Installing a larger carb on my 55 SeaKing 12

[ohm116]

I have my 12 HP SeaKing and was wondering if it would be possible to swap a larger throated carb from an Evinrude or Johnson, say a 15 or 18hp, to give more performance?

 

[F_R]

Re: Installing a larger carb on my 55 SeaKing 12

I have my 12 HP SeaKing and was wondering if it would be possible to swap a larger throated carb from an Evinrude or Johnson, say a 15 or 18hp, to give more performance?

I won't be so bold as to say it won't work, so go ahead and try it if you want to. Matter of fact, I am doing the same thing right now, but on a different series.

I can tell you that you will most likely have problems with it, especially in mid range. It will probably backfire, miss, cut out, snort and whatever, due to being too lean. Reason: Carburetors are sized to work on a certain air flow velocity, which is determined by the cubic inches displacement of the engine. Pure and simple, the 12 has fewer cubic inches than a 15 or 18. Draw fewer cubic inches through the carb, and the air velocity is lower and it pukes.

But that doesn't keep us from trying.

 

[steelespike]

Re: Installing a larger carb on my 55 SeaKing 12

The 12 is 17.89 cubes the 15 is 19.94,the 18 22.
I think there are 3 different types of cam followers.Pretty sure the carb kit is the same for all earlier versions of each model.Carb with an adjustable high speed should be easier to tune.Let us know how things develope.

 

[tmcalavy]

Re: Installing a larger carb on my 55 SeaKing 12

Are you trying to boost hp with the bigger carb? If so, good luck.

 

[ohm116]

Re: Installing a larger carb on my 55 SeaKing 12

I was thinking it might give a bit more of a boost but it sounds like it wouldn't be much worth it. F_R I well be waiting to see what sort of results you get with your swap.

 

[F_R]

Re: Installing a larger carb on my 55 SeaKing 12

I was thinking it might give a bit more of a boost but it sounds like it wouldn't be much worth it. F_R I well be waiting to see what sort of results you get with your swap.

Well, as of right now after working on it for three days, it runs like a scalded dog at full throttle, and idles great. But anything in between, forget it.

 

[tmcalavy]

Re: Installing a larger carb on my 55 SeaKing 12

I dated a girl like that once.

 

[ohm116]

Re: Installing a larger carb on my 55 SeaKing 12

So essentially there is not enough adjust-ability for the mid range. Oh well, it was an idea.

I finally got a chance to try my motor with the external tank and apparently the pump works fine but I don't think I got all of the gas out of the carb the last time I ran it because it was a SOB to get started today, after it got going and cleared up it was fine. I ran it for a while and got it running even better then the last time and when I was done I just disconnected the fuel line from the tank and let it run out that way so hopefully it well start up better next time.

 

[F_R]

Re: Installing a larger carb on my 55 SeaKing 12

Progress report. I knew it wouldn't work, and it didn't. I spent at least 40 hours on this project and finally gave up and put the old parts back on it.

I made a customized intake manifold to accept the larger carburetor. That took a couple of days. Then I had to make a custom sync cam to open the throttle. That was good for another day.

Then in trying to get the mid-range to work, I had that stupid thing apart at least 50 times to modify the curve on the cam. Plus a trip to the lake to make sure it wasn't just my test tub setup.

Hey, it runs great with the old parts.