I cant seem to get any more than 3800 rpms out of my modded motor. I had the cam shaft & heads changed, and the timing advanced. I test ran the engine and could only get 3800 max rpms. I then gutted my stock muffler thinking that this would help but made absolutely no difference. I just test ran it again and could get no more than 3800 rpms. In neutrol, it will turn up to 4350. Any suggestions?

What were you getting before you modded it?

What size and model boat do you have it on?

You sure you're trimmed right (i.e. the transom angle is compatable with the motor?- stupid question but 3800 doesn't sound right). Can you trim it up off the water (where the handle pushes into you?)

It used to turn 4200 stock with the 11x9 prop. The engine is on a 16X48" go-devil surface drive boat.

If i trim it all the way up i think it hit 3900 rpm.

did they re jet the carb?

Not that i know of. I dont think they did because they never mentioned it.

I am no mechanic, but I think that most of the people with heads and cam ATLEAST have a rejetted stock carb and gutted exaust. I think re jetting the carb adds your top end. But I am sure someone will correct me if I am wrong.

I have tried that but i lose speed. I can trim it almost all the way out of the water also.

Last year I picked up a new 17x54 GTB and I could not get the rpm's over 4000,moved the pin to the middle hole and my rpm's came back to normal.It still runs fine in the bottom hole but for top end performance its better in the middle,but when you get in a bind you will want the pin in the bottom hole to be able to grind out.With my motor anything over 4300 and I start to loose performance.If Hoyt did your modds he rejetted your carb.

Something is up if you are running the same prop, take Delta up on his offer.

Re-jetting the carb will not make that much difference in RPM, if it was lean you would probably be running higher speed but producing high heat (to much) in the cylinders with the added compression.

Problem has been fixed. Me and Delta went ride this morning and we tried a few things. He had some spare props that we tested and found that with a worn out big prop my engine ran awesome. With my new prop on the motor i could only get 29-29.5 mph. We put on his prop (same exact prop but worn a little) i gained 1-1.5 mph. We then put the engine on the middle hole and gained even more. After all this it ran a constant 33 mph and at one point hit 34 mph. Now this engine is running like it should. Dont know what rpm i'm turning because my tach. quit working. But thanks to everyone and especially Delta for helping me out. No i really have an engine!!

Cool

I thought that I read that he was running a GDSD