Fuel Selection for 82 150HP Johnson

[jarway]

Finally got the power issue figured out with my motor(Mod #J150TLCNM and S/N J5699966). Turned out to be a couple of pieces of foam rubber (probably from the cowling insulation and I don't know how that ended up in the fuel line and got past the filter screens on the the motor)) stuck in the jets in the top carb. Runs smooth now (5200 RPM at WOT with a 19 pitch prop trimed up-- may try a 17) and I was reading the shop Manual and noticed the the recommended gas for a "1973 - 1985 135-235 HP motor is 91 octane or greater." It goes on to say that if you use 88, then max spark plug advance must be reduced 4 degrees except on 1983-1985 XP and GT models. If octane less than 86 is used, it is recommended to consult dealer about engine modifications. I just caught this and have been running 87 octane (regular gasoline) in the motor and it seems to run fine.

Should I switch to high test since I don't want to do any harm running the lower octane but at the same time with gas prices the way they are, I want to try to stay semi-economical (yeh I know it's a boat) with fuel.

Any advice would be appreciated.

 

[DJ]

Re: Fuel Selection for 82 150HP Johnson

5500 RPM is too low. Should turn 5500-minimum.

Todays 87 octane is fine.

 

[jarway]

Re: Fuel Selection for 82 150HP Johnson

Thanks djohns19. I had wondered if the recommendation in the Shop Manual was based on old gasoline specs. I realize 5200 rpms is too low which is why I am thinking about a 17 pitch prop. Should gain 400 to 600 rpms since I tested one out when the motor was running badly and it made a difference. Any other suggestions about getting the WOT rpms up a little more?

 

[DJ]

Re: Fuel Selection for 82 150HP Johnson

jarway,

Remember this.

One inch in prop. will usually net 200 RPM, up or down.

 

[jarway]

Re: Fuel Selection for 82 150HP Johnson

10-4 So if I go with a 17 pitch, I should gain 400 rpms which would put me at around 5600 rpms which is where I believe I want to be. I wanted to get a spare prop anyway but I have a new SS 19 pitch so I may go with a 17 Aluminum until I see how performance plays out.

Thanks again.