I just bought this rig used its a 2000 GD 27hp Kohler LT on a GD 18' boat. She ran about 15 mph at 3100 rpm. Does that sound right to you guys? By the way I'm about 270 and my buddy is 300 lbs give or take. Also she choked off once and twice she bogged down but I turned down the throttle to idle and it caught back up like nothing was wrong. Any thoughts on this would be nice. Thanks

First - which hull do you have there are several different widths and bottom profiles.

Round chine like the 18x38 and 18x44 sit lower and are a tad slower with a load like you two big fellers. The 18x48 is a tapered chine and would do a bit better with that loading.

My GDSD 16x48 with stock 23hp did 21mph with a 220lb driver and 18mph with a second 220lb passenger - but add a kid at 100lb and only about 15mph.

Your best investment would likely be a new prop - take your old one with you and compare the diameter and blade width to a new prop of the same pitch - based on your RPM stay at same pitch or go down 1 pitch to get more torque and speed under loads like the two of ya'll - and yer gear.

Each 1" pitch change is drastic on these motors and so is prop condition a 1/4" blade loss due to wear is a performance killer.

PS - 90 percent of motor issues are fuel quality and delivery related - use 1/4" line not 3/8" and replace filters, fittings, and put a good bulb on - I like the Yamaha bulb with small tips within 3 feet of the tank - you can have 20 foot of hose back to the motor from there. Gresae it and run some high octane premium - see it if lines out in a few hours of hard running.

Thanks for the advice I think its the 18 x 56. The tank is in the front of the boat and only bulb i saw was by motor. So I should get another bulb for front then. How does one know when the prop is shot?

That ain't bad from a long tail.