# Speed w/ 1966 Johnson 20 HP



## Ictalurus (Mar 8, 2011)

I have this question in my motor thread, but thought I might get some new looks with a fresh post. I recently bought a 1966 Johnson 20 HP motor, which is a nice upgrade from my 8 HP. My boat is a 1440 MV and with about 180 lbs of mods, two people, gear & full livewell it hit 21.6 MPH wide open on the GPS. That was max, usually clocked about 20.7. That seems pretty good for a '66. The boat got up on plane at or near 13 MPH. Went through about 3 gallons, the GPS logged 12.3 miles, some of those were drifting and trolling through the cypress stumps though. So, the mileage may not be all that bad. I'm just used to dinking around on a 170 acre lake with a 5 mph speed limit, when I hit a bigger lake and opened it up a bit she drank a little more fuel than I'm used to. I also added a can of Sea-Foam to the tank. 

The good news is the motor seems to run great and starts right up. Every once in awhile it seems to have a small hiccup at idle, almost sounds like a miss. Not sure if I need to do anything for this or not. Just wanted to see if the speed sounds about right to everyone.


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## crazymanme2 (Mar 8, 2011)

The speed sounds about right.

The hiccup sounds like a little lean.Richen it up just a touch until it goes away.


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## Ictalurus (Mar 8, 2011)

crazymanme2 said:


> The speed sounds about right.
> 
> The hiccup sounds like a little lean.Richen it up just a touch until it goes away.



Thanks crazymanme2, I'll play with the rich lean knob a bit, I've never had one on a motor before so the adjustment is new to me. Also, would I expect to see much a speed increase with just me in the boat and no gear?


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## flintcreek (Mar 8, 2011)

Sounds about right. I had a 66 20hp on a 14' Crosby Sled (light weight fiberglass boat) and it ran 22 with me and my son and gear. With just one smaller person in it the 20 hp would push it about 30. I would guess you will pick up 6 to 8 miles per hour with one person in the boat. The 66 Model is one of my favorite Johnson motors. I believe I have had 3 in the past 10 years.

Flintcreek


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## Pappy (Mar 8, 2011)

Okay - Only comparison I have again is my 18, which will have to do. On my 8.71 mile trip I burned a little over a gallon so lets say it was 1.2 gallons. You ran 12.3 miles on approx. 3 gallons. Mine averaged out to 7.25mpg. Yours was 4.1mpg. That is a difference of around 3.15mpg or around 43% fewer mpg. Quite a difference. At or near WOT it would make no difference whether you were pushing a barge or a lightweight hydro your fuel burn would be the same but your mileage would vary. In other words the weight, the placement of the weight, and the type and condition of the hull may be what is killing your mileage. I cannot remember whether or not your engine has a high speed adjustment on the carburetor. If it does then take it to WOT and turn it clockwise until the engine peaks out RPMwise and then back it back out around 1/8 turn to give it a cushion of fuel. If not, check the condition of your prop. Compare it to a new one or at least a couple of other props to see if yours has been worn down from sandbars, etc. A little bit or wear can make a drastic difference in mileage and performance. As I mentioned before, you can check the high speed jet if you have one and see if it is the correct one for your engine. You will either have a high speed jet or an adjustment knob (not the one for the idle mixture adjustment). Good luck!


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## Ictalurus (Mar 9, 2011)

Pappy said:


> I cannot remember whether or not your engine has a high speed adjustment on the carburetor.



Pappy, thanks again for the input. I'm not trying to gain speed or tweak too much, just want to make sure my motor is top shape and running true. I've attached an exploding diagram of the carb for the 20 HP, could you/someone point out the high speed adjustment. Also, do I need some type of tachometer, or just go by sound? The prop is in decent shape, not great. Add props to the list of things I need to know more about. What would you guys recommend as a replacement prop for this beast. Thanks again.


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## PartsMan (Mar 9, 2011)

Sounds about right to me. My 1655 went 19 by myself.


