Did a few laps around the lake, all was fine, then suddenly wont go over 30mph. I owned a Kawasaki previously and I remember reading in the manual that an overtemp sensor would limit the RPMs if it got too hot. I am wondering if these skis have similar overheat sensors, i bought this ski a few months ago but the previous owner didnt have the manual for it. Basically i need guidance as to where to begin my diagnosis. Thanks!

go online to yamaha-motor.com and you can view the owners manual for free on the web page and even download it.

check the cat con [part#55] it often breaks up and drops lower in the exhaust, clogging the stinger. riva has a replacement called a D plate. god investment and cools off engine temp. also will need temp sensor chip if u do this fix.see pic!

or you may have damaged a piston / cylinder

to do a compression check

- disconnect ignition wires

- remove all 3 spark plugs

- install compression gauge in each cylinder 1 at a time

- hold throttle fully open

- turn motor using the starter

all 3 cylinders should have a similar reading (around 110 / 120)

cat con has been eliminated with a D plate, compression is 130 130 120. Is there a limp mode function on this boat?

the tip of the spark plug on 1 of the cyls had metal junk stuck to it, like little ball bearings... looks like its going to need a rebuild on that one cyl BTW its got a RIVA head on it, I am now thinking the previous owner may not have had the carbs setup properly, what i dont understand is it ran fine the 1st time out, and the 2nd time out it happened

Ran fine the first time so you need to see what changed. Did you change the premix? Pull the engine, split the case and clean out the seals/bearings. IMHO

opened up the head and the pistons look beat, the only thing different is that I used Yamalube 2R oil instead of 2W as recommened, and the previous owner said he used to use Amsoil Interceptor

Well, maybe you will find the culprit when you pull the engine. It is not a bad job. I purchased a used cylinder and let riva rework it. They did a good job. The only problem was they did not run a tap in the threaded holes. No big deal but I had everything coated in sealant / lock tight. Then figured out the bolt holes all had the chrome in them. Had to clean everything and tap holes. For your piece of mind don't try just doing the one cyl.