1990 Yamaha 130 2 strokes surging at high RPM.... Video

[fmt2bx]

It is 1 1990 Yamaha 130 ETXD. I have had trouble for the past few weeks now. Starts ok, idle fine, when going into high rpm (5500 or so) after a minute or so it starts surging/missing.(video)
If I throttle back (4000 rpm), it runs ok. Now if at 4000 rpm for long time, it starts acting up. If I let it idle for a bit then all ok until I get to 5000 + rpm.
Compression (1,2,3,4) 130, 135,130, 130
Running on ethanol free fuel 87 octane
prop 19"
Boat 19' Byliner capri.

Video here--------> https://youtu.be/t8cj_U_cvXU




-Cleaned both carbs 3 times now. Completely disassembled and cleaned.
-Change fuel pump
-Changed ALL fuel hoses (Boat and motor)
- Bypassed the fuel disconnect
-Changed primer bulb
-Ran from external tank
- open gas cap for extra venting
-Changed spark plugs twice
-Replaced fuel strainer (Motor side)
-Bypassed external fuel filter
- New stator
-New pulser
-New coils
- New plug wires and connectors
-New pack
-New rectifier
- Replaced impeller
-Replaced T stats
- Checked Alarm buzzer for oil and over temp, all ok

- Did a seafoam cleaning
- Battery charging ok
- Tach working and not erratic
- Checked and cleaned all ground connection
- checked all electrical wire connectors , looked ok


In the video, there is a bit about checking the fuel pump output at cranking, I do not have the equipment to check while running, don't know if output is normal. Was hoping someone could tell me.


I opened the control box and checked the ignition and emergency stop switches. Connectors seemed ok but didn't do a complete tear down. Was looking for obvious signs of problems.

I haven't looked into the oil system yet or timing.

I am running pretty much out of ideas of where this could come from. Fuel or ignition and what could cause that after all that was done so far.

I 'd appreciate very much any inputs.

Thank you.

PS: I d like to apologize in advance if I forgot to list some other things that were done. It has been a full time job trying to get this to run .

 

[ClassicAQ]

According to experienced marine mechanics, 90% of the time when an outboard is experiencing problems it's related to the fuel system. So that's where I'd focus the majority of your troubleshooting. Looks as though you've addressed the entire fuel system though, either replacing parts are cleaning. I'm curious to learn the extent of your carb cleaning. In particular, when you disassembled the carbs did you also pull out all jets, soak, and clean orifices of each one?

You want to be able to hold each jet up to light and see right through it. It only takes fractions of a millimeter of debris to clog a jet. If this occurs in one of your high speed jets I would expect you'd experience what you've described. I mention this cleaning of jets because many boat owners who clean their own carbs do not pull jets. Yet cleaning the carbs and not pulling the jets is just a waste of labor time. Spraying carb cleaner into the opening of a seated jet will not do the job, despite what some believe.

When you're experiencing the surging, have you wrapped your hand around the primer bulb? Wondering if fuel continues to flow through bulb or if it collapses above 5k rpms.

 

[fmt2bx]

Hi classicAQ

took both carbs totally apart, clean all jets and dry clean with compressed air. I understand your question, I have been reading plenty of post where the individual just sprayed carb with cleaner. Not here and actually did it 3 times. I was determined that it was a fuel issue. even put a gage at output of fuel pump and reading 5-6 psi at all time, even during the misses.

Changed fuel pump as well and prime bulb and squirt fuel from spray bottle (not easy when the miss is so short) into each carb but no joy thee either.
I haven't noticed the primer collapsing though.

It really looks like it is an electrical issue. I started to troubleshoot by removing some electrical devices such as the rpm gage from the loop. See if something is causing an electrical surge.

 

[Doh]

That fuel pump, doesn't seem to be pumping enough. Is the bulb soft when it is dying? Sucked in? Put some clear line on it and check for air bubbles. Try a run without the shroud.

 

[fmt2bx]

All great points, thank you. I had a pressure gage at the output of pump and was reading 5-6 psi, which is within specs.

Found the issue. at last, after troubleshooting the fuel system for days... Bad (new) coil on #3 cyl. !!! Few days ago, I just had it with this problem. Went on the lake, WOT, started to miss/surge after 2 minutes ( as usual), kept going for a little bit then turned off the ignition while at WOT. No idea if this is bad for motor or not but I wanted to check plugs while this was happening. Here is picture of #3.

Changed plugs, no improvement, changed coil and fixed it.

FYI: The faulty coil was brand new and Ohms checking just fine. I guess when it heats up it starts acting up.