Spark loss port cylinders 200sws

I have a 1990's sws 200. Started running rough. I found all
The port cylinders cold when I checked. All the stbd cylinders
Appear to be firing. Did compression, all are 120 psi or within 5 lbs
I am thinking major electrical part failure. Before I look
For mobile yamaha mechanic, is there any simple thing I
Can do to narrow down the cause ?

Thanks, Steve
( sent over from classic mako forums)

[Aleutianwest]

Check for dirty grounds off the CDI on that side of motor and check trigger connector see if corroded

Grounds

I will definitely go thru all wires again.

So far I have only checked the 2 plugs
That reside under the plastic box
At the back of the block. The connections
There are flawless.

I did find one tan wire ( of 2) that had a
Worn thru insulation, I need to see if that
Wire is rotted inside.

One other clue here is that I found out
By toying with the wires and tapping
The box at the rear of the block, that I
Can get the stbd side to go dead, and then
Return as well.

This tells me I really need to go over
Every wire before taking her in to a mechanic.

Any other advice, especially from someone
Who had one side lose spark will be greatly
Appreciated.

found problem....

Im an idiot.... I assumed since it appeared that half the engine was dead that it was a spark issue. I dont have advanced spark test gear so I called in a local mobile mech. He tested spark and compression, all was great there he said. (MY BAD for not checking for spark at each cylinder for sure.)

He said the issue is FUEL, most of the cyls were not firing due to Gummed up carbs. He's recommending to rebuild /clean all carbs as well as the fuel pumps. Cost: 2 days $650.00

I have done plenty of carbs in the past and its a messy job...I decided to let him do it.

About the FUEL:

I initially thought that the carbs being so bad was strange since I use the boat often and always use startron to help with the 10% ethanol gas we have here.

But I trust this Guy so I thought about fuel for a second.

Then I did remember that after 12 good clean months of running every week or so, I found a bunch of gunk in the filters last time I used the boat...both the Standard water sep. that I have near the tanks under the C /console, and in the Racor near the engine had strange looking dark crap. I poured our the racor and saw what looked like brown smoky colored sludgie liquid below the mormal looking fuel at the top of the coffee can. It wasnt dirt...it looked like a heavier , smoky, more orange gasoline..

I cleaned these filters out and assumed all was fine....But that was a month ago and I had not used the boat since so I never discovered that this mess probably got into the lines/pumps/carbs.

What bothers me is I really suspect ETHANOL after talking to the mechanic.
HE recommends using NON ethanol gas, if I can find it.... However, I just filled up on 87 octane from the gas station....

ANybody have this problem?

Now Im worried about it happening again...I definitely cannot peel off almost $700.00 each time this happens !