Johnson 8hp power question HELP!!!

[Sol Searching]

I've got a 2000 Johnson 6 horse (used 5 times) that I put a new 8 horse carb on (I was told that the only diff. between the 6 and the 8hp is the carb.) I mounted it on a 8.5' inflatable(110lbs.). With myself (220lbs)and my wife (115lbs) in the boat. The boat wouldn't even get up on a plane, it just plowed water. I even had my wife step out and I went on my own and the same thing happened. I sounds like it is reaching full throttle and I even took the helmet off and "floored" it manually and still BLAH! I would think that a boat that small with 8hp would fly, am I wrong or is there something I am missing? P.S., I never used the motor on the boat with the six hp carb.

 

[CATransplant]

Re: Johnson 8hp power question HELP!!!

There are several differences between the 6 and 8 in that year. Just swapping the carb won't do it.

That said, you're starting out with about 300 lb. at the back of that little inflatable. That's a big deal. I doubt it would plane for you with even a real 8hp. Inflatables aren't that easy to plane in the first place.

 

[Sol Searching]

Re: Johnson 8hp power question HELP!!!

Bummer, thanks for the info. I guess I need a bigger motor!

 

[Whoopbass]

Re: Johnson 8hp power question HELP!!!

I recently bought a 9' inflatable that had an older 10 hp Honda 4 stroke. With two people in it done about 15 mph and planed. The outboard had a hydrofoil on it so it planed quick.
I sold the Honda and put an older 15 hp Sea King on it. I was by myself and when I took of the boat would stand on end and take along time to plane because there was too much weight in the back of the boat. For safety reasons I only got the boat up to 15-20 mph but it would have went faster.
i then sold the 15 hp Sea King and put a newer 6 hp Suzuki 4 stroke on it. Took the boat to the ocean and got it up to around 10 mph but didn't want to go any faster because of the swell and chop. It got up and planed but I wasn't able to open it up for any length of time to see what it would actually do.
If my little 4-stroke can plane my boat I would imagine your 6-8 hp motor would do the same so your motor has issues and it probably has something to do with the new carburetor.
By the way I weigh about 180 lbs.

 

[CATransplant]

Re: Johnson 8hp power question HELP!!!

By the way, I went and looked at the parts blowups and lists for the 2000 6 and 8 hp Johnsons. Aside from the carburetor, the only difference is the engine block. That means the porting is different. The 8 hp carb won't do it.

 

[mikesea]

Re: Johnson 8hp power question HELP!!!

There are a lot of myths out there about 'Just put a bigger carb on"like the 9,9 and the 15 exhast is different too

 

[CATransplant]

Re: Johnson 8hp power question HELP!!!

There are a lot of myths out there about 'Just put a bigger carb on"like the 9,9 and the 15 exhast is different too

Depends on the year. For some of the earlier ones, the carb was the only difference. Trying to find a 15hp carb for those models, however, can be an exercise in futility. Everyone wants one, and there were lots more 9.9s sold than 15s.