Bad Fuel Pump??

[workinpr0gress]

I would start with an original shop manual, multimeter, and a compression guage. It could be a lot of things really. Many a high speed problem can be attributed to an electrical problem like a timer base, rect., power pack, stator, temp... etc. I have seen coil packs do something very similar at higher rpms also, from old wires arcing or the pack being weak, or corrosion. If it is ultimately a fuel problem then I would take it back to the person who did the carbs. The float height is a straight forward thing. All that said, it's pretty easy to pick up a piece of crud in the needle and seat or a jet. If it goes on for a while it can score the cylinder a little and it will read a good comp.# but at higher rpm under load it can wipe the cylinder wall clean when that piston temp comes up. Especially the top two cylinders.

It's a tedious job of process of elimination for a broad problem like you have but it'll be like a checkup for your motor.
Good luck

[77SceptreOB]

I've replaced or rebuilt just about every fuel related component. So I doubt that is the problem.

Compression was checked and was good. 130 psi max, 122 min. almost equal side vs. side at the same cylinder elevation. the lower 2 were 122 (left) and 124 (right). middle 128/126 and top 129/130.

Electrical, now that a different story. I believe that is where the problem lies. This was a saltwater motor and no parts, except sparkplugs, have been replaced.

Any ideas on how and where to start troubleshooting the electrical system. Preferably with instruments and cheaper parts first. LOL.

[workinpr0gress]

I've replaced or rebuilt just about every fuel related component. So I doubt that is the problem.

Compression was checked and was good. 130 psi max, 122 min. almost equal side vs. side at the same cylinder elevation. the lower 2 were 122 (left) and 124 (right). middle 128/126 and top 129/130.

Electrical, now that a different story. I believe that is where the problem lies. This was a saltwater motor and no parts, except sparkplugs, have been replaced.

Any ideas on how and where to start troubleshooting the electrical system. Preferably with instruments and cheaper parts first. LOL.

The oem shop manual for that motor. Ebay. At this point if you have a local marina guy who dealt those motors he'd probably let you borrow the manual for a good while. The "assumed knowledge" terminology sometimes is a pain with oem manuals....get yourself a haynes/chilton also and you will be set to tackle almost any problem that motor can give you. Get yourself some beer and a friend for the electrical stuff or get yourself test harness. Bring your patience in abundance. Don't skip anything if anything do it thrice and log every number. The fact you belive it might be a corrosion problem means maybe clean everything up and lubriplate, grease. Check for pins that are broken off inside the boots. They have been my nemesis numerous times their crimped shape holds them in place when they snap right behind the crimp. Talk about intermittent.

[gss036]

If you can't figure it out, go over to the Iboats forum and post. There is a master Yamaha mechanic that hangs out there and he is very good at trying to help out with problems. He lives is Kittyhawk N.C. and goes by Rodbolt.