TPS or EMM or both

[Ktibb]

@HiPeRcO and @K447, First time post and I've read through a number of your responses, but haven't seen a similar scenario, so I thought I'd ask.
I've owned the 2003 Virage I for 3 seasons now and the first two seasons, we had no issues with the ski.
This year, first time on the water, the ski started and ran no problem, but at full throttle, the ski seems to only want to run at 3/4 rpm. I can reach between the throttle lever and the handle and pull extra tension on the throttle cable, while underway, and eek out another 500 rpm out of her, but that's still not 100%.
In your opinion, do you think I need to start at the TPS or have the EMM looked at or both?
I have not done any troubleshooting at this point, other than put extra tension on the throttle cable while underway.

Thanks in advance.

[Myself]

Was it winterized CORRECTLY, and COMPLETELY? Cause it sounds like symptoms of old ethanol fuel that's gone bad.

I'd start with siphoning out the gas, put fresh back in, and new spark plugs.

[K447]

Adjust the throttle cable slack to be correct, then retest the on-water power range.

Throttle cable should have just a hair of slack at idle position. Look at the throttle body shaft front while adjusting the cable slack. You want a tiny bit of handlebar throttle lever motion before the throttle shaft on the engine begins to turn.

With the handlebar lever clamped tight to the handlebar the throttle shaft should be at maximum rotation, against the mechanical stop. Turing the throttle shaft by hand (while the handlebar lever is fully squeezed) should not move the throttle shaft any further.

Confirm there is a little slack at idle and full shaft rotation at WOT lever squeeze.

Throttle cable slack adjuster is a few inches along the throttle cable, below and forward of the throttle cable attachment to the engine. There should be a locknut for the cable adjustment. Loosen locknut, then turn cable sheath to adjust length.

Also check that the TPS sensor on the back side of the throttle shaft is snugly in correct position. Bolts not loose, TPS body not cracked.

Then water test.

[Ktibb]

@K447 Thank you. On the water last time, I did all the throttle cable slack adjuster changes, but didn't think to check the mechanical stop and full rotation at full throttle. I'll go check that now.

@Myself, Yes.

Oh, and I just pulled the plugs and one has clearly more carbon build up on it than the other. I'll replace these and monitor that difference and the cylinder head temps to make sure they are ~the same next time.

The plugs that were in it from previous owner are an Autolite Platinum APP 5224 gapped .036. Thoughts?

[HiPeRcO]

Spark plugs must be NGK PZFR6H or CHAMPION QC10PEP only. NOTHING ELSE WILL WORK

[Myself]

I literally just removed a set of the Autolite APP5224 plugs from a customer ski that was having trouble starting and idling.