motor change

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115johnson78

Petty Officer 3rd Class
Joined
Jul 8, 2009
Messages
81
I currently have a 1978 Johnson 115hp, it has two cylinders that are low in compression. I have found a 1978 Johnson 140 hp power head that is good. I was wondering just how much of the parts would inter change. My biggest concern is are the carbs gona work. Any answers would help. Thanks.
 
S

splitshot

Petty Officer 1st Class
Joined
Feb 10, 2008
Messages
251
Re: motor change

the 140 your getting doesnt have the carbs ?? if it does use them, i believe the only difference between a 115 and a 140 is the bigger exhaust on the 140 and bigger carbs i believe...make sure the shift linkage is the same (make sure the new power head has the hole where your shift linkage is bolted and you should be good) but others will chime in with more info i'm sure
 
1

115johnson78

Petty Officer 3rd Class
Joined
Jul 8, 2009
Messages
81
Re: motor change

Thanks for all the info. david r that website link has a lot of info. Just so you know i did what you said and look for every nut and bolt lol. On the carbs the only diff i found is that it showed different orfice plugs for the 115 and the 140. On the 115 it showed a idle orfice would those b the jets.

Splitshot no dont have the carbs.

I was wondering do you think by adding more hp a diff prop would be in order?
My boat is a 1978 Invader Deep V Bow Rider. Any suggestions on wich direction to go.
 
david_r

david_r

Lieutenant Junior Grade
Joined
Aug 11, 2008
Messages
1,118
Re: motor change

i have lots more of those kinds of links if you need some more.

as far as the prop goes i would hook it all up just like it is and see where your rpms fall .................... more than likely you will be able to go up a lil in pitch, that will give you more top end....... a little anyways. ive been told unless you up your hp by at least 50% you wont notice much of a difference...........

those props are pricey....... well stainless are.
 
1

115johnson78

Petty Officer 3rd Class
Joined
Jul 8, 2009
Messages
81
Re: motor change

what is the diff between a flat back and a buble back. will they still swap out. my 115 is a flat back. thanks
 
C

crb478

Lieutenant Junior Grade
Joined
Dec 6, 2006
Messages
1,036
Re: motor change

The bubble back is more of a high flow exhaust system and has better porting. If you are switching powerheads just keep the bubble back on it and switch to the larger jets in your carbs. Only downside to the bubble back is if you need to change thermostats so it would be a geat time to do it now while everything is accessable.
 
1

115johnson78

Petty Officer 3rd Class
Joined
Jul 8, 2009
Messages
81
Re: motor change

Thanks all for the info. I still cant believe how much info is on here. This is awsome.
 
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