1973 Johnson 65hp pole # question.

[Basszilla4]

Hello,

Sorry to pester you all with another newbie question. Just got (new to me) boat legal and on the water for first time. 1984 18ft Grumman aluminum flat bottom with 1973 65hp Johnson 3 cylinder. Runs like brand new. Only problem, was not original motor for boat. There is more power than for the weight of boat. When going to WOT, boat reaches top speed in seconds. Have to back off because it seems to over-rev motor. Looking into buying a higher pitch prop to fix this problem. On there now is a 13 3/4 x 15. Seems to be waisting power.

Doing research, I find the magical rpm's for this motor is between 4500 - 5500 at WOT. So, before I spend big bucks on a prop, would like to get a tachometer. Been told rpm's is how to determine prop selection. Not too high, not too low.

My question is, what is a pole on my motor and how many do I have or need? Or, can a tachometer even be hooked up to this 2 stroke engine? In my research, I found I might have a 12 pole. If so, how many pole tach should I buy and how do you install? I have hooked up tachometers in cars before, but never on a outboard.

Thank you in advance for any info that might help.

Sincerely,
Errol (Basszilla4)

 

[Basszilla4]

Re: 1973 Johnson 65hp pole # question.

Looking at a 17" pitch or even a 19". I read that going up a size in pitch will drop rpm's by 200. Until I have a tach, I would not know how much over-rev I am achieving. Any suggestions on these pitch sizes would be appreciated also. Thanks again.

Sincerely,
Errol (Basszilla4)

 

[Benny1963]

Re: 1973 Johnson 65hp pole # question.

you need to make sure your tach is right before you buy a prop
also mark a line across you prop hub before you put it back in water
to see if you have a hub slipping .on your prop what kind of mph are you getting is it planeing

 

[Basszilla4]

Re: 1973 Johnson 65hp pole # question.

I am on plane within 20 feet. Way before I get to WOT. Now, I hammer down throttle until I get on plane, like 3 seconds. Then back off throttle so I just stay on plane. I can cut throttle about halfway and still stay on plane. From halfway to WOT, I don't gain hardly any speed. Runs 30 - 35mph.

Don't have a tachometer yet. At WOT, the engine is screaming. Don't want to over-rev engine and do any damage. Was wanting to buy a tachometer first so I could monitor engine rpm's before "guessing" at a prop selection. Having troubles figuring out how many poles my engine has so I can make sure I am getting the right tachometer for my engine. No hub slipping that I can tell. Will try drawing line on hub next time I launch boat.

Any ideas on number of poles my 73 Johnson 65hp 3cylinder has? Don't know if this matters, but its a PowerShift II, Loop Charged. These are the markings on engine cover.

Thanks again.
Sincerely,
Errol (Basszilla4)

 

[Reggie08]

Re: 1973 Johnson 65hp pole # question.

To check your rpm's, it might be easier and quicker (and probably cheaper) to find a Tiny-Tach. There's no need to know what pole setting you need or cutting holes in dash, etc. You can simply tape it to the motor and wrap the wire around the spark plug wire.

 

[guy74]

Re: 1973 Johnson 65hp pole # question.

I think it is a 12 pole alternator, thats what my 1988 60hp 3cylinder motor is. I'm sure you would be able to over rev the motor on a light weight boat, especially a flatbottom, with that prop. I use that same prop on my trihull with the 60hp, I can get 6000 rpms, at around 34 mph with the heavier fiberglass boat.

 

[Basszilla4]

Re: 1973 Johnson 65hp pole # question.

Ahh, but I am a gauge looking at kinda guy. I like knowing what my engine is doing no matter what. Looking to buy duel battery gauges, tach, water/engine temp and pressure (if applicable for my engine) and any other little gismo gauges I could buy. Was planning a tach purchase even before I thought of needing a steeper pitched prop. Just need to know how many pole alternator or magneto I have. After installing a tachometer, I will post another thread on selecting prop. Until rpm's are determined, will hold off on prop. There are some real nice tach's here on this site. Hopefully one will work with my motor.

Thanks again.
Sincerely,
Errol (Basszilla4)

 

[Basszilla4]

Re: 1973 Johnson 65hp pole # question.

I think it is a 12 pole alternator, thats what my 1988 60hp 3cylinder motor is. I'm sure you would be able to over rev the motor on a light weight boat, especially a flatbottom, with that prop. I use that same prop on my trihull with the 60hp, I can get 6000 rpms, at around 34 mph with the heavier fiberglass boat.

Yes, I knew that the prop size was wrong. If you were getting 6000 rpm on a heavy fiberglass trihull, I know I can blow my engine sky high. I think I would be able to judge prop size after knowing how much over-rev I am getting. Meaning, if I am pegging 7000+ rpm's, then I need a prop at least two sizes bigger, maybe even three. If the rule of thumb hold true. For every size increase, you drop 200 rpm"s. So going from a 15" to a 17" should drop rpm's by 400. I'm sure there is more to it than that, but its a start for a mechanically inclined boating newbie...lol

Thanks again everybody.

 

[ezeke]

Re: 1973 Johnson 65hp pole # question.

12 poles 6P setting on the Teleflex and OMC tachs is correct for all but some 2 cylinder models: See page 4 for the Teleflex chart:

http://ww2.tflx.com/PDF/99320.pdf

 

[guy74]

Re: 1973 Johnson 65hp pole # question.

Where are you located at? You might want to include your location in your profile. If you were some where close by I have 17" and 19" pitch props that would fit your motor that you could try, before buying one of your own.

 

[Basszilla4]

Re: 1973 Johnson 65hp pole # question.

Where are you located at? You might want to include your location in your profile. If you were some where close by I have 17" and 19" pitch props that would fit your motor that you could try, before buying one of your own.

Located in Ottawa IL. About 90 miles SW of Chicago. Sorry, havent gotten to updating my profile yet. I can see I like this website and will probably be visiting here a lot now I am the boat owner.

Not a total moron when I comes to boats. My step-father is a member of a local boat club named Shorline Boat Club. He is the commissioner, or something like that. He owns a 35 foot cuddy cabin with twin 350 Mercruisers. I call it a small yacht. Absolutely gorgeous. I had asked him on the prop and tach questions and well, he sent me to the internet. So, here I am...lol

Are either one of those props a 13 spline?