tachometer not reading right

marquette

Petty Officer 1st Class
Joined
Apr 18, 2006
Messages
372
i just put a teleflex tach on my boat and it seems to read too high of rpm. i have it on a 1986 johnson 28hp spl. when the motor is at idle it is reading about 1300-1500 rpm and it is easy to hear the motor is not running that fast. at wot it reads almost 6500rpm. it doesn't sound bad at wot and considering it is pushing a 15 ft fiberglass tri hull with a 9 1/4 x 12 prop i don't think it could get to that high of rpm. i have the pole setting at 5. i double checked teleflex's chart and 5 should be the correct setting. does anybody know if johnson used differant pole setting for the 28spl? or even on the 25 or 30 hp? the tach zero's out when the key is turned on so i assume the zero setting is right. i'm using the johnson 3 wire plug wiring harness plugged into the control box for my feed so i also am assuming that it is wired correctly. black-ground purple-ignition grey-send i know i could just assume it is reading 6-800 rpm high and just subtract from the reading but that seems to defeat the purpose of a good tach. anybody have any suggestions of what to try?
 

Randyg123

Petty Officer 1st Class
Joined
Apr 20, 2008
Messages
337
Re: tachometer not reading right

The chart I have says:

Two cylinders less than 70-hp are 10-pole, with the exceptions noted below.

Just about all else are 12-poles including
9.9 HP & 15 HP (2 cylinder, 4 stroke)
25-35 HP 3 CYL
40-50 HP, 2 cylinder (1993 & later)
60 HP, 3 cylinder (1985 & later)
70 HP & greater, including sea drives
All FICHT models

So I guess if your model is a 2-cylinder then five should be correct. Double check and makes sure the dial is set firmly in the '5' position and not kind of half way or sticking.

Can you confirm rpms with another tach?
 

dajohnson53

Lieutenant Commander
Joined
Apr 28, 2004
Messages
1,627
Re: tachometer not reading right

i just put a teleflex tach on my boