Will different jets improve performance?

[John Lapic]

I am pulling out of moth balls a 1971 Johnson 9.5 that I had some 35 years ago when I was a kid. At WOT, it does not seem to achieve the same RPM as I recall it did as a kid. The big difference between now and then, besides more weight and grey hair, is a change in altitude. Originally the motor was used at 1300 ft. I just brought it to an altitude of 6000 ft. Will changing jets improve performance and if so, how do I determine the right jet for my altitude?

 

[CATransplant]

Re: Will different jets improve performance?

All gasoline engines lose power at high altitudes. You don't need new jets, though. You should be able to adjust the mixture with the needles to compensate, at least partly, for the change in altitude.

Also, you may have to change to a slightly lower pitch prop to get the rpms up to the normal range.

I can't remember whether the 9.5s have both jets adjustable or not.

Also, after that long layup, you probably will benefit from a good carb cleaning and kitting. Change the water pump impeller, too, if you haven't already.

 

[John Lapic]

Re: Will different jets improve performance?

I did rebuild the carb and changed the impellor. Low speed jet is adjustable, high speed jet (where I am having trouble) is not..........

 

[CATransplant]

Re: Will different jets improve performance?

Looking at the parts blowup on your carburetor, it looks like that jet is not even replaceable, nor are there alternative sizes. Worse, there seems to be just one prop available for that outboard, and that's the standard 8 pitch. I even checked other makers.

The 9.5 is sort of an odd duck for Johnson/Evinrude, which seems to have decided that they never really made that model or wish they hadn't.

I suspect that you're pretty much stuck with it as it is. It just doesn't look like there are many options for operating it at higher altitudes.

I don't have, nor have I had that outboard, so I'm limited to researching it in the parts blowup. It may be that you can alter the timing somewhat, but I'm not sure that will have the effect you are looking for.

Maybe someone will chime in who has more experience with it. I'm out of ideas.

 

[John Lapic]

Re: Will different jets improve performance?

Actually the high speed jet is replaceable. It is located behind the carb drain plug. I had it out when I rebuilt the carb. That's why I thought re-jetting may be possible

 

[tashasdaddy]

Re: Will different jets improve performance?

you really need to talk to a evinrude/johnson dealer in your area. yes rejetting will help you. the air has less oxygen content. so you need more air, for proper combustion, but it can also lean out the oil,fuel and air mixture, and not lubricate properly. you need the correct jet and mixture.