Yamaha 90 no fire on cylinder 1

[brodmann]

My son has a 2004 Yamaha 90 TLRB. Cranks and runs great until you try to get to WOT. Bogs down and falls on its face. Idles great. After doing a little checking we're finding no fire on cylinder #1. Swapped coils around and still just #1 not firing. It's getting gas to plugs, but no spark. Compression is 118 to 120 (don's remember exactly which cylinder had what, but 2 were 118 and another was 120. I've messed with a lot of motors over the years, but the last ignition problem I had with one required changing the points, so I'm not real familiar with the newer models when it comes to ignition issues.
I appreciate any ideas you guys might have.

 

[99yam40]

I believe that motor has pulser coils that feed the CDI to tell #1 & #3 when to fire those cylinders.
need to test those inputs to the CDI

 

[brodmann]

Sorry, you're over my head. How would I do that?
Also, my son wonders if it might somehow be in limp mode. It accelerates fine up to 2300 RPM's. Always starts to studder beyond that point. If he gives it full throttle it will accelerate past that, but immediately stumbles and returns to 2300 RPM's. No lights or alarms though.

 

[99yam40]

make sure all alarms and gauges work as they should to make sure .
But nothing that I know of will just kill #1 cylinder spark except the CDI not getting the signal to fire it .
could be a bad wire/connection, bad pulser coil maybe.
are you positive #1 has no spark at any time?
do a search for CDI electronics troubleshooting, or get a service manual for that motor

 

[boscoe99]

Test equipment and test procedures are needed. Firstly to verify that the number one spark plug is not firing at any time. Presumption being that this has already been done.

But then I am not understanding how the motor is running great below WOT RPM if the number one plug is not firing. With one of only three cylinders not firing, seems to me it would not be running well. Perhaps even at idle RPM.

The system is then tested to determine why no ignition from the number one spark plug. Could be any one (or more) of several components. Or a wiring issue.