1990 Evinrude 20 HP convert to 25 HP (Model # E20CRESB)

[the-outdoorsman]

I found one thread on here about this and it was for an older motor. It looks like I just need to bore out the intake to match the carb. I went to BRP to compare carbs. All the listed part numbers seem to be the same for the carb but if you purchase a carb assembly the part numbers are different. I was wondering if anyone has done this to a 1990. Thanks for any help you may have.

 

[jimmbo]

Did you compare Part #s for induction system, for the block, exhaust components as well?

 

[matt167]

20-25hp on a 1990 will involve a new carb and intake. The exhaust is the same. the restriction is done with the carb and intake. 20hp's older than 1988 also use the 25hp carb. If willing to pull powerhead and swap exhaust and a couple other things, 30-35hp can be achieved using 30-35hp intake and carb, exhaust as well as timing is different as I recall.

keep in mind that the 20hp bracket is pretty light duty

 

[flyingscott]

The 20-35 hp 32 cid blocks from 1985 on with the through hub lower unit are all the same. Putting a 25 hp carb on your will make little if any difference usually not enough for the hassle. There is absolutely no difference in the brackets between those motors. I would not trust Evinrudes parts fiche when it comes to the carbs either. Evinrude has a tendency to list one carb for different motors and they are not the same.

 

[jimmbo]

Keep in mind blocks can be the same, but changes in port timing can be attained by making changes, even slight ones, to the pistons.

Flyingscott is correct about service parts lists often listing a common part, even though the factory parts were different. My guess is to reduce inventories as they really don’t make much difference.

Making almost twice the Horsepower(20 to 35) from the same displacement and only an extra thousand rpm, and no other changes except a carb, is really stretching credibility.

Because of tolerances allowing Deviation(+/- 15%) from rated HP, the 20 could be a 23 hp, while the 35 could be a 29.75, less than a 7 HP difference, and one sounding more realistic and attainable.

 

[racerone]

They even used that same block for the 15 HP " ZEPHYR " sail drive.--------Very small intake ports in the block.

 

[jimmbo]

They even used that same block for the 15 HP " ZEPHYR " sail drive.--------Very small intake ports in the block.

Makes for a motor with lots of low end torque, does make it Asthmatic at higher speeds

 

[flyingscott]

The 20-35 hp blocks all have the same porting except for the Zephyr. They start with a 35 hp block and choke the hell out of it to get it to 20 hp. But porting and internals are all the same.

 

[F_R]

Better buy a nice GPS to go with that carb. You'll need it to detect any difference between 20 & 25hp.

 

[the-outdoorsman]

Sounds like I better pass on this project. I had found another thread about this a couple of years ago but I can not find it now. The guy claimed when he did his he really didn't notice much gain in speed but the motor idled a ton smoother. I would have been happy with that as my motor does not idle well and eventually dies. I use this motor for duck hunting in late November and December and it is usually pretty cold. Below freezing most days and sometime in the single digits. Maybe it will never idle well in that cold. My 20 horse merc always did. I rebuilt the carb and put a new fuel pump on it and also a new fuel line from the motor to the gas tank and it had no effect on it.

 

[flyingscott]

Actually the 20 will idle better than the 25 hp. Check your thermostat and play with the low speed mix see if that improves it.

 

[the-outdoorsman]

I replace the thermostat already. When I adjusted the low-speed mix, I turned it in until it started running rough and then I turned it out until it started running rough and then turned it back to the middle of the two. Still doesn't idle proper. It idles for a bit but then it acts like it is loading up and dies.

 

[racerone]

Why set it in the middle ?----Why not adjust for smoothest running and no stalling on acceleration.

 

[the-outdoorsman]

Why set it in the middle ?----Why not adjust for smoothest running and no stalling on acceleration.

