Is this possible?150hp for my 16' boat?

[carmex234]

Looking for pointers on a powerhead swap. I have a 76' 115 inline merc, and the tooth fairy left me a fully rebuilt longblock 76' 150 inline ser#3203807. What all is needed to make this trade go as planned? From what i understand, the 150 has differant porting,and the hi/lo speed jetting is diferant. Carbs are same type A. Will the stator, and switch box,distribtor all work transferd onto the 150hp? I have a small light 16' tidecraft v hull and im thinking 150hp is gona make this rascal **** n get! What size prop could i turn with the 150hp? Or is my quest for speed gonna put me in th hospital? Any guess as to just how fast we are talking about? Im thinking i could turn at least a 26p if not more.

[Raceman]

It's a direct bolt on............. about as simple a swap as you could ask for. I'm not even sure that the jettin' is different, but somebody'll probably jump in and tell you. You need to run Premium gas, good oil at NO LEANER than 40:1 (I run 32:1 in all my inlines, other Mercs too for that matter) set the timing at 21º, keep a good water pump in it and prop it to turn no less than 5800 RPM's. 6K won't hurt it.

As far as speed increase, it won't be night and day, but I'd guess 6 MPH. Since the 1150 was a torque motor and you didn't need to turn it as hard as the 1500, the same pitch may work. If not try an extra 2" next. Again, it's important not to over pitch and lug these engines. They'll burn pistons if you do.

I'm not familiar with the TideCraft. but a 26 pitch wheel at 10% slip and with the 2:1 gear ratio of your engine would run a boat 64.2 MPH. Don't forget that most speedos are off 10% or more until you get into the high dollar stuff, so get a GPS and don't fool yourself when you're messin' with your setup.

[carmex234]

Yes, looks very straight forward. Should i look around for a junk 150 and get the carbs off it,and get every other part from the 115? Im intriuged, how fast could i get this boat to move?

[crazy horse]

You'll need a set of .080 jets for the carbs and if your carbs are late model then you want to remove the little brass jet at the top of the float bowl. My 15 ft. boat has had 150+ hp. on it for 30 years so I don't think 150 hp. would be to much for a 16 ft. boat:D.

[Raceman]

My guess is that Grigg (Jeff G) jumps in and helps with the jetting question. If he doesn't I'll pull the bowl off one of my 1500 carbs in the morning and tell you what's in em. In any case, it's not worth changing carbs just for the main jets. The venturi size is definately the same.

[Raceman]

One other thought: be sure and get a new base gasket. The 73 and newer inlines are prone to the gasket leaking or burning out between the two halves of the exhaust outlet at the bottom of the powerhead. This can make the boats lazy gettin' on top.

You also need to be sure that you have the year model stuff you think you do. I see engines on E Bay all the time listed as the wrong year models. If any of your stuff is pre 72 it won't interchange with anything later, and the 72 1150 was different from the 73 and newer also.

[Raceman]

Like I said, "My guess is that Crazy Hor jumps in and helps with the jetting question.":D :D

[SAMMY CORLEY]

My 150xs had 82 jets to start left a lot better wit 78.5 but was on da edge.





Sammy in S.C.

[carmex234]

I just so happened to hav 3 -.080 from a previous victm. Is it really that simple? Do yall think the swap is even worth it? This 115 runs tight and strong like other 115 i hav seen run. Im okay on years both blocks are 76'.

[Raceman]

I think you'll find it well worth it and yes, it really is that simple. 'Course swapping an inline powerhead is time consuming, but you've got everything you need right there.

Do you have a flywheel puller? Don't attempt it without a Merc specific tool.

