1983 Mercury 25 Hp conversion

[2dbit]

Well, I tried doing this all on my own. I did lots of research and from what I can tell, this might work.

I have a 1983 Mercury 18Hp which I plan on converting to a 25Hp. I reviewed every parts list for the two models of the same year and it seems that the only difference is the carburetor throat and jet size.

Is there anything else I should be looking for? The pistons, rods, powerhead, reed block/stops, and ignition components all match.

The carburetor in question is a Tillotson model BC1C. Looks as if this specific carb was used on 25Hp Mercs from 1980-1983. It doesn't look as though I can convert to a newer style carb, the plate which the carb is mounted to is a different p/n.

Anyone have any experience with this? Any tips or pointers that I can use in my search for this carb, or the upgrade in general? Is this even worth it?

 

[sacalait59]

Re: 1983 Mercury 25 Hp conversion

Don't have any advice but would like to hear how it turns out.

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

Well, at this point I'd be happy to locate a used 1980-1983 25hp carb. I have a feeling that most people who trash their old mercs don't part them out, probably just recycle them. EDIT

 

[achris]

Re: 1983 Mercury 25 Hp conversion

Over the last few years we (all the major contributors to this forum) have been though this issue some many times we have lost count.

You may well succeed in your attempt to recreate Dr Frankenstein's monster. But before you go any further, consider the next person who has to try and fix that engine, without you standing at his side telling him which parts you changed to produce this bastard child.

From experience, there is nothing more frustrating than trying to work out what some half-arsed, backyard butcher has done to an engine before you can even start to think about how to go about fixing it without having to resort to binning all the non standard parts (and the cost of putting standard one back on) because it doesn't run properly.

God created it as an 18hp engine. LEAVE IT THAT WAY!!! If you want a 25hp engine, sell the 18 and buy a 25.....

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

While I absolutely respect your opinion achris, I have to disagree. This engine was created as an 18hp model and was purchased by a single owner as such. This motor has been in possession of that original owner since 1983, and will continue to be until the day the pistons ring like bells. (or meets its ultimate demise with a rock).

I recognize your point when it comes to Frankenstein-type motors where parts that do not belong on that motor have been rigged in such a way that they will operate. This is not the case as a side-by-side comparison of both of these motors will yield ALL identical components aside from that carburetor, a carburetor which the only three items that set it apart from the 18hp model are the carburetor throat diameter, throttle plate, throttle shaft, and jet. (all seals, and attached components match, meaning when the carb is rebuilt the rebuild kit for an 18 and 25 are the same p/n.)

In fact, it goes beyond that. Per the Mercury manual, the tuning procedure for the 18 and the 25 models match. What it all boils down to if this motor were ever sold, and the original carb was not placed back on, the new owner would wonder how an 18hp motor had so much power.

The physical change to this motor will be so slight, yet the power yielded will be a 38% increase.

 

[grandpaclint]

Re: 1983 Mercury 25 Hp conversion

lololololol---------i wouldn't touch this with a 10 foot pole

G.O.F

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

ok, you got me...G.O.F.?

 

[achris]

Re: 1983 Mercury 25 Hp conversion

ok, you got me...G.O.F.?

http://forums.iboats.com/showthread.php?t=413617

scroll down to reply #20, and start reading from there....

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

ha ha ha....that is terrific I do have to agree with G.O.F.'s original rant about cost of sale vs. cost of production. Just replaced the prop shaft on this motor after a severe rock strike. You can't help but stare at the new prop shaft, a less than 1lb piece of machined steel and think....$300....

 

[Nickledimed]

Re: 1983 Mercury 25 Hp conversion

If you do not ever plan on selling the motor, Im right behind you.
Go for it.
But with all due respect, I am currently operating on 2 frankenmercs and I have to say this, if I knew who franked these 2 motors I'd club them.
Frankenmerc is a good option from anouther offensive word I would use here...lol
Anyways, go for it, post your results, take alot of pics and keep us posted.

Scratchs head, I wonder what it would take to change my 83 115 merc to a 150?...lol JK

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

Ha ha, take lots of pictures They would be the most confusing and boring pictures ever! (I really meant it when I said the carbs are identical) Can you tell the difference?
http://www.crowleymarine.com/mercury-outboard/parts/677_7.cfm
http://www.crowleymarine.com/mercury-outboard/parts/676_7.cfm

Anyways, if this motor were to ever go up for sale (and I meant it when I said it was sticking around till it just won't run anymore) I'd slap that 18hp carb right back on it so that it's sold as it is meant to be, and sell that 25hp carb separately.

