Yamaha 250ETXD - 1990 Low Power Only

[Aquanut2]

Have been trying to trouble shoot a problem with this engine it will not go above 1900 rpm and power boat up on a plane. It gets up to 2300max but reduces right back down to 1900, seems to go into protect mode. Blinkey does not currently flash any errors (just one flash).

It did have errors 10 and 4 because the plastic TrimTilt arm broke off the sender but I turned it with pliers to show normal trim on the gauge and the errors went away.
I've also replaced the knock sensor, temp sensor, water pump because I had a temp warning on the RPM gauge but it's not flashing/buzzing any more.

If I disconnect the knock sensor rpms will go up to ~ 2300 without reducing back down to 1900 and once went up to full power ~ 4900 getting boat on plane at WOT, but never happened again so I think fuel carbs are ok.

Right now the Temp oil gauge has a solid triangle above the green oil symbol not sure if this is normal or an error.

Have 16 family members over for the holiday weaken Strippers are running and we can't get out to fish.
Any help/suggestions are most welcome

[Aquanut2]

Compression is good

Did a compression test all 6 cylinders are the same at ~105 psi

[rodbolt17]

most likely ,dirty fuel system.

but do check the charge coil voltage. there were some issues with the early stators.

[Aquanut2]

Thanks RodBolt
Ran the motor off a portable tank and still have same problem rpms drops back down to 1900. I have the shop manual and checked the resistance of the primary coil and it's within range Spec is Black- Black/White 0.179-0.242Ω
But the resistance of the secondary coil (plug wire to ground) is out of spec
Black -Secondary lead should be 2. 73-3.69 kΩ but reads 8.5kΩ

The blinkey does not show any faults but one time flashed code 11 pulser coli while starting, I could not get this to repeat. Tested the resistance across all the white wires on pulser and reads within spec 294-398Ω

Disconnected the knock sensor motor will get to 2300 rpms without dropping to 1900 but does not have normal power at that speed.
One time while testing it did get up to 4900 full power but after stopping it went back to limp mode.

Ended up buying a used CDI with 6 coils off ebay for a good price and hope it will help will post results back here this weekend. Let me know if there is anything else I can check out.
Thanks
Mike

[rodbolt17]

13 is pulser, 11 is secret.
however I DO know what code 11 is.

and I know code 11 isn't your issue.

and your going to have an ECU and 6 spare coils.

[Aquanut2]

Nothing like having a bunch of spare parts!

Ok not sure where to look next then nothing like having a pile of extra parts!
I'll give the new ones a try anyway since it's easy to change them out.
The stator is a but more difficult so it's off to the shop next.

Thanks for your help
Mike

[Aquanut2]

In My Case it Was the ECU

Just wanted to post a follow up that replacing the ECU did get the motor back up to full RPM and out of the "Guardian Mode" so the whole summer isn't a loss!
One thing I did not share was the Oil Speed Temp Fuel gauge was dead as well this year so I am wondering if a surge took them both out.

Rod Bolt was right about the fuel though the squeeze bulb had a ball that would stick sometimes which I couldn't trouble shoot until I could pull more fuel at WOT and watch it go flat.