Formula 242 not up to snuff.
 

My buddy just bought a 1986 242 with a 454 mag and bravo drive. The motor is what I suspect to be a gen V. The fuel pump is on the sea pump. He is only getting 48mph at 4100 rpm WOT. I had a 420hp with bravo drive in my 86 242, I got 62mph at 5000. I assumed his boat with 365hp should get 57mph or so.
His setup:
365hp
Bravo 1.5 ratio
21p Mirage prop
48mph @ 4100rpm

He verified that all 4 barrels of the carb were all the way open. What else should be checked?

How old is his fuel ? I had a similar problem with my boat until I ran out most of the old gas. Filled up with 93 octane...problem solved.

Seems simple but worth a look.

I am hoping a tune up will take care of things. I suggested a new fuel filter, cap/rotors, wires, and plugs. It seems to run well right up to 4100, then more throttle doesn't yield more rpm.

Check timing , make sure its getting full advance. Good Luck!!!

I was thinking that too. What should a 454mag be all in? 34*?

It is rare that you need to replace the wires on boats. See if they are flexible and not worn through. Check timing,

I hope it's minor. My friend is not up for a new motor.

If it was running good when he put it away last year and their is no miss-fire...then the only thing that could have changed while it was sitting up is gasoline quality. If it has 12 month old pump grade ethanol in the tank I would be very suspicious of it's quality.

All of the other suspects, plugs, filters, caps, rotors, wires, etc don't go bad (well maybe a coil froze...but it wouldn't run at all in that case) during lay up.

If there's a 1/4 tank or less...add a bottle of gasoline additive and fill it up with 90 octane Non Ethanol and see how it runs after a few hours.

+2:)

Check the basics as stated. Other things to check would be compression, cylinder leak test. If the engine has been run in salt water, I would do a cooling system pressure test to see if you are getting rust-thru around the valve guides or elsewhere.

Also, how's the structure of the boat? if it is wet/rotting, then the boat would weight a lot more, which can be the culprit.

I ran into a very similar issue and it ended up being a hairline crack on one of my spark plugs.

I know the boat is solid. The previous owner replaced all the stringers and transom. This weekend we are going to go through it better.

I had a 85 272, throttle cables were stretched. This kept carbs from going wide open.

[I]s this his first boat ? Or first boat with trim ?

He had a 17' sunbird with 130hp alpha one. He ran that last year. This is his first performance boat. I am going to visit him this weekend. I am gonna run the crap out of it for him.

He said that's trimmed all the way up. I wonder if his trim limit switch is set real low. I'm gonna check into that. Maybe bump the trailer button while running it.

Solved!!! Choke was not opening 100%. That would not allow the secondaries to open at all.

Not Solved! (My boat)....Secondaries are opening and getting more RPM now but still wasn't able to hit 50....49 MPH@4800, trimmed about 3/4 (seemed like the best run, more trim and she dogged out) tabs up.

Fuel still maybe? Sittin about 1/2 tank of 1 yr old + go-go juice...

Timing was perfect (10 degrees)....79formula calculated me at 19% prop slip....HELP

How is the bottom, clean and smooth, no bottom paint? What is the diameter of that prop?

No bottom paint, smooth as a baby's ass however I did discover today that I have the Formula "hook". My buddy has had his removed so I think this is costing me some top end.

Running a 21p. Going to try a 21 plus in the next few weeks. I'm told this should yield a few mph

I would suggest a 540 and some headers.then you wont have to mess with the hook.:party-smiley-004: