upgrade 25 Evinrude to 30

I have a 1998 Evinrude 25 that I want to convert to a 30. I have many friends that have succesfully converted thier 20 or 25 to a 30 by changing the carb. This has been done to models older than a 1990 model. I had a 35 carb and intake that I bolted right on to my 1998 Evinrude 25, but I didn't get any more horsepower. Obviously there is something else that needs to be done to increase horsepower other than just changing the carb for newer model 25's. Does anyone know what else needs to be modified to successfully convert my 25 to a 30?

Re: upgrade 25 Evinrude to 30

Defreeman; I have a 1990 25 hp Johnson that the previous owner had converted to a 30 hp by a very reputable marina here in northern Illinois. I have a 16’ Lund Explorer and am very happy with this boat/motor combination. According to Joe Reeves the 25 and 30 have the same block, cyl head, crankshaft, rods, pistons, leaf plate, leaf valves etc. The differences between the two are as follows:<br /><br />The throat hole venturi on the on the carb and manifold is larger on the 30 than the 25.<br /><br />30hp is hit at 5500 rpm. 25hp is hit at 5000 rpm.<br /><br />The cam, which is attached to the magneto armature plate, is different. The 30hp cam is # 326876. The 25hp cam is # 334750.<br /><br />The orifice at the extreme top of the carburetor is different. The 30hp is # 39 (.039) # 334568. The 25hp is # 30 (.030) # 317473.<br /><br />The high speed jet, located at the center bottom portion of the float chamber is different. The 30hp is #65D (.065) #327541. The 25hp is #51 (.051) #331567.<br /><br />I hope this information is helpful to you. It is my understanding that trying to increase hp is usually not a good idea, however I think in the case of this particular motor it works well.<br /> <br />I’m not 100% sure, but I think the latter model 30hp has different exhaust port timing.<br /><br />I think I would check with Bombardier Customer Support at 847-689-7090.

Re: upgrade 25 Evinrude to 30

I'm far (far!) from an expert on this, but I have the same situation with my '77 9.9. Up to 1981 all you had to do was change the carb. After 81, a 'tuned' exhaust was used with the larger carb, and apparently the 9.9's exhaust was smaller than previously. <br /><br />Perhaps yours is the same?

Re: upgrade 25 Evinrude to 30

From what I understand, an Evinrude 20, 25, and 30 have the same powerhead and the respective horsepower is attained by getting more air and fuel via a larger carb. I've seen horsepower increased by changing out the carb many times on older model 20's and 25's. But, the question still remains: what has to be altered in addition to the carb and intake on a 98 model 25 to make it a 30? Are the powerheads the same? If so, why can't you achieve the extra horsepower by air and fuel by changing the carb? Any help would be appreciated. Thanks Jonnielund for your insight. I had a friend that had a 90 model Evinrude and made it a 30 by simply changing the carb. Ran like a top.

Re: upgrade 25 Evinrude to 30

Best thing would be to get a 98 J/E factory parts catalog that covers the 20 to 30 hp and compare part numbers. I have a 95 catalog and it looks like the carb is the only difference.The weird thing is, my 30 has what looks to be the 25 carb..but it's a millitary motor with a number that says it's a 35hp and 5 years newer than what it looks like (parts wise). There might be a different power pack and timing measures to get your motor up to 30 also.

Re: upgrade 25 Evinrude to 30

The answer is in the info Johnnielund got from Joe. Its in the rpm. You still have the same bore, stroke and gear ratio. You can put the 35 carb and other parts on but if you still turn it the same rpm, youll still be only using part of the available power.<br /><br />The other thing is that your hull has to respond very well to small torque increases. We run into this all the time. Thats why we work so hard on maxing out the set up BEFORE we make any motor mods. Without doing that you get the same result as you did most times.

Re: upgrade 25 Evinrude to 30

Isn't compression ever an issue? I would think that a change in HP would be accompanied by an increase in compression.<br /><br />Just askin'<br /><br />Mark.

Re: upgrade 25 Evinrude to 30

Not necessairly. You still have the same bore and stroke (volume) pumping at the same rate (cranking speed) into the same area (combustion chamber).<br /><br />Now, while there may be some small differences in heads dfreeman didnt say he changed that. But even if he did, if the wot rpm's are still below max you get the same result. It doesnt matter if its a 2 cylinder or a V8.

Re: upgrade 25 Evinrude to 30

I remember when we (kids) wanted a few more hp out of the old Yamaha enduro bikes we would just glue some emery paper to a piece of plate steel and rub the head on it to raise compression. Poor mans milling machine. Worked well, but metal head gaskets were needed and sometimes the rods would let go do to over speeding/over stressing the engine. Man, those babies would rev after that mod!

Re: upgrade 25 Evinrude to 30

Take that same dirt bike before the heads are done and hook a trailer with a large load to it so it cannot get max rpms in high gear. Itll struggle at best. Now mill the head but leave the same load on it so you still cant get the proper rpms. <br /><br />You could possibly accelerate a bit faster but not much is going to happen until you lose the load.

Re: upgrade 25 Evinrude to 30

This has previously been discussed a lot, do a search for 25 / 35 HP difference. As there is a limiter in the 20 HP carb, changing this carb to 25 or 35 type will mean a lot, the 20 cant reach max HP RPM's because of the nylon reducer in carb throat. Trying to increase from 25 to 30 will hardly be noticeable, unless boat is VERY light.

Re: upgrade 25 Evinrude to 30

My boat is very light, 185 pounds dry weight. I have a 1954 Alumicraft FD semi-V. I use it for running the river and duck hunting. There is a pretty signifigant difference in a 25 and 30 on this boat. Is there anything I can do to make my 25 a 30 besides changing the carb? I have a friend that had a 1986 Johnson 20 and he changed out the carb for a 30. It made a huge difference in power. In his words its the smoothest running motor he has ever owned. This coming from a 73 year old Louisiana duck hunter who has spent most of his life on the Ouachita River.

Re: upgrade 25 Evinrude to 30

Here is what shows as different in my 1996 parts catalog,<br />#1-throttle control cam and screw<br />#2- carburetor<br />#3- Intake manifold<br />#4- Bypass cover assembly<br />#5- hose from intake to bypass cover<br /><br />everything else has identical part numbers for 20,25 and 30 hp motors.

Re: upgrade 25 Evinrude to 30

bump

Re: upgrade 25 Evinrude to 30

I don't understand the bump. I think that Harker did a pretty good job of telling you what the part differences are. All the other posts explained things and their opinions very well. I'm not trying to dis anyone hear but is there something else you are looking for?

Re: upgrade 25 Evinrude to 30

I forgot to mention the "magic" screw that is located inside the power pack...heh heh heh...I hear stories from guys, that know guys, that heard it from some guy..about just turning some screw is the difference between 20 and 30 hp..or 9.9-15hp...I guess there are quite a few screws that you need to turn(to change the parts).