150 Johnson Speedo tube?

[maverick974]

I bought an Astroglass fish and ski a few weeks ago. Very happy with it so far. I'm fixing a few little things and one of them is the speedo. The way I understand it, the speedo tube goes down the middle leg of the engine and hooks up to the front of the leg somehow. I see a small hole but nothing to connect the speedo hose to.
1985 Johnson 150T.
Any suggestions?
One other question. If I cruise at say 3/4 throttle for one hour, how many gallons of fuel should I expect to use? In other words, what can I do to get the best economy out of this engine?

Thanks again, you guys are awesome.

 

[sutor623]

Re: 150 Johnson Speedo tube?

Not sure about speedo. Take HP of the motor, and divide by ten. That is how many gallons of fuel you will burn at open throttle in one hour, so 15 gallons an hour at WOT. The way to find the best "cruising" spot as far as gas mileage, is to take the cowling off the top of the motor, push the throttle to WOT (with motor not running) and then slowly pull the throttle lever back down. The best spot to keep it is right before the ignition starts to leave the most advanced position, and the throttle bodies start to close just a bit. Probably more like 7/8th throttle, or 15/16ths even. Probably only save a gallon or two per hour this way though.

 

[boobie]

Re: 150 Johnson Speedo tube?

There is a little nipple that is in the upper front of the g/c. It's normally just pressed in and that's where the speedo tube attaches to. Go to shop.evinrude.com, get in the parts section and you'll find it.

 

[Chris1956]

Re: 150 Johnson Speedo tube?

Most economical Cruise speed can vary by boat. A lot of boats will get the best efficiency at a small amount of speed above minimum planing speed. Running 7/8 throttle is better economy than running full throttle, but is usually less economical than running slower.

The best way to know is to do some tests. Run at 500RPM above minimum planing speed (usually about 3500RPM), and test fuel mileage. Repeat test at 3200RPM (provided she will plane) and at 4500RPM.

 

[maverick974]

Re: 150 Johnson Speedo tube?

Thanks guys,
I am going from an old Bayliner bass boat with an 85 hp engine to a 150 Johnson. I love the boat and engine and even the trailer. Easier to launch, the boat is a little larger so I can take more than 2 people if I desire and the 150 on the back is a screamer. It's really quick out of the hole.
Anyway, my biggest concern is how much fuel I'll use. With the old Bayliner, I'd put 5 gallons in the tank and I can cruise around all day on that with fuel to spare. It was an exceptionally economical engine but it was kind of slow. About 30 mph or so with 2 people and parts are prohibitively expensive when you can find them. Force parts are getting scarce for a 1985 engine.
So that's why the questions about economy of the 150. I'd rather go slower and be on the lake more than having a fast boat but only being able to afford to use it only now and then. I'm not rich by any standards so I gotta watch very closely my pennies.
Since we are on the topic of economy, would a higher pitched prop be more economical than a lower pitched prop? I got 2 props with the boat. A 17 pitch and a 24 pitch. I realize the 24 might be a bit much but I could sell that and get a 19 or 21 pitch.
What do you think?????

 

[Chris1956]

Re: 150 Johnson Speedo tube?

You really need an accurate techometer to figure out the correct prop pitch. Figure a 400RPM change for each 2" of pitch change on the prop. so rev your motor up to WOT with a std load and get the RPM. Now guess what prop you should choose to get the max RPM into the recommended range.

BTW -Your motor may have a rev limiter on it. This will not allow you to rev it higher than 6200RPM.

I run a 19" pitch on my 1998 Johnny 150HPV6, on a 21 foot Seaswirl Dual Console, but do not know if the gear ratio is the same on your motor.

 

[Silvertip]

Re: 150 Johnson Speedo tube?

The prop on a boat is like the transmission in your car but it only has one gear. so slapping on a prop with more pitch may actually cost you more fuel because you are lugging the engine. Making an engine run slower (lugging it) means the throttle needs to be open further to make up for that. More throttle = more fuel. To find the best prop you need to make several wide open throttle runs with what you consider an "average" load. Average meaning the way you will run the boat most of the time. When you make those runs note the WOT rpm on the tach. If the tach cannot get to the engine manufacturers recommended wide open throttle rpm (probably 5500 rpm) in your case, then the engine is lugging and you decrease pitch by 1 inch to increase revs 200 rpm. If the engine tends to rev higher than recommended then you are under propped and would increase pitch. But until you make those test runs you have no idea how you are set up. It may turn out the prop you have is the best. Now here is the kicker. Best economy and best performance will be with that dialed in prop. That's as good as it gets. If the prop is wrong at WOT it wrong across the entire RPM band.

 

[maverick974]

Re: 150 Johnson Speedo tube?

You really need an accurate techometer to figure out the correct prop pitch. Figure a 400RPM change for each 2" of pitch change on the prop. so rev your motor up to WOT with a std load and get the RPM. Now guess what prop you should choose to get the max RPM into the recommended range.

BTW -Your motor may have a rev limiter on it. This will not allow you to rev it higher than 6200RPM.

I run a 19" pitch on my 1998 Johnny 150HPV6, on a 21 foot Seaswirl Dual Console, but do not know if the gear ratio is the same on your motor.

The prop on a boat is like the transmission in your car but it only has one gear. so slapping on a prop with more pitch may actually cost you more fuel because you are lugging the engine. Making an engine run slower (lugging it) means the throttle needs to be open further to make up for that. More throttle = more fuel. To find the best prop you need to make several wide open throttle runs with what you consider an "average" load. Average meaning the way you will run the boat most of the time. When you make those runs note the WOT rpm on the tach. If the tach cannot get to the engine manufacturers recommended wide open throttle rpm (probably 5500 rpm) in your case, then the engine is lugging and you decrease pitch by 1 inch to increase revs 200 rpm. If the engine tends to rev higher than recommended then you are under propped and would increase pitch. But until you make those test runs you have no idea how you are set up. It may turn out the prop you have is the best. Now here is the kicker. Best economy and best performance will be with that dialed in prop. That's as good as it gets. If the prop is wrong at WOT it wrong across the entire RPM band.

Thanks guys. I got it. I'll try the 24 just to see where the RPMs are and go from there. No doubt the 24 will be too much but it will give me something to gauge what would be the correct prop.