John in Valley Forge

Yep they are woefully inaccurate above like 20mph. Some folks refer to the dial as a Dream-o-Meter.

My guage tops out at 45, but my GPS says I am doing 39.

From discussions of this topic elsewhere, I would say that variations of 5-7mph between GPS and guage is normal.

So I swapped out all the upper fuel lines to both engines (the ones that are easily accessible from above) as well as the lines to the carb on the port engine (the one that gives me trouble). I purchased new line at the local auto parts store. Automobiles all use the same ethanol gas so I figure they should be OK (anything should be better than the original lines from 1999).

To get to the carb lines you have to remove the air silencer (the thing that looks like a blanck boat bumper on the side of the engine) and the flame suppressor. I found my suppressor, which is just many layers of metal screen, to be very clogged and dirty so I cleaned it with carb cleaner spray. Did the same to the carb opening (also kinda dirty looking). Swapped out those final lines, sprayed in lots of bar spray and put it all back together. Still need to do the starboard engine later.

Tossed a few cans of Gumout into the next load of gas and ran it hard. A little smoky exhaust for a while (OK, it seems like I was generating cover for a beach landing by the marines) but it cleared up. I've not had the power surging problem since then. More so than the new lines, I think the carb cleaner was the real helper here.

I have a '98 sportster that I got earlier in the month.
How are your dash switches laid out? Mine are in two rows, on on top of the other and go:
Bilge Fan.........Bilge Pump...........Horn
Interior lights.......Nav Lights.......blank switch.

As far as accelerating at full throttle, I agree, full throttle does not make you go faster from a stop. Much better to slowly increase throttle. I can get up to plane speed (for mine about 20 mph) much easier by slowly increasing.

I suspect that "flooring" it just send extra gas that the engine just don't need and cant use. We are talking about a 15 year old motor here. No matter how good the previous owners maintenance was, they are old and are not likely to give the same outout as a brand new one.

I have a similar issue sometimes with my '98. The port engine looses power, then regains is, then looses it, then regains it. Like if you are driving in the car and tap the accelerator to the beat of the radio.

Some have suggested to me that the fuel lines (likely the original ones) are dissolving from ethanol in the gasoline. It gunks up the carb.

No idea if its correct or not, but I did find myself looking at the engine tonight, wondering how much trouble it wold be to just replace it all.

Why does everyone assume the GPS is giving a more accurate speed reading? It's calculation of speed is effected by numerous outside forces and countless calculations. The speedo in the boat or in your car is checking how fast a wheel spins.

My car GPS, as well as both of my hand held GPS units routinely give conflicting readings of speed.