display delay, peak reading meters have the movement set up to show voltage peaks, thats why most Digital meters need a DVA adapter to display peak voltage.Digital Voltmeter Adapter.
peak reading meters are allmost always analog, I used some specialty stuff in the USN but its rather costly for a shop thats not paid for with taxpayer dollars

 

[seahawk108]

Re: 1984 90hp yamaha only running on 2 cylinders

robolt i have a dva adapter coming for my multimeter. where can i find instructions on how to check the cdi and pulser coil and what the readings should be. thanks seahawk108

 

[rodbolt]

Re: 1984 90hp yamaha only running on 2 cylinders

tune up spec guide has it, stator output low speed, Br+ lead,Blue negative lead, 85V cranking loaded and 75V at 1500 RPM loaded, high speed, +lead on the red, negative lead on the blue. 45v loaded cranking and 155v at 1500.
puler coilw/r+ lead-w/y and w/b(+)-w/r 2.5V loaded cranking and 7 v at 1500.