Ok, last year doing 78 gps with non-labbed 27 mirage plus, sent the blade to have it labbed, adjusted the timing for more hp, Jetted down a little, last year motor was new. i put drew marine shot-gun mufflers on , they do not hurt performance they say . Jetting is stock for hp 500 , and i am running a 731 cam, dart intake, . This year iam slower, i could bury the speedo at 80 plus last year, not now. HELP

Who did the lab job? could be a bad job on the prop. Also make sure you did not develope a hook from sitting on the trailer all winter. Could the hull have gotten some water in it? Is it firing on all cylinders?Is it burning oil?

Many changes at once. Anybodies guess.

One by one verify your changes. How different was the air quality from last season and now. Bad air, high temp, high humidity will make a difference too.

Sent the prop to mercury, pier propeller sent it, it was cool that day, half a tank of gas. i also went to a extended tip plug, not burning oil. Should i trim up higher with a labbed prop . i guess i have some home work to do.

All mufflers scrub some speed. Try a back to back run on the same day confirm results.

He trimmed it more and found his lost speed and then some. But is too embarrassed to post it!

john, thats not true, i just used to trim to the moon. i will see on the river,