I just purchased a 92 mirage intruder with a mpi 502 when I bought it I recieved 2 props with it one is a 4 blade 24p and the other is a 3 blade 23p prop I took the boat out with the 4 blAde and trimmed out was only getting 58 mph at 4500rpms it seams like it should have allot more. I'm not sure how to find out the out drive ratio but when I bought the boat the guy said the boat will do 72mph and to run the 4 blade prop I was wondering if any one had any suggestions on what to try? The boat has been sitting for two years

Sitting 2 years?-- Not a good thing.

I'm not an expert but I would say it probably is bad fuel - stale gas- almost varnish- Worse thing for an engine is for it to set an extended period without running. I would suggest a good cleaner run thru the engine and change ALL of the fluids. After this I'd also include plugs maybe even wires distributor cap etc. Again, I'm not an expert but the rpm's for this "class" of engine seem a little low-- We have Cobalt 226 with a 7.4 mpi and it turns about 4500- 4600 WOT and top speed is 63 mph. You are in a much higher performance boat and with that engine that sucker should scream!

good luck

3pointstar

Fuel filter too! You'd **** if you knew how bad a bad fuel filter and old gas can make a good engine run like crap.

I have a 21 superboat with a 502 bravo 1 1.5. Best speed has been with a mirage non plus 27. 87.1 on the rev limiter. Hope that helps

Yes you have a problem as to where that i cannot say, I have a 87 with a tired 330 hp 454 1.47 gear ration turning a 23 4 blade to 55 @ 4000. Time to freshen up that 502..have you done a leak down test, might be a good ideal before you throw a bunch of good money around.

Yeah with a 21 degree deadrise and a 502 you should be high 60's, maybe knocking on 70(if it's running to potential). My dads 217 intruder with a 260 merc does 53-54mph and it's stock besides Stainless Marine Exhaust and Mirage 3 blade prop.

Definitely take the above advice and perform a compression check. If the numbers look good, change all fluids and tune up including evaluation and possible rebuild of the carburetor. For an engine that's sat for that amount of time id say it's time for a valve spring refresh here in the near future. Cheap insurance considering the alternatives.. Btw cool boat and good luck!