'03 90hp outboard surging issue

[99yam40]

the 93 90 uses 1 two wire pulser,wire colors w/r-w/b, to fire 1&3,cyl two is sparked by the CDI based on CPS inputs.
84-91 uses two pulser coils and #3 is made up by the CDI and CPS.

Thanks Rodbolt, for the difference in info for the different year 90 motors.
I was way off in my thinking

But how does the 90 limit/reduce RPMs during alarm situation like overheat?

Retard timing or miss fire multiple or maybe all cylinders randomly?

[rodbolt17]

according to the training manuals, which BTW are absolutely unessary, it mis fires.
that's why its so violent.
a simple retard would simply make it run sluggish.
but that is a very hard concept to grasp as most back yadigans aint gotta clue of why you have to time ign to piston travel.

[SeaDawg3]

yup, most NC podunk back yarders. bailing wire n duct tape. J/K

[throrope]

I suggest an organized approach.

I lost a cylinder, cleaned the carbs, got it back for twenty minutes and then thinking ignition schlepped the rig to the boat yard for an expensive carb rebuild. A fouled fuel system was the culprit. I could play with it all season and with every run I'd plug the carbs.

To enable the shop to stand behind their work, I replaced everything upstream of the quick connect. I now empty the boat of all gas and air dry the tanks upside down between trips and haven't had issue since.

Recently a buddy elsewhere posted a failure on two year old fuel line he once touted as the end all. Seems our lovely ethanol had the last say. I pulled the same two year old hose from my boat, stepped up to the next quality for the first and last three feet and ran 3/8" soft annealed copper with flare fittings in the middle. Now I can swap out those six feet every year in 15 minutes for 15 bucks.

These outboards are relics of the gas or spark age and '03 is not old. Since you can fire it up, I suggest you restart the process on the less expensive gas side. I suggest throwing out all the cheap stuff upstream of the connection on the motor. Then test and clean everything sequentially from there to the block. Along the way insure every step in the fuel path doesn't fall victim to an unresolved upstream issue.

Come to think of it, I recall a diaphragm on the electrothermal valve that serves as "choke" on our 90 hp. Seems plausible a failure there could cause grief after heating up.

Hope this helps, good luck and keep us posted.

[rodbolt17]

no bailing wire here on the coast. we use duct tape and net mending twine.

[SeaDawg3]

don`t waste your time with racors, to many issues. the yamaha mini 10 works perfectly for that 90.

another thought is to run NON ethanol fuel.