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## BaitCaster (Mar 9, 2011)

Don't know if this helps but my 18hp Fastwin pushes my 1542 at around 23 mph at WOT with just me and my gear in the boat. I'm thinking I may pick up 1 or 2 mph now that the carb has been cleaned out over the winter.


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## Ictalurus (Mar 9, 2011)

flintcreek said:


> Sounds about right. I had a 66 20hp on a 14' Crosby Sled (light weight fiberglass boat) and it ran 22 with me and my son and gear. With just one smaller person in it the 20 hp would push it about 30. I would guess you will pick up 6 to 8 miles per hour with one person in the boat. The 66 Model is one of my favorite Johnson motors. I believe I have had 3 in the past 10 years.



Thanks man, hope you went through three of them because you liked them. :lol: I'll clock it with just me and no gear in there and see how she does.



BaitCaster said:


> Don't know if this helps but my 18hp Fastwin pushes my 1542 at around 23 mph at WOT with just me and my gear in the boat. I'm thinking I may pick up 1 or 2 mph now that the carb has been cleaned out over the winter.



That helps, looks like your boat may weigh less w/out the decks and such. I think I'm right about where I should be. Baitcaster, did you do the carb yourself? I may order a carb kit and tackle that when the fishing slows.


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## BaitCaster (Mar 9, 2011)

Ictalurus said:


> That helps, looks like your boat may weigh less w/out the decks and such. I think I'm right about where I should be. Baitcaster, did you do the carb yourself? I may order a carb kit and tackle that when the fishing slows.



No, when it comes to motors of any kind I am mechanically disadvantaged! Had my mechanic do it.


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## flintcreek (Mar 9, 2011)

The old 18's and 20's are my favorite motors. I still have a 58 Johnson 18 hp, 58 Evinrude 18 hp, 56 Johnson 15 hp and 68 20 hp. They are the easiest motors to work on and light for the amount of power along with parts being reasonable. If I remember right and you have the right diagram the fast speed jet is not adjustable. I believe the high speed jet is number 79 and number 80 is just a bolt with extension for the knob that comes through the housing and has a slow speed knob and linkage that fits over the extension part. The high speed on the 66 is not adjustable. These carbs are very easy to rebuild and there are some real good articles on the net. Good Luck.

Flintcreek


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## Pappy (Mar 9, 2011)

Flintcreek is absolutely correct. As luck would have it I had a 1966 Johnson 20hp come into the shop today for a gearcase re-seal. Had a chance to look at the carb set up after finishing up the job. No high speed adjustment.


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## Ictalurus (Mar 10, 2011)

flintcreek said:


> The old 18's and 20's are my favorite motors. I still have a 58 Johnson 18 hp, 58 Evinrude 18 hp, 56 Johnson 15 hp and 68 20 hp. They are the easiest motors to work on and light for the amount of power along with parts being reasonable. If I remember right and you have the right diagram the fast speed jet is not adjustable. I believe the high speed jet is number 79 and number 80 is just a bolt with extension for the knob that comes through the housing and has a slow speed knob and linkage that fits over the extension part. The high speed on the 66 is not adjustable. These carbs are very easy to rebuild and there are some real good articles on the net. Good Luck.
> 
> Flintcreek





Pappy said:


> Flintcreek is absolutely correct. As luck would have it I had a 1966 Johnson 20hp come into the shop today for a gearcase re-seal. Had a chance to look at the carb set up after finishing up the job. No high speed adjustment.



Thanks guys, just the info I needed. So far so good with the motor, this is my first spring with it and with the motor being a '66 I want to make sure everything sounds good to the motor guys. I'll order a carb kit and take that on later in the year, sounds like a great project to learn from. Thanks again, I'd never have bought this without the resources here :lol:


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## PartsMan (Mar 10, 2011)

BaitCaster said:


> Don't know if this helps but my 18hp Fastwin pushes my 1542 at around 23 mph at WOT with just me and my gear in the boat. I'm thinking I may pick up 1 or 2 mph now that the carb has been cleaned out over the winter.



What prop are you running?


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