Would somone please tell me what would be the cause of a motor not running all the way up to it's max r.p.m. My motor is a freshly re-built 502 mag MPI. I know this motor should turn a little over 5000 rpm @ full throttle, but it will not go beyond 4700 & that with tabs all the way up & drive trimed up.My tech sheet that I got with this boat showed it turned 5050 R.P.M. Could the builder have done something w/the timing not let the motor rev as high to be safe?

Check for a busted spark plug on the installing of your exhaust.Just had a customer have it happen to him.

Thats one thing, could be any number of things from a broken plug to mixed plug wires to a cam installed a tooth off thats why always better to know the actual person doing the work, is it the lead tech or just an apprentice

ps... even lead techs make mistakes they just have the exp to check them before anyone knows it and they know short cuts usually end up being long cuts ....

thats why I always double and triple check my work then if someone else thats qualified is around I ask them to check me I dont belive there is any excuse for a customer having a problem with anything I do

and anyone who says they dont make mistakes is a liar

Are you over propped?

Could it still be a plug, even if the motor idles very smoothly and it runs strong? The motor runs good & sounds good but it just does'nt top out to max r.p.m. As far as being over proped I would'nt think so it's the same prop that it ran 70 mph @ 5050 r.p.m (according to the performance sheet)

That tech sheet may have been taken in "ideal" conditions. Cool air, 20 gallons of fuel, just the driver on board, and a perfect 1 foot chop with a 30mph tail wind. You may not have any problems at all.