I have an 86 Formula 242 LS with a 275 hp 350 (engine was a cam upgrade from first mate) has 39 hours on it. an alpha 1. the best I've been able to get it to run is 35 to 37 mph . tried several props it came with a 16 x16 35 mph 151/2 x17 32 to35 mph 14x19 no luck all these props were aluminum . clear lake water nice weather . today we tried a merc mirage plus 15 1/2x15 sad to report 37 mph at 3900 rpm wot . any Ideas ?? I'm not one of those who think just because its a Formula it should be 55 to 60 mph bu,t is 42 to 45@ 4800 rpm wrong ?? new to site looking forward to you feed back and help

Something is definitely wrong. Sounds like your timing is way retarded or your cam is not indexed properly. Get a timing light with a dial on it. Make sure you have 32* advance at 3000 rpm. Also make sure the carburetor is opening all the way at WOT. that engine should spin 4800~5000 RPM with a 19" prop.

Did you install the cam or did someone else? What cam are you using? Was it set up "strait up" or did someone "advance" or "retard" the cam timing in an attempt to gain a torque advantage. also check the compression on all cylinders...could be that the engine was tired prior to installing the cam and the new cam exacerbated the problem.Does the Cam hve 39 hours or the engine?

the only other thing that comes to mind is that your boat is water logged and has several hundred pounds of water weighing it down...but that's not likely.

sprink58,
Thanks for your reply . Let me back up a bit . the engine is a brand new (reman) from first mate its a replacement for the 260 merc with a cam upgrade to 275 . as far as timing i have the thunderbolt IV ignition and all seems to work well its advancing as it should and the timing is correct (actually I bumped it a couple degrees to 36) think it stopped advancing at 3200 or 3600 in that range cant remember. the carb is opening all the way . I have a holley marine 600 cfm with vacuum secondaries ,kind of concerned they are not opening . but with engine running in neutral full rev they seemed to .

you should be able to spin a 19p mirage plus on that boat between 4800-5000 rpm and get into the low 50s with the boat pretty easy, I would even try a 21 mirage plus as well. I used both on my 242 when I ran the original 260/350 and the Votrec roller motor I built. What ratio alpha one drive do you have on the boat?

Holley makes a spring kit that lets you custom tailor the tip in of the vacuum secondaries based on the strength of the vacuum diaphragm spring. I think the strongest spring is the black one and that's the one that comes with the carburetor. I am with you on being dubious about whether the secondaries are opening fully...3900 RPM with some of those lower pitch props you have been running is totally out of whack.

If it were me I would find that spring kit online and start experimenting with weaker springs. That's the cheap way out and will take some time and patience to get right. Personally I'm not a fan of vacuum secondary carburetors. I have run 600 CFM Mechanical secondary carburetors on engines like yours with great success. YOU control when the secondaries open....not some spring and vacuum system.

That boat should run in the high 40's with that combination at 4800~4900 RPM and a 19" prop.

Good luck with this...you must be frustrated.

I have a 223 with a mpi 350 330hp and have a similar situation not as bad as your but still frustrating. I've only tryed a few props first was a 4blade aluminum 19p = 4300@49mph than i tryed a ss18p=45@50mph I have a 17p mirage plus on it now which turns at 4600@51mph. My motor should turn 5000rpm wot the strange thing is that all of the info that I have found on this forum and off is I should be running a 19p mirage plus which from my understanding is basically a 20p prop and it has trouble turning my 17p.I did find a pair of bearings in the upper out drive that need to be replaced because they are harder to spin than they should be. not sure if this helps but maybe something to look at.

86242ls,
ratio is the one thing I don't know....I'm the third owner of the boat and the serial # is all but gone really tough to make out .do you know if it is also stamped somewhere on the out drive as well ??I have all (or most) of the original purchase paper work and manuals on the boat but don't recall seeing any serial #s about the outdrive . will look again

sprink 58 like you I much prefer a mechanical carb, but I got a great deal on it to replace the quadrajet that was on it. it starts great idles nice and gas mileage has been good . think I might try the spring kit one sure way I have found to see if things make a difference is going from one extreme to another (strongest spring to weakest) . if that's the problem it should surely have some affect . we'll find the sweet spot later LOL

Team...just for the hell of it put the Q-Jet back on it and take it for a run. I'm betting it might run stronger!! If you get the kit...pick the middle spring and try it. If you get the secondaries opening too fast it will bog down terribly.

I have a 600 Marine DP Holley...if you were close I would come over and help you swap it out just to see.

Im gonna give it a try this Thursday or Friday . we will see what happens . thanks for your help