Rpms Fluctuating

Have twin OB"S Ocean Pros

Have twin OB"S Ocean Pros about 800 hours 1997 vintage- i continue to have perplexing problems this summer last two days ran the boat all over the place at a comfrtable 3800 rpms-20 knots I was finishing up the day yesterday with some drifting I would only use one engine to move me around- when I went to get up on a plane the port engine's rpms were fluctuating wildly 3200-4000 rpms- the starboard engine was not fluctuating like that but I believe the speed was compromised because of the other engine. I checked the basics out side the engines to see if I could figure something out no luck- nothing obvious to me- I even switched fuel tanks still the same symptoms - no obvious overheating or any thing I could see any ideas? Gary Korbel

"A bit complicated on theese e

"A bit complicated on theese engines, but could You run a fuel pressure check?"

Ran the boat yesterday and did

Ran the boat yesterday and did 2 things one put more fuel in main tank to 1/2 full ( I had run down to about a 1/4 on the main am I loosening uop some junk on the tank as I run from over a 1/2 to 1/4 and opened up and took off the filler fuel cap on the main tank (some one suggested that here) - boat ran a good deal better the rpms fluctuated less at higher rpms about 4000 rpms -the minutre I put the fuel cap back on there was more of a fluctuation in the rpms does that make sense?