What is a good speed for my Johnson 140?

[imported_airxsteel]

I have a 79 Johnson and wanted to know what kinda speed should I be looking at. I have had it open throttle on a full load on a 16 ft fiberglass, and it was at 45 mph (GPS).

Is that normal on a full load? I am not sure what the prop is. I want to to say 12 , and I know it is aluminum.

I have no jackplate either.

What range of speeds should I be getting?

Thanks,
Eric

 

[JB]

Re: What is a good speed for my Johnson 140?

What is the weight, ready to launch, and what sort of bottom shape does it have?

 

[imported_airxsteel]

Re: What is a good speed for my Johnson 140?

Well the max capacity rating is a 150 HP , and 5 persons with 860 pounds. I have no idea what it weighs.

Here is a picture of it. It is an 82 Kingfisher, 16ft boat.

 

[Dhadley]

Re: What is a good speed for my Johnson 140?

If the boat has a pad you should be able to do slightly better. If not then you're about right. We assume not since there is no jackplate.

We have the GPS speed so if we knew the prop pitch and top rpm we can calculate the slip %. That way we know where we're at. It'd help to know what brand and type of prop also.

 

[imported_airxsteel]

Re: What is a good speed for my Johnson 140?

Aluminum standard OMC prop , I think
389512

12 3/4 X 21

Don't know the RPM's, my tach is busted. I need to get another one hooked up to it. I have that in another post
d

 

[Dhadley]

Re: What is a good speed for my Johnson 140?

Assuming you're turning 5500 you'll be at just under 20% slip. We can do much better than that. If you're at 5000 rpm you're at about 11% slip. That's good on slip but bad on rpm. Again, we can do better. That just gives you an idea of how important it is to know the rpm.

We'll get you going. Get the tach working and we'll go from there.

 

[imported_airxsteel]

Re: What is a good speed for my Johnson 140?

Thank you very much. That is very nice of you guys.
I appreciate the openess of communication and learning on this site. Always a great place to get information.

Thanks again,
Eric

 

[Thumpbass]

Re: What is a good speed for my Johnson 140?

just for reference, I have a 15.5' tri hull bass boat that had a '79 Johnson 100hp on it. The motor had 7psi on one cylinder (broken rings) and still pushed the boat 43 mph (GPS) at 5300 rpms (13X19 SS prop). I have recently replaced the motor with a rebuilt '78 85hp Johnson and it pushes the boat 41mph at 5200rpms with the same prop (and load). I since have bought a 17p prop to raise the rpms. Any way I figured I'd chime in since the our boats are some what similar and both have (had) late 70's v-4 cross flows.

 

[Dhadley]

Re: What is a good speed for my Johnson 140?

Dropping pitch to gain rpm is only a last (very last) resort. Work the set up before you change props. Lots less $$$.

 

[Texasmark]

Re: What is a good speed for my Johnson 140?

Looks a lot like a Skeeter (brand) Wrangler hull of the gass crunch era.....'75 ish. Friend bought one and brought it to work to show it off to his buddies. Don't remember if the engine was 150 or 175. The little boat could handle the HP for it's length.

They got mad at him because we had gas lines then and they said that they didn't want have "their" gas rationed and have to wait in line because of a boat.

Saw a few of them on the lakes. Don't have any specs on hp vs speed, but they were padded and had the lifting strakes to get you on there and when hooked up there wasn't much boat or pad in the water and the rooster tail and all was just fine mist..(which says they were doing at least 45 for my guess)..the deep V was unusual for Skeeter at the time and allowed for smooth navigating (at lower speeds of course) on our large lakes where the wind is always blowing and big waves are usually the norm in the open areas.

Did notice that your alum prop is cupped when you'all get through talking about setup and start talking about HP props and pitch and all

Didn't mean to butt in. Just passing time and sharing experiences.

Mark

 

[Theoutdoorsman]

Re: What is a good speed for my Johnson 140?

Eric, I have a 17 1/2 foot '79 Maidencraft powered by a '79 E'rude 140. I'm turning an OMC 384142 19" pitch steel wheel with a double cup. My top end speed is 51 mph at 5900 rpm's. I had similar top end speeds as you are stating before changing to the double cupped prop. It truely made all the difference in the world on my rig. Now it doesn't blow out before full trim. The ride I have now is about as nice as I could have hoped for. It gave me a great hole shot and an impressive top end with lots of lift. Paid around $100 for the prop on ebay, and that includes shipping. Others will chime in and steer you in the right direction. Be patient. Good luck.............ALAN

P.S...... Still running great since the rebuild. Thanks again Dhadley!!!

 

[imported_airxsteel]

Re: What is a good speed for my Johnson 140?

As Jim Carey would say in the movie "Dumb and Dumber"

"So you're saying theres a chance......YES!!!!!"

 

[imported_airxsteel]

Re: What is a good speed for my Johnson 140?

Ok, I took it out this weekend with a less than full load. I took out alot of weight like fishing seats, which those weigh a ton anyway. Took out the spare prop, transom saver, tie downs, and all the extra stuff I don't use.

Just me and my fishing stuff on 12 gallons of gas and two batteries. Pretty calm water, got it up to 51 MPH on the GPS. It is amazing how weight in the boat can increase your speed like that. I gained 6 MPH just by dumping all that stuff, (and a bunch of kids)....HA!!

 

[flabum]

Re: What is a good speed for my Johnson 140?

I have a 16 Baja with a 1978 140 that was just touching 58 mPH with the wrong prop and melted exhaust filler blocks:

 

[imported_airxsteel]

Re: What is a good speed for my Johnson 140?

OUCH.....HOLY S**T !!!

Guess I will ease up on the old throttle then. What does the exhaust filler blocks do, and what are they made up of if they burn up? Are they gaskets or something around it or actual metal?

 

[rdcinmn]

Re: What is a good speed for my Johnson 140?

I noticed what appears to be a regular steel cotter pin on your prop nut, you might want to change that to a stainless steel cotter pin.

When the steel rusts away the prop will be easy to find - but not the nut & washer:$

 

[imported_airxsteel]

Re: What is a good speed for my Johnson 140?

Never heard of that, but makes sense. Where can I get one?