Late Merc 3 cylinder 40 HP to 50 HP conversion?

[FlyBoyMark]

I have been through the entire parts list and numbers for both engines and they are identicle<br />except for the stickers. Same carbs, block, reeds, electonics, trigger, flywheel, linkages, jets,<br />pistons, crank, exhaust tubes, blah, blah.....<br />I was going to buy a 60 HP for my boat but they no make no mo'. <br />So I wanna juice up my 40 HP. Any Merc mechanics out there know what the difference is?<br />I suspect it's just a timing adjustment to advance another few degrees for that last ten ponies.<br />My motor is out of warranty, so it's ok to mess with it. Anybody know?

 

[skier]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

Sorry, but it's exhaust port size and port timing that makes the difference. It is easier and cheaper to buy a bigger motor. There is an option though. Find a 50 of the same year and have the powerhead swapped. I did it with a 115/140. It cost 800 vs 2900. Do that math.<br /><br />Craig

 

[FlyBoyMark]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

Nope buddy...the parts are all the same in these two motors verified by Merc. There are no part variations. Its got to be a different thing....I have tediously gone through the numbers twice. Port modifications would have a different part number like the 60 hp does with its block. The blocks on these engines are one piece except for the crank cap. And like I said, Merc 6O HP 2 cycle is no longer made...Mercury has discontinued production of all 2 cycle above 25 hp except for Optimax......fresh off the press. Need short shaft engine......

 

[skier]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

The size of the exhaust port and/or placement is not a part. You can't get any more air/fuel into the cylinder than the exhaust porting will allow out of the cylinder. That's how they got so many HP ratings from the inline 6 blocks (90-150) as well as all motors with the same cid and different HP.<br /><br />Craig

 

[FlyBoyMark]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

Merc ..I undertand that. The block is one peice milled assembly.....the part numbers are EXACTLEY the same, not diagram numbers, actual Mercury part numbers you use to order with, and so are the complete power head assemblies. If there is a difference in mill work they then would have different part numbers like the 60 hp does. You are correct in most circumstances about port timings and I'm thoroughly familiar with this...I do work on these engines to repair blocks but in this case they are IDENTICLE.......Guess I need to invest in two $35.00 dollar manuals.....

 

[FlyBoyMark]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

Ok Here's the scoop..the only difference between a late Merc 3 cyl. 40 HP and 50 HP is the jets. The 50 has SMALLER main jets only. Anybody wanna bite?

 

[trevorcday]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

What year (or S/N) is your motor? I checked for 2000 model 50 and 60 2-stroke and they have a different part number for the cylinder block and crank shaft.

 

[trevorcday]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

Please ignore my previous post I somehow thought you we were going from a 50 to a 60. The part number for the three carb's is different between the 40 and 50. I am sure you will find that the throat of the carb's on the 50 are a lot bigger. Also, the 40 has something called a reed stop that the 50 does not.<br /><br />Just today I did a conversion like this on a 2001 75elpto to convert it to a 90. It was an unqualified success. Running on a 16.5' aluminum boat we went from 5200 RPM with a 21" prop to 5600 RPM with a 23" prop! Top speed improved from 43 mph to 50 mph.<br /><br />Doing the carbs on your motor may be worthwhile but you will need to buy the right parts which won't be cheap. The three carb's for the 75/90 were $450 Canadian (approx. $285 US). You also need to check the timng spec's. The 90 had 2 deg. more advance than the 75.<br /><br />If you want to go ahead with this I can fix you up with the parts you will need. E-mail me at trevorcday@hotmail.com if I can help.

 

[FlyBoyMark]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

Mrmerc..All specificatoins for these motors is the same 40 to 50 hp per year produced. There are 6 different carbs for each motor and they are the same list to list. All of the carbs are the same except for main jets. One is no bigger than the other. If that were the case then the blocks would be different with different numbers for the porting mill work. They are both rated @ 5000 rpm. If you understand what peak E.G.T. is, you will understand why this is the only difference. The 40 Hp runs before peak EGT the 50 hp runs @ peak EGT NOT beyond....another words the 40 runs slightly rich and produces only 40 hp. But not enough to sputter. The 50 is tuned to run at best power or peak EGT. The 40 would actually burn a small amount of fuel more than the 50. The 50 is not running "lean" but jus' rite. The jet size variation should be no more than .004" smaller. Reeds and all associated intake hardware is the same on all of these motors from about 2000 forward. If there are any variations than it will be same for both motors produced at the same time. And as all of you know mixture in a 2 cycle makes the difference considerably on how the motor runs. What happens when you go up in altitude 5,000 feet? You rejet for better power! And by the way guys, don't try this because it will void your warranty or fry your engine if ya try it on some other outboard. Mercury was slick on this one.....<br />E.G.T.-exhaust gas temperature

 

[trevorcday]

Re: Late Merc 3 cylinder 40 HP to 50 HP conversion?

FlyBoy:<br /><br />Your 40 has the following Carb's 823799T7 top, 823799T8 middle, 823799T9 bottom. A 50 has different carb's 824902T16 top, 824902T17 middle, 824902T18 bottom. Also in the reed assembly your 40 has a reed stop p/n 825267 which is replaced by a retainer p/n 812879-1. Trust me the carbs are different. The carb's will have a bigger venturi so they can flow more air and make more power.