Differnce between Johnson 40 & 55 HP

[Mob1]

Hi!
Just bought a old MOB-boat (man overboard/rescue boat). Even its more than 10 yars old, it have hardly been used. It's powered by a 1998 Johnson commercial 40 Hp. I've been trying to find the difference between the 40 & 55hp version of this engine. I've gone throug the online partslists I can find online. I find that there is different nozzles availeble, as well as two different numbers on the complete carb. However, when I run a search on theese different partnumbers, I find that all is used for many differnt engines including both 40 and 55 hp.
Anybody know something aboat this issue?
Looking forward to the Norwegian summer

 

[freddyray21]

Re: Differnce between Johnson 40 & 55 HP

don't think it is as simple as changing the carb, but others will chime in. There are a lot of threads like this. I would just buy a bigger motor if that is what you want.

 

[Silvertip]

Re: Differnce between Johnson 40 & 55 HP

Every engine manufacturer makes at least two, sometimes three, and even four different horsepower versions on the same displacement engine block. Carburetion, porting, exhaust tuning and ignition timing are generally the factors that change. On four stroke engines it is cam, compression ratio, carburation and exhaust. It is very easy for the manufacturer to create these variations but it is generally cost prohibitive for the user to make these changes, especially if porting is involved.

 

[F_R]

Re: Differnce between Johnson 40 & 55 HP

Use the correct parts and don't be trying to re-engineer the thing. Results can be disappointing and even costly. Very costly. Improper jetting can destroy it.

 

[Mob1]

Re: Differnce between Johnson 40 & 55 HP

I'm awere of the facts listed in the anwers of my qestion.. I just thougt there should be possible to find the difference looking at the partlists. However, when there is the very same partlist for a number of different motors, how do you know which part goes for which engine? As I told you earlyer, if I go throug the lists(same list refers to a number of engines both 40 and 55hp), it is all the same, but some items are listed twice.. Like if there are items from 1 to 34 for the carb. It is listed two of number 9 with different partnumber. How do you know which part to order?? There must be a way of knowing!!!