more hp out of my 20 merc

[atk81]

i have a 20 hp merc year 2000.
i've already swapped my 20 carb for a 25, tampered with the exhaust and the reed block. ny friend has a 25 merc and he can still get by my. is there any other differences in the 20 and 25 powerheads?

[will350]

I really don't know for sure but OMCs MO on differences between "same" displacement motors was mainly carburation,timing and (sometimes) internal exhaust tuning. You might check the part number on the CDI and see if it's the same. If it's not,the difference may lie in the advance curve and amount of advance (possibly the rev limiter too). You might want to take a peek at your friends prop too(assuming your boats are the same weight and style)
This is just a guess.
Will

i have a 20 hp merc year 2000.
i've already swapped my 20 carb for a 25, tampered with the exhaust and the reed block. ny friend has a 25 merc and he can still get by my. is there any other differences in the 20 and 25 powerheads?

[atk81]

juat looking for a few more threads on this topic
thanx

[DonChichoJr.]

Merc 20 & 25 H.p. ( '83 To Present), Are The Same Block.
In My Case. I Own A Mercosil Block, 25 H.p., Sea-pro Model. That I Bored To .040 . I Still Waitng From Wiseco For The Pistons. They Are Telling Me,they Will Be Available Probably At The End Of Abril.
I Lapped The Reed Cage And Installed A Boyesen Reeds, Polished All The Exhaust Ports And Close The Exhaust Releive Holes At The Cyls.
I'm Using A Cabela's Ss Prop .

I Think The Diffeence Between The 20-25 H.p. Are The Carb Jets (??)

Don

[Dago Fast]

What do you mean by lapped reed cages?

D. F.

[atk81]

exhaust relieve hole... now theres something i haven't done. where would they be situated??
atk

[John (Taylor) Gabrowski]

If it is the Merc 20-25 Loop recreational fishing engine, get some expansion chamber formulas and build and set on a set of pipes. I haven't heard anyone doing that anywhere yet but there may have been a first time. They say that one thing you can do to any 2 stroke to really wake it up is the exhausts, so that is the direction you can look. If its a crossflow/deflector Merc forget trying expansion chambers and look at a megaphone based exhaust system, few people are very satisfied with using looper formulas on deflector engines.

[Mark75H]

The exhaust relief hole is a tiny hole above the main exhaust port that makes the motor easier to start. At speed it has no effect and is a waste of time to modify.

You will get more benefit from addtional test time and fooling with props and motor height and angle. Spend money on a tach and learn what speed your motor develops best power.

[atk81]

thanx mark,
i like getting threads from guys like you who have the knowledge to let you know how it is. i really think i have my motor peaked to its best. and the only thing left is to adjust motor heighth , prop etc. its hard to get custom props around this area, and if i got to get them over the "net" IT JUST SEEMS TO BE TO BIG OF AN EXPENCE , because i really dont know what the motor needs for a prop and i may have to buy several to get the right one. i'd like to have 4 or five props to test with but thats not going to happen. my prop supply is sort of luimited to what mercury has to offer.
atk81

[atk81]

oh just another question... last year i was told to cut some of my exhaust pipe off. but i didnt like to because i was scared of loosing compression. do you thik this will help? if so , how much should i cut off?
one thing i did do was drill some small holes in the exhaust chambe close to the heel of the motor, to let the exhaust out quicker. this seemed to help a bit. but now i'm thinking on drilling more holes up higher on the tower. because the other ones are still under water. think this will help? or should i be carefull on how much exhaust i let out???
atk