prop suggestion for johnson 9.5

[pafree]

i have a 14' foot Loweline square johnboat. it has some decking and floor boards. i have a 6 gallon fuel tank and rear mount trolling motor and battery mounted in middle of the boat. it has a good running 1969 johnson 9.5 with a 8x7 prop that is beatup from oystershell reefs and debris for IKE. i use the boat for fishing the back/marsh waters and checking trot and sail lines. it is usually me (big boy) with a monster(kid) or two with poles, tackle box, and baitbucket ( bigger bait cooler when running lines.)

right now the motor runs great but has a uneven vibration when running down the channel. i just replaced the lower unit oil and all fuel lines and cleaned carb. it also has good spark cold and after warmed up. i want to replace the prop with a new one and was thinking about the 8x6 1/2. from looking at a chart, this is the heavy load prop where the 8x7 1/2 is the cruising one. would it make a difference? any advice is welcome. thanks.

 

[hwsiii]

Re: prop suggestion for johnson 9.5

Free, how many RPM are you turning and how fast do you go at wide open throttle.


H

 

[pafree]

Re: prop suggestion for johnson 9.5

sorry but no way to judge RPMs except by ear. the prop does move the boat against wind and current but not much better than the trolling motor. at wide open throttle the bow rises but it doesnt move much faster. last week i found/fixed a couple of fuel leaks along the fuel line and motor does have a increase in RPMs now after the fix but that is in a flushing bucket and has not been tested on the waterway. i also have moved some of the heavier equipment to the bow of the boat to see if this would help. i plan to go for a ride next week. these tests were done with motor trimmed all the way down and this is the correct length shaft motor for the boat. i was wondering if the smaller prop would give me a more bulldog pull effect over a weak jackrabbit under a heavy load.

 

[hwsiii]

Re: prop suggestion for johnson 9.5

Free, it is cheaper to buy a Tiny Tach for $ 50 and be able to know what prop to buy than guessing in the dark without real numbers and a base to work from. It can also let you know in the furture if you have problems because you will lose RPM for no apparent reason.
A change from the 7.5" pitch to a 6.5" pitch is almost 800 RPM difference and that may be right or it may be wrong, you don't know beause you don't have a tach. I am not trying to berate you, just hope this makes you realize you need a tach, even for smaller motors.


H

 

[pafree]

Re: prop suggestion for johnson 9.5

the Tiny Tach is a great ideal. i went to their website and i am not sure which one to get. being kinda new to outboards, which one do i need. is my motor classed as a two stroke because it uses premix. educate me please. it does have two cylinders.

 

[hwsiii]

Re: prop suggestion for johnson 9.5

Your motor is a two stroke, they make one that just gives you the RPM and then they make a better one that atually gives you engine hours and timers to keep up with service intervals for changing impellers and tuneups. Buy whichever one you want, just be sure two stroke.


H