2007 8hp 4 stroke will not run high RPM

Dad's 2007 8hp 4 stroke Tohatsu outboard running on a 10' RIB. He has been having problems with the motor for two years of infrequent use. He said he got bad gas once and the motor hasn't been the same since. He indicated there was water in the gas but I forgot how he figured that out.

Originally there were idle problems, then starting problems, and WOT problems when we did get it running. I replaced one of the two plugs (it was all I had at the time) but they didn't look bad either. No change. Then I took the motor home and removed, disassembled and dipped the carb. I replaced the fuel line from pump to carb and replaced the fuel filter. I replaced the crankcase breather line as it got caught in the flywheel at some point. I also removed the fuel pump and cleaned it but didn't dip it. I found more corrosion than I expected in an engine with less than 20 hours on it (carb and pump).

Reassembled and ran it in a bucket. Idled great, WOT in neutral great. Ran it up in gear with earmuffs on a hose (no bucket, no load) and it ran fine. Starts easy, choke runs right. Hauled it down to the boat, starts easy, idles easy, but dies as soon as you open it up.

Also note that opening it up on a 10' RIB means a huge angle change as it starts to get on plane, but dies before it gets there.

I'm thinking fuel pump rebuild kit next, replace the other plug, any other ideas?

You may be in warranty. What does your dealer say?

What is the crankcase oil level? What prop pitch, and what boat (are you correctly propped)? That motor is a bit on the smallish side for most 310 RIB's.

If there is corrosion inside the aluminum fuel passages, you did in fact get a load of water in the fuel. That oxidation could well have rendered you carb and/or pump junk. Keep in mind that bad fuel is not covered by warranty.

Thanks for the reply. When new, the prop and motor were perfect for the 10' inflatable. Everything is stock. Too much pain to take it to a dealer to hear it isn't under warranty.

Crankcase is full, top of the range when I checked.

So, what order would you go? I am thinking:

(1) plugs
(2) fuel pump rebuild kit (can't find part numbers for a kit)
(3) carb rebuild kit
(4) new fuel pump
(5) maybe supply line to the external tank

one at a time, in that order. Carb has been dipped already. Is this order what you would proceed? Am I missing any?

Probably still a carb issue, since it is stumbling coming off idle. But still could be almost anything. If you "ran out of gas" after getting up to high speed, I would lean towards a fuel delivery issue, but that doesn't seem to be your symptom... so fuel pump, etc., is probably OK. Check the condition of the DCPR6E plugs before you throw new ones at the motor. They are probably good, and likely don't need changed. You should be OK at FULL on the dipstick, but I typically don't fill new (under 10 hours) motors that far, because if they make any oil at all, they will be over-full, and will have crankcase pressure problems (including high speed and idle issues). You can always let a couple of ounces out to lower the level to below the FULL mark. That motor has a 3-yr warranty, so check the receipt for the date.