40hp hop ups? any ideas?

I just picked up a 1979 40hp merc 2 cylinder, single carb. Its on a little sort of race runabout. I have a 18inch stainless chopper from a C class tunnel and the prob is great. But I would like to get soem more power out of the motor, baicaly tune it and do some mild porting. Nothing that would harm it though of course or to much $. I can't buy a 50hp because I want to keep the weight down. Was thinking of porting out the carb like the link below<br /><br /> http://www.super-chip.com/mercury-outboards.htm <br /><br />anyone have any other ideas? Did they ever make a quicksilver lower unit for these motors? Whats the diff between the 44sx and this, will that lower unit work on mine?<br /><br />Thanks<br />mike

Re: 40hp hop ups? any ideas?

The unit you are loking for is off a 35SS built in about 1980 to replace the 55H but did't pan out they are still used in someplaces for Hydro

Re: 40hp hop ups? any ideas?

The 35SS is a very rare bird. If you do find one, be prepared to pay a pretty penny. A 40hp will not simply bolt up to the Mark 55H or 44XS lower unit, either.<br /><br />If you're running a stock 40 now and have a tricked out prop, simply find a similar vintage 50hp - same lower unit and your prop will work, plus you get a 25% increase in power... Far more than you'll get by any mods to the 40, and it'll be much more reliable...<br /><br />- Scott

Re: 40hp hop ups? any ideas?

I'll have to keep my eye out for the 35ss nevery heard of it. As for the 50hp, how would a change in lower unit increase power? Or do you mean a 3 cylinder 50 just get one of them? I can't get anything that weights more, thats why I picked this motor because its very light for 40hp only 20-30lbs more then a 25hp with electric start. I think I might rear pitch the prop to a 19 and try that, and see if I can find another stock carb and bore that out so if I screw it up I can put the stock one back on. Any other ideas?

Re: 40hp hop ups? any ideas?

Those 402 engines were hard pressed to stay together stock and I don't think there is much there to tinker with maybe the reed blocks and the ports

Re: 40hp hop ups? any ideas?

Adding MORE pitch will not help your situation as you want to keep the RPM high enough to make the horsepower. If you lug it down with more pitch you're likely going to cook it. The 40hp swinging an 18-inch prop is a lot as it is. Have you had a tach on it?<br /><br />The 4-cylinder 50hp Merc isn't much heavier than the big-bore 40hp twin. They use the same lower unit so your prop will fit it (didn't mean to try the 50 lower on the 40 upper). I am not familiar with the 3-cylinder 50s so I can't say in that regard. The 4-cylinder 50s actually like to be spun up a bit and can handle some extra revs without eating a rod.<br /><br />As Laddies pointed out, the 40s didn't have a great track record in stock form. Good enough motors, but really can't take a huge beating. They liked to break crankshafts when spun out beyond their operating range.<br /><br />Best bet is to make sure you're revving at the top end of the rev range and that the motor is as healthy as possible.<br /><br />- Scott

Re: 40hp hop ups? any ideas?

I know the 4 cylinder your talking about, the classic 50 I think they called it, ya its a pig for weight over 200lbs, my boat will sink if I put that on. I had a 25merc on it with the same prob 18 pitch and I think its a 13 dia. It ran good crap out of the hole, rpm where low enough top end so I raised it up and agained about 5mph running 43mph on the gauge at 5600-5800 WOT. I did some caluclation and with the same prop slip it should run 46-47mph but I don't want it reving that high I want it 5600 max so I'm hoping to keep the prop in the water and keep the rpm at normal level. I know the 2 cylinders are not the greatest motor but they are light which is what I need. IF was going to go with a higher hp motor I would get a non merc. I"m hoping to tune this motor and keep the rpms stock but still have a good topend. Topend is all I care about really so if its running alittle high in rpm then I'll see about repitching the prop. And if I repitch it then I would like to do some minor mods to it like mild porting.