Used boat new to me with banged up prop

[DrinkingEmu]

- 1st year of boating, many questions, not sure of part names.<br />- '92 40 hp Johnson model TJ40ELENM on 17 ft aluminum Tracker tx17<br />- fishing will be main use<br />- not sure of prop number that is on it now <br />- I was told it is a "Michigan" 17 pitch, but I do not remember the diam.(can't read numbers)(on the prop that is) <br />-Boat is at 4850 rpms wot 28 mph gps with all my fish stuff,tackle and ~ 50L or 12 gal of gas.<br />- I need a new prop, as it came to me banged up<br />??? where do I find specs on props that will fit this motor is there a chart or table on line?<br />??? I guess a 15 pitch would raise rpms, would wot speed decrease?

 

[rickdb1boat]

Re: Used boat new to me with banged up prop

If your Tach. is correct, you are below the optimum wide open throttle RPM's by a bunch. A 15" prop will bring you up about 400 RPM's, but that is still shy of what you need. The speed you gave sounds good and would lead me to believe your Tach may be off. Have you checked the setting on the back of the Tach? It should be set on "6". Any other setting will throw your readings off quite a bit. With that said, you would probably benefit from going to a 15" pitch, as it will raise RPM's and may help with speed too. Certainly on the lower end anyway. If the Tach. is correct and the motor is running good, a drop to a 13" pitch may be in order to get the revs up to where they should be. Check the setting and let us know what you find.. There are others here who know far more than I when it comes to props. So keep looking and one will show up soon...Meantime, here's a link to Michigan props and their prop selector...<br /><br />miwheel.com/MIWheel/html/products/outboard/PSearch.asp

 

[DrinkingEmu]

Re: Used boat new to me with banged up prop

I will check tach tonight<br />-rechecked speed with boat following beside 26.5 - 27.5 (GPS)<br />-The recommended rpm range is 4500-5500. How cautious should I be about the upper RPM# ? <br />-I thought that at about 4900 I was right in the middle of the range ? <br />-15P would maybe make me be at 5300rpms using your + 400<br />-would 5300 rpms still be below optimum ?

 

[rickdb1boat]

Re: Used boat new to me with banged up prop

You always want to prop toward the high end of the recommended RPM range. This will avoid lugging the engine and prolong it's life span. 5300 would be a good RPM to shoot for...

 

[Dhadley]

Re: Used boat new to me with banged up prop

For the best performance and longest life that motor needs to be set up at 6000. If the tach is correct, try to adjust your set up to gain rpm. You may need a different one eventually but try to max out the set up with what you have first.

 

[DrinkingEmu]

Re: Used boat new to me with banged up prop

- Hi, I could not find an adjustment on the back of my tach to confirm if it is at "6". The tach came with the boat from tracker in 92 and looks to just have a number of wires connected to terminals, and a removable light bulb on the back ?<br />- Dhadley, why would Johnson say 4500-5500, but you say "needs to be set up at 6000"? I do not understand this. could you explain, or point me in the direction of info please ?<br />- I will try to get more rpms by adjusting motor on the weekend, as you suggested.

 

[walleyehed]

Re: Used boat new to me with banged up prop

Dhadley <br />Supreme Mariner <br />Member # 685 <br /><br /> posted May 30, 2006 08:08 AM <br />--------------------------------------------------------------------------------<br />At 5500 and below the combustion temps are pretty high and the motor labors or lugs even at reduced throttle settings. If that motor is set up to be able to reach 5800 the combustion temps come down. <br /><br />High combustion temps promote coking which is that black, sticky carbon-like stuff. When the piston cokes up, the rings stick on the backside away from the ring gap. As more and more of the ring sticks in the groove the piston looses support and eventually rocks far enough that it catches the ring and shears it off.<br /> <br />

Dhadley can confirm other stats too, but this is from another post....It has alot to do with the fuel we had when the engine was designed, compared to the fuel we have today (junk)...

 

[DrinkingEmu]

Re: Used boat new to me with banged up prop

Wow !!! Thanks for reply. I was worriedabout over reving the motor. I guess 2 stroke outboards are not the same as my first little 4 cylinder car that I blew up at approx 6500 rpms a few years ago. (valve lifter rod bent, piston snaped off valve '79 austin mini)

 

[DrinkingEmu]

Re: Used boat new to me with banged up prop

OK, last night took out boat after some mods.<br />moved motor up 1 hole, and added some stuff:<br /><br />87 octane 2/3 full tank<br /><br />Prop 17P aluminum Michigan(banged up came with boat)<br />GPS 29.1 with wind <br />GPS 27.9 into wind<br />RPM 5400 (better than the 4900 before)<br />40 hp '92 johnson on tracker tx17 (mod v)<br />6 inch cmc tnt aluminum plate pt130<br />plastic trim wings (proper term ???)<br />slight porpise so had to trim down, boat felt like it rode much higher <br /><br />Prop 15P aluminum Johnson (borrowed to try)<br />GPS 27.2 with wind<br />GPS 26.5 into wind<br />RPM 5800<br />40 hp '92 johnson on tracker tx17 (mod v)<br />6 inch cmc tnt aluminum plate pt130<br />plastic trim wings<br />better hole, but that last 2 mph felt like a loss of 10mph. <br /><br />I think I will get a new 17p and try for 30mph

 

[walleyehed]

Re: Used boat new to me with banged up prop

why not try raising the engine 1 more hole first and see what ya get....this is the fun part!

 

[DrinkingEmu]

Re: Used boat new to me with banged up prop

I do not have a water pressure gauge. The cavity plate is now just above the bottom of the hull. (~1/16th) There is 1 hole left to go, but it would raise it ~ 1 inch. How will I know how high is too high ?

 

[walleyehed]

Re: Used boat new to me with banged up prop

If the AV plate is "just" above the bottom of hull, you won't lose any water pressure. It would have to be 2-1/2 to 3" above to cause a potential problem, I think.