80hp is only getting 7mph .. too slow any ideas?

[Bosunsmate]

Re: 80hp is only getting 7mph .. too slow any ideas?

Yep try new plugs and feel the heads for heat differences too, they should be relatively even.
I dont know the adjustment for those screws on that one so cant comment on that sorry, but its good that removing those plugs does cause engine changes.
You could try that on the left too and cylinder by cylinder to see if any arent doing a thing

 

[lbcboating]

Re: 80hp is only getting 7mph .. too slow any ideas?

I fixed it! New spark plugs. Huge difference. I suppose the old ones were bad. I took the throttle up barely 75% and it felt like I was already pushing 40mph .. I didn't bring the throttle all the way up tho because i'm using NGK B6S spark plugs which I was told would work on this motor but they are listed for a Johnson 35 hp. Wouldn't these run too hot for an 80hp?

The NGK Plug recommended online for an 80hp Johnson for the same year was a B8S, or a Champion J4C or J6C.. All which are hard to find.. The old spark plugs that were in there when I got it where Champion J6C.

The guy I got the boat from said although it's an 80HP, he thinks his grandfather might modified something with the outboard because he said it felt more like a 150HP. If that were the case shouldn't I use a different plug that can handle more heat as this could have what destroyed the spark plugs already in there?

 

[Bosunsmate]

Re: 80hp is only getting 7mph .. too slow any ideas?

Id use whats recommended, even if you have to ring around to get them, bigger motor does not necessarily mean more heat.
Congrats on getting it running good again

 

[Vic.S]

Re: 80hp is only getting 7mph .. too slow any ideas?

I fixed it! New spark plugs. Huge difference. I suppose the old ones were bad. I took the throttle up barely 75% and it felt like I was already pushing 40mph .. I didn't bring the throttle all the way up tho because i'm using NGK B6S spark plugs which I was told would work on this motor but they are listed for a Johnson 35 hp. Wouldn't these run too hot for an 80hp?

The NGK Plug recommended online for an 80hp Johnson for the same year was a B8S, or a Champion J4C or J6C.. All which are hard to find.. The old spark plugs that were in there when I got it where Champion J6C.

The guy I got the boat from said although it's an 80HP, he thinks his grandfather might modified something with the outboard because he said it felt more like a 150HP. If that were the case shouldn't I use a different plug that can handle more heat as this could have what destroyed the spark plugs already in there?

The officially recommended plugs for that engine are J4C you should stick with these if at all possible. If you think the plugs are overheating you do not want to be changing to J6C because these are hotter. Perhaps you should be looking a the fuel/air mixture and carb adjustment.

If you really must use NGK plugs the equivalent of J4C is B7S. (B6S is the equivalent of J6C.) Note the numbering runs the opposite way in NGK plugs. High numbers in Champion plugs are hotter but high numbers in NGK are cooler so B8S is an even cooler plug than B7S.

Most of the main brands of outboard in the world use NGK plugs but Champions are now recommended for all Johnsons and Evinrudes except some of the most recent. I believe the prejudice against NGK may be due to the unsuitability of resistor suppressed plugs for early OMC CDI ignition systems. Inductively suppressed plugs ( Champions beginning with a "Q" ) were developed for use with these but NGK resistor suppressed plugs were often, and still are, quoted as equivalents. They are not and lead to poor performance. However none of this is relevant to your 80hp engine.

J4C (and J6C) are common plugs in older OMC engines so should not be difficult to obtain.