Wrong Tachometer?

[Imtrying]

HI all...I took the 70hp Johnson out for second test run today after I installed a tachometer. Only thing is I think I put a missmatched tach for that motor. Of course the 70 is a 3 cylinder, and on the tach it says on the back: for 4 cylinders...( I put the dial on the back on 6p)does that make a difference? (I probably answered this question) but, the boat I have is a 16' starcraft that is pretty heavy. Boat, motor and trailer weight 1600 lbs. Anyway, it did get up to 35 mph., but the tach only read 3200 rpm. WOT. Does that sound about right for that motor and the tach I put on? I also tried different tilts, first hole, all the way down, 32 mph....third hole, some porpoising, 4th hole, severe porpoising, 2nd hole, perfect plane, and no porpoising, and again 35 mph. According to the manual I should be getting 5000 rpm with the 13 1/2 x 17 pitch on the prop. Should I get a different tach, or does the statments above sound about right? Tia...Dan

 

[OBJ]

Re: Wrong Tachometer?

The 3200rpm don't sound right for your speed. Should be indicating at least around 5krpm. What kind of tach or brand did ya' get? Did you read the instructions all the way through? Some TeleFlex tacks need the installation of a resistor to work correctley.<br /><br />If the second hole gives best performance, leave it there.<br /><br />Keep us posted....always a wrench hangin' out to help you out.

 

[rickdb1boat]

Re: Wrong Tachometer?

A 70 HP Johnson, assuming it's running good, a 16' boat, a 17" prop and 35 MPH = Bad tach... You're running right where you need to be.. If the Tach says "4"-"6" cylinder, it's the wrong Tach.

 

[Trent]

Re: Wrong Tachometer?

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

 

[Imtrying]

Re: Wrong Tachometer?

Thanks guys...The tach is a Faria...and of course it reads "for 4 cylinders engines" (should have paid more attention)on the back...all the readings/settings on the back are for 4,6,8 cylinders...I got it off ebay for $15, so I can resell it and get another one...On another note...Trent..I clicked on your link...but noting happened...blank page....Thanks again, Dan

 

[angus63]

Re: Wrong Tachometer?

Are you sure it says "cyl's". Usually the setting is for "pulses", in which case you should set for 6 pulses per rev. Can't hurt to try.<br />Good Luck

 

[Imtrying]

Re: Wrong Tachometer?

angus63 <br />Captain ..I have it set at 6p, which I presume is 6 pulses...other settings are 4cyl, 2 pulses, 6c, 4 pulses, etc. Like I said, I have it set on 6p, and only reading 3200 rpm at WOT. The motor runs smooth, and "sounds" like it is at full rmp with WOT.....I could try and set it at the other settings while running, do you think that would make a difference on the reading?...Dan Oh, by the way, at idle/low warm up, it reads 900 rpm...

 

[Imtrying]

Re: Wrong Tachometer?

One more thing if you guys are still out there...What IF the tach is working right? How would I get 2000 more rpm's?

 

[rickdb1boat]

Re: Wrong Tachometer?

Imtrying <br /><br />You can't. Unless the engine is really running bad. Is it? I doubt it, since you are getting 35 MPH out of your set-up now. No amount of propping will gain you that much. Even if you went to a 11" pitch, you would still only be running 4400 RPM's. Still way too low. I'm thinking a 15" would be right on the money for your boat. And your boat doesn't really weigh that much. Maybe 800-1000 pounds, with out the trailer and motor. Try a new tach and I think you will be right on the money or real close. Like you said, you can re-sell the old one, so you're really only looking at another $25.00-$30.00 for a NEW one. Is there a outboard shop near you? They may have a test Tach that you could hook up temporarily to verify your actual RPM's. You would want to be super nice to them, explaining your situation and even offer a small deposit. But it would be worth the peace of mind knowing that yours is bad or good.

 

[angus63]

Re: Wrong Tachometer?

If I recall correctly, Faria tachs are used with force and mercury outboards (like those supplied in bayliners). When I repowered, I swapped tachs with a teleflex and all was well.<br />Good Luck

 

[Imtrying]

Re: Wrong Tachometer?

Ordered a new tach...should be less than a week? I'll keep you all informed...Thanks for all the help....Dan

 

[benyshep]

Re: Wrong Tachometer?

These postings have me concerned. I have a 1979 Johnson 70 and have recently purchased a Faria tach. My boat doesn't have one now and I hope to use it to get my prop selection right. Anyway, this one shows it's compatible with 4, 6, and 8 cyclinders and 12-pole alternator outboards. My motor is listed as 12-pole, so this should work, right? Also, I have no gray wire under the dash, and no manual. Should the ground go right the the battery negative and how do the splice or hook into the pulse wire on the motor. Thanks......