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

(I'm sure that plate (#40) catches the eye first. That plate is for motors sold in Italy)

 

[cannonford57]

Re: 1983 Mercury 25 Hp conversion

not trying to pile on here but what are ya trying to do here....buy skis,probably not,maybe a neck brace for the jump in acceleration,nah....bet not again,i got it,the blurring increase in speed you'll get on top end....just kidding with ya but the truth is if you find and buy a carb,you have almost doubled the value of your engine and i'm afraid be very disapointed with your outcome...if its a project you lie awake at night and think about,by all means go for it.....good luck with it

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

Hey, whatever helps haul 4 overweight guys in a little metal boat into the wind...ya know?

 

[cannonford57]

Re: 1983 Mercury 25 Hp conversion

gotcha my friend,if your that dedicated to it i wish ya nuttin but the best,ever think bout fishing downwind for a change?

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

downwind? The fish would be expecting that. . . . . Besides, the farther downwind you go, the farther upwind you'll have to come...eventually.

 

[grandpaclint]

Re: 1983 Mercury 25 Hp conversion

Well, at this point I'd be happy to locate a used 1980-1983 25hp carb. I have a feeling that most people who trash their old mercs don't part them out, probably just recycle them. EDIT

ok i said i wouldn't touch this, however,what with outboards listed 9.9 hp
same as a 15,hp,,,the only difference being the carb, and your'e 18, converted to a 25.with just a carb change,following that logic,
if you could put a holly double pumper on the same motor you could possibly
approach 100 hp.

heh heh heh heh

G.O.F SAID THAT

 

[grandpaclint]

Re: 1983 Mercury 25 Hp conversion

ha ha ha....that is terrific I do have to agree with G.O.F.'s original rant about cost of sale vs. cost of production. Just replaced the prop shaft on this motor after a severe rock strike. You can't help but stare at the new prop shaft, a less than 1lb piece of machined steel and think....$300....

AMEN TO THAT and new bc1a carbs are available for $88.88 in puerto rico
but they wont ship to USA.
one wonders why they are not available here,,,,oops they may be
for $279.00 + mondo shipping

oh by the way i ordered a so-called rebuild kit for my bc1b carb,,what a joke
REBUILD MY BUTT.
$8.50 SHIPPING FOR A 3 OUNCE ENVELOPE
in the boating business you get ripped a new one,no matter which way you go.

 

[2dbit]

Re: 1983 Mercury 25 Hp conversion

Yeah the 3 ounce envelope that the envelope itself probably weighed 2 right?

Speaking of outrageous shipping fees.... During my quest to obtain a new propshaft for the 18, I first went to order from a place that offered excellent pricing. Not until checkout do you see that they wanted to charge $110 shipping for a less than 1lb part. (seriously. no joke)(the second place taught me that even though it shows "in stock" it's not...nor will it ever be...of course they processed the order and allowed me to wait a whole week before I called and asked about it....they didn't even know I placed the order) What I've learned? CALL FIRST.

 

[grandpaclint]

Re: 1983 Mercury 25 Hp conversion

Yeah the 3 ounce envelope that the envelope itself probably weighed 2 right?

Speaking of outrageous shipping fees.... During my quest to obtain a new propshaft for the 18, I first went to order from a place that offered excellent pricing. Not until checkout do you see that they wanted to charge $110 shipping for a less than 1lb part. (seriously. no joke)(the second place taught me that even though it shows "in stock" it's not...nor will it ever be...of course they processed the order and allowed me to wait a whole week before I called and asked about it....they didn't even know I placed the order) What I've learned? CALL FIRST.

good ol AMERICAN GREED,and for what? keeping a product on their shelves
gathering dust, and paying an inventory tax every year.

if you ask them it will be shipping and handling,,,,that means if i go to
NAPA auto parts, and a guy looks up my part, goes into the warehouse
and gets my part, i owe him for handling,,,,,,,,,I THINK NOT.

just a bunch of greedy business men,or assh$$$$ as it fits

G.O.F said that