I have a 23hp GD surface drive that I need to have checked out. Anyone knows of someone in the Thibodaux/Houma Louisiiana area that I can bring it to?

engine or lower unit?

Bring it to degates on barrel street in Houma

prop wear?
Hull condition?

Ran it today me, one sone (160lbs) and gear 20.5-20.8..............seems about right. Should one more person slow me down that much? Hull is fine. What should I look for when looking at the prop?

If its on a smaller hull then the added weight may slow it down a good bit, prop wear can make a big difference in speed also. You need to find out the props original size and measure the current size from blade tip to blade tip, if its worn a half inch or more a new one may be in order.

What is the engine doing that makes you think something is wrong with it?

Last year loaded with me, two sons and gear we would run 17.5 to 17.8. Went out last week and ran only 13.0 to 14.0. Before the season I changed the plugs, oil, filter and fuel filter. It's the original 2 blade prop that came with it from go devil............measures 11 1/4"

How much have your son's grown since last year? You say the hull is fine, but sometimes it doesn't take much. Look for any (even small) indentations in the hull, especially near the transom, they can rob speed.

Take a look at your valve lash. If your getting rpm's out of water but not in the water, your valves could be out of tolerance. Could also be from hooks in the hull, prop, or added weight from the boy's growing, or a number of other things.

I'll check the hull out real close. My oldest hasn't grown..........he's big but hasn't grown since last year, my youngest may have added 10 lbs.. A friend who's has a boat shop will check it out when he gets a chance but he's currently tied up with BP

Yea measurement on that prop is 11 1/4 brand new

Nobody ever asked what your rpm's are, out of water and in the water? Do you have a tach?

I'd take a look at your valves either way, certainly due for a check. It's quick and painless. There's a good video on youtube that shows you how to do it if you aren't sure.