carb. 500hp's grabed the wrong fuel hose and i am running 1/2 reg. 1/2 prem. in boat, lost about 500 rpms and a bunch of speed. have only run boat 3 other times and never had an issue until the reg gas that i pun in by mistake. could this have been the problem or do i need to keep looking?

Should not make a difference. The Octane does not effect horse power but it allows you to run higher comperssion engines with out detonation thus making more horse power.Otto

Better look somewhere else I have modified 500's a tad bit more compression and different cams and run 89 with 0 problems. I would look for water in the fuel or other related problems (clogged filter).

Are the rpm's down in both engines or just one?

more on the port but both are down

I noticed the same thing on my engines when I took the boat for a spin early this spring (end of March). I am down about 200-300rpm as compared to last fall with the same fuel that was in it before and using the same props. I put the boat away without touching the engines other than fogging them with a specially formulated fogging oil that is in an aerosol can. The only thing I can think of is that perhaps because I put the boat away last fall in storage withOUT loosening the rocker arms to relieve the tension on the valve springs which can weaken the valve springs over a period of time-----it sat that way over the winter. I ran the boat last fall with a fresh valve job on both engines, therefore they only have about ONE HOUR of running time on the engines with the new valve job and the engines only have about 50 hours total. It's the only logical reason I can come up with!