1975 johnson 85 horse, need carburator adjustments

[Doyle Johnson]

can anyone help tell me the carb adjustment for my 1975 johnson 85 hose ? getting real bad gas milage.

Thanks !

 

[JB]

Re: 1975 johnson 85 horse, need carburator adjustments

Ahoy, Doyle.

Welcome to iboats.

Well, there is good news and there is bad news.

The good news is that the big JohnnyRude V4s of the 70s seem to last forever. Some guys refer to them as locomotives.

The bad news is that real bad gas mileage is a standard feature.

 

[ezmobee]

Re: 1975 johnson 85 horse, need carburator adjustments

Figure 8.5 gallons per hour at wide open throttle. I had a '73 85 and never found it to be overly thirsty.

 

[iwombat]

Re: 1975 johnson 85 horse, need carburator adjustments

The other news is those carbs have no adjustments to make. Fixed jets all the way around.

 

[F_R]

Re: 1975 johnson 85 horse, need carburator adjustments

The other news is those carbs have no adjustments to make. Fixed jets all the way around.

And the fixed jets are light years better than the adjustable carburetors that they replaced. Count your blessings.

While you are counting, consider this: That motor's distant ancestor was the beloved 1958 "Fat Fifty". Indestructable, but gulped 8-10 gallons per hour while making 50 horsepower. I'd say you are pretty good. The 50 had drain valves that dumped half it's gas overboard, your 85 no longer does that. So not only is it more efficient, it is greener too.

 

[rainman99]

Re: 1975 johnson 85 horse, need carburator adjustments

I have a 1985 90 HP Johnson. All you can do for best fuel useage is keep timing on mark and keep carbs in sync. and keep plugs clean. I get the best hours per. gal. runing 25-30 mph. about about 12 miles per gal.

Rainman

 

[Doyle Johnson]

Re: 1975 johnson 85 horse, need carburator adjustments

Thanks for the reply Guys........Found out there is NO carb adjustments and i have to live with this old gas Hog ! I only get 2 to 2 1/2 miles a gallon. Thanks for your replys and help.

Doyle

 

[F_R]

Re: 1975 johnson 85 horse, need carburator adjustments

Thanks for the reply Guys........Found out there is NO carb adjustments and i have to live with this old gas Hog ! I only get 2 to 2 1/2 miles a gallon. Thanks for your replys and help.

Doyle

Oh come on, only 2 MPG? There is more to this than meets the eye. At what speed? And what boat?

 

[GeneH]

Re: 1975 johnson 85 horse, need carburator adjustments

Careful check of the timing and sync and is the prop mated correctly to the boat you are moving, or is it a barge?

 

[Doyle Johnson]

Re: 1975 johnson 85 horse, need carburator adjustments

My Boat is a 1973, 17.3 Ft, Robalo Center consol. Heavy boat but i really like it. Once the motor is warmed up, the timing seems like it's right on the money. Answer to the question, at full throttle i only went 15 miles and the 6 gallon tank went empty.......Bummer !

After the first of the year, I like to find a motor maybe a 100 horse or better Johnson that gets better gas milage and sell the 85 Horse. Have a great Christmas all and thanks !

 

[rodbolt]

Re: 1975 johnson 85 horse, need carburator adjustments

15 miles on 6 gallons with that motor is great.
at 3800 RPM and 30MPH with a 21 seapro with a tower and a second station my F150 Yamaha will burn 6 gallons in 22 miles.
your antique 85 2 stroke isnt that for off my 2007 EFI fourstroke.
yes, I owned a 58 fifty only thing could burn more gas is the about 1964 75 starflite we replaced it with.
and this was back in the early 80s when gas seemed cheaper.

 

[ezeke]

Re: 1975 johnson 85 horse, need carburator adjustments

I think that your boat was rated for 140HP so the 85HP motor is asking a lot. You could probably get good fundamentals with a 13 pitch prop but your top end won't be great.

 

[Joe Reeves]

Re: 1975 johnson 85 horse, need carburator adjustments

That engine has what is called "Crusing Range"....... a slight loss of top speed but a vast savings on fuel, accomplished when the throttle is retarded somewhat BUT the timing is left at full spark advance, as follows.

Keeping it simple, accomplished by taking the engine to full throttle, then backing off to approximately 3/4 throttle.

You can see this feature for yourself with the engine NOT RUNNING. Have the hood off and have someone spin the prop while you put the engine into forward gear. Observe the spark advance (timer base under the flywheel) and the throttle butterflies as you take the throttle to absolute full throttle.

Now...... slowly back off the throttle, again observing the spark advance and throttle butterflies. You'll notice that the throttle butterflies start to retard immediately BUT the spark advance does not.

When you see that the spark advance starts to retard...... there is your crusing range setting.

I did a test many years ago with a V4. Full throttle used 6 gal of fuel in 45 minutes. At crusing range, 6 gal lasted 1 hour and 45 minutes. Let us know what difference you encounter.

 

[F_R]

Re: 1975 johnson 85 horse, need carburator adjustments

That engine has what is called "Crusing Range"....... a slight loss of top speed but a vast savings on fuel, accomplished when the throttle is retarded somewhat BUT the timing is left at full spark advance, as follows.

Keeping it simple, accomplished by taking the engine to full throttle, then backing off to approximately 3/4 throttle.

You can see this feature for yourself with the engine NOT RUNNING. Have the hood off and have someone spin the prop while you put the engine into forward gear. Observe the spark advance (timer base under the flywheel) and the throttle butterflies as you take the throttle to absolute full throttle.

Now...... slowly back off the throttle, again observing the spark advance and throttle butterflies. You'll notice that the throttle butterflies start to retard immediately BUT the spark advance does not.

When you see that the spark advance starts to retard...... there is your crusing range setting.

I did a test many years ago with a V4. Full throttle used 6 gal of fuel in 45 minutes. At crusing range, 6 gal lasted 1 hour and 45 minutes. Let us know what difference you encounter.

Agreed. Only problem is if the boat is underpowered, and starts to settle in the water (comes off plane) when you back off to the cruising range. If that happens, the mileage will probably get worse instead of better.

 

[Joe Reeves]

Re: 1975 johnson 85 horse, need carburator adjustments

FR.... Yep, the rig must stay on plane to possess the crusing range advantage.