I did that when I rebuilt the carb and never found a place that it wouldn't stall out. That is when I set it in the middle. It is worse in the cold weather but it still will stall in warm weather also. Just takes a little longer. I am just a garage mechanic but I usually can get something running right.

 

[oldboat1]

Ignition overheating can be an issue with the under-the-flywheel power pack, although I'll guess that would show up with high speed running rather than idling after a cold start. But check for strong spark when it’s acting up — approx. 1/2 inch sharp spark using an adjustable open air tester. What are the compression numbers?

So…If it can’t be dialed in, reed valves could also be the problem. And there may be an exhaust blockage somewhere (weeds and reeds or mud partially blocking the thru-hub exhaust, or nests up in the leg after storage). A clean 50:1 mix is essential. Water doesn’t burn well. Solvents used in the tank can clog small jets in the carb, likewise requiring disassembly and thorough carb cleaning.

 

[the-outdoorsman]

Ignition overheating can be an issue with the under-the-flywheel power pack, although I'll guess that would show up with high speed running rather than idling after a cold start. But check for strong spark when it’s acting up — approx. 1/2 inch sharp spark using an adjustable open air tester. What are the compression numbers?

So…If it can’t be dialed in, reed valves could also be the problem. And there may be an exhaust blockage somewhere (weeds and reeds or mud partially blocking the thru-hub exhaust, or nests up in the leg after storage). A clean 50:1 mix is essential. Water doesn’t burn well. Solvents used in the tank can clog small jets in the carb, likewise requiring disassembly and thorough carb cleaning.

I jumped into this project headfirst without checking the depth of the water.lol. I have the intake off already so now I need to get the new gaskets for the intake and carb before I can test the spark. I checked the compression a couple of years ago and it was good in both cylinders but I can't remember what it was. I just remember it was good when i inquired about it. I think it was around 100 in both cylinders but not positive. I will check that again as well. I bought a new gas tank so that should be fine. The exhaust blockage has me wondering. I have gotten the motor in mud more then one time. It has also been run in the lake so would that clean it out? If not, what would be the best way to make sure it is clean and no blockage? A buddy of mine said a friend of his has a late 80's 20 hp like mine and he bought a carb and intake for a 30hp and put it on his 20hp and noticed a decent increase in speed. He said he didn't do anything else to the motor. He said he found the parts on eBay. I was searching for just the intake and couldn't find that. I would probably invest a couple hundred if that would work.

 

[flyingscott]

It will work the timing is the same and you need the intake and carb. You might want to address your compression issues before you spend any money on a carb. 100 psi is not great and is pretty borderline for that motor. So recheck that and make sure your cam roller is in good shape and your link and sync is correct. My 20 hp that I dropped a 30 hp powerhead into was no faster than my 25 hp Merc. It was also terrible on gas so maybe you should get your motor running right before you spend a bunch of money.

 

[the-outdoorsman]

I agree with what you are saying. I may just leave it at a 20 hp and get it running good. I probably only run this motor 10 times a year and usually just across the lake and back. I will post back on my compression when I am able to check it. I am going to have to order the gaskets. I don't have anywhere to buy them close to me. Thanks, everyone for taking the time to post up ideas and suggestions.

 

[jimmbo]

A lot of work/hassle to maybe gain 1 - 3 mph
We had a 79 25, and an 80 35, on the same hull. there was only 2 - 3 mph difference, the 25 did idle down a bit better and was less jumpy at off idle. Granted those years they had different midsections and gearcases.

 

[the-outdoorsman]

I finally got the motor put back together. I checked the compression and on the top cylinder it was 100 and the bottom one was 110. I had to buy a new cam follower because I broke it where it hooks up to the carb. Looking in my book it looks like thier is some adjustments that may need to be done. I know nothing about this stuff and my shop manual doesn't make sense to me. The roller lines up between the notches when the throttle is all the way turned down. Also, it tells me how to set the linkage to the correct place but that makes no sense to me either. Maybe someone could help me out in layman's term.