[Dave S]

I had a 150 and went up one jet size and the plugs ran rich on 2-4=6 and lean on 1-3-5 Maybe because I was useing a T2X Exhaust housing. Best bet is to use jets that came in the carbs they came in. Or better said use the carbs the jets came in and off an old 150. When you put it all back together, the timing belt is hard to line up so look at it before you take it apart. The arrow on the pully needs to be just a littel advanced. What I do is put it on and not put the plate on, full advance spark check, if it is way off, try one tooth + or- ;) Just in case you haven't been there before. Now a question for everyone, has anyone seen small plastic balls on top of the idle emulson tube? that is where the idle screw goes thru, or better said on top??? I pulled a 150 carb apart and one had a small ball. It seemed to have a small recess in the emulson tube, where the gas goes up to the idle jet area. If your not looking for this small ball, it will get lost and you would never know it was ever there. Thanks all.:)

[carmex234]

Ya, i had to break down a few years ago and buy some merc tools, fw puller,spanner wrench. Cant operate without them so worth the one time investment. I have a ? on carbs. In my seloc manual,and other sources i see type A carbs with actal choke plates, inside he barrel. What yeard did they start this? I think mercs choke shutter is a joke, and doesnt do what a choke does. That is assuming actual barrel choke A carb works any better.

And while im at it id like to yank he exhaust tuner for that merc ''tone''. Seloc doesnt explain remoal, and i dont fully understand how to do it. So with the powerhead removed,what next? Is the ex can pulled out from th bottom? Is it bolted down or spot welded in there? Without the can in place, does th excess heat harm anything? Discoloring th mid paint sure but how abot the waterpump houseing.

Gentleman, its been a pleasure.

[crazy horse]

To get to the liner your going to have to remove the ex. adapter. First you need to remove the plate below the powerhead ( if the powerhead is already off). When you lift that off you should see the top motor mounts you'll need to pull them out and then remove all the bolts on the adapter, These bolts can a pain to remove. When you pull the adapter the liner will be right below it, just lift it out. Make sure you remove the small liner support plate and the seal from the gearcase where the liner set in. When you do this job you should drop in solid mounts while you have it apart. I think thats it, I have not done one for a couple of years. Mine liner has been out sence I set up my one center section for a speedmaster. I run my standard case with the plastic pump cover and haven't had any problems with it. My center section still looks good and the paint on it is 28 years old.

[Raceman]

"And while im at it id like to yank he exhaust tuner for that merc ''tone''. Seloc doesnt explain remoal, and i dont fully understand how to do it. So with the powerhead removed,what next? Is the ex can pulled out from th bottom? "

Are you talkin' about removing the can or the tuner? I'm assuming you mean can. I don't think it'll make a substantial difference in sound It's not spot welded in, but is much larger at the top, so it can't be pulled out through the bottom. Like Crazy said, the bolts in the two upper plates that sandwich the upper mounts can be almost impossible to get out in one piece and there's no way to get heat on em. If you wring em off you'll create yourself a nightmare that you wish you hadn't. If it's just noise you want you can drill a couple of holes on each side of the gearcase above the cavitation plate and into the exhaust can, which is lower than the bottom of the mid on an inline. You probably should drop the gearcase and look first so you can get the holes in exactly the right place. None of this exhaust stuff, whether removing the can or drilling the holes is gonna help performance, except for maybe helpin the boat jump on top, but it will make a difference in sound.

[Bruster]

1, Use .080 main jets,
2, FRESH premium fuel mixed @
3, 40:1 premium synthetic oil,
4, timing set @ 21 degrees
5, and prop to spin 5800 to 6200 RPM.

Always worked for me:D

[Raceman]

Those are good rules Bruce (even though I like the extra insurance of 32:1 full synthetic in mine). I'd also add a #6 of always running a fresh waterpump as it seems especially critical on the inlines.

[crazy horse]

The water pump thing is a good rule . I always pull my case in the fall and store in in my shop so the water pump get done every year, I thought that the pump on a jacked up motor took a beatin any how and impellers are cheap. Hey Bruce, Did you get any of that damn clipper that blew thought here :(. We got 10 in. in 12 hours, Man do I love it here :p.