Carb swap

[Skidz]

Hi everyone, I have a 2000 Johnson 25, #J25TESSD that I would like to get a little more out of if possible. I was hoping that a carb swap with a 30 might do the trick. I have looked various part numbers up, and it looks like a #0439377 carb would work no problem. The intake manifold is the same P/N, as is the primer assy.

What say you? Would I get a few more horses out of this? Or am I barking up the wrong tree?

Thanks,
Skidz

 

[Daviet]

Re: Carb swap

I don't think you are going to gain anything. Is your engine turning the proper RPM at WOT? A 2-cycle makes horse power by turning the correct RPM.

 

[Skidz]

Re: Carb swap

I'm turning right at 4980-5000 at WOT with a 11 pitch prop. Cav plate is about 1/2" above bottom of boat. I know I'm underpowered. This motor on a 16/48 mod v aluminum boat that's pretty heavy. I went down to the 11 prop hoping to see a bigger difference, but it wasn't what I'd liked. On my old boat, which was smaller and lighter, the factory 13 pitch prop would turn about 5350-5400, and it went plenty fast. Now, the new boat is more of a dog. I am looking to get a 30-40 hp engine, but the budget is tight.

 

[Daviet]

Re: Carb swap

Sounds like the RPM is close, maybe thats all you're gonna get.

 

[watergecko]

Re: Carb swap

Remember its not just an "engine", its a balanced group of parts working in harmony. Ur lower end is different than that of a 30+ hp. The 20/25 are one and the 30/35 are another. If u boost the power you will overtax your gears. Youll have to tweak other things to gain speed, cutting weight, waxing hull, etc.

 

['94 Pro-Line 170]

Re: Carb swap

Ur lower end is different than that of a 30+ hp. The 20/25 are one and the 30/35 are another. .

Not true, I checked the BRP parts catalogs. The short gearcase for the 25 and 30 are the same (0434763). I have a 2003 on a 16ft mod V, and I'm thinking of doing the same thing. Should burn more gas but get the same rpms with a bigger prop which equals more speed. Still will burn less and weigh less than a 40hp. There's no difference in the stock 25 and 30 except the carb and the stickers. If it's not a 5hp improvement, then it's false advertising/fraud. This is simpler than say the old 115/140 4-cyl crossflows which also had different manifolds along with different carbs.

 

[bob johnson]

Re: Carb swap

as for the 25 and 30 hp interchange... I can say from having 90 and 115 hp V4s f the same model and years that there is a lot more different than they say...

if you check interchangability they will say the 90 hp head will fit on the 115 block and vise versa....but they are DIFFERENT heads....one haveing a chamber .080" DEEPER

also i looked into both blocks and the ports in the sleaves are way different...!!!

plus the carbs are different..

the book says the carb interchange....and they DO... they BOLT UP>>>>does that mean they interchange?? not hardly



this misconseption goes DEEP into the industry...
COMPANYs who sell remanufactured blocks will tell you the same V4 60 degree looper block is used on a 90 hp or a 115 hp...the different is the carbs and heads...but it isnt true!!

the ports in the sleeves tell you what HP the block is made for!!!

but people believe what they want...and if they thing their motor is going faster, then they are happy!


the block for the 2003 25 and 30 hp units have DIFFERENT part numbers!!!...means something is different!!!


bob

 

[Whoopbass]

Re: Carb swap

You might gain a 2-3 mph top end max. Most people that do a carb swap see power gains.
This topic has been discussed on here in the past so do a search and read up. Most topics are on older 80's motors from 20-35hp motors.

 

[Skidz]

Re: Carb swap

I went ahead and did the modification, and I was very pleased. I gained about 5 mph, and now I am just a hair away from 5500 rpm's, using a 12 pitch prop. Works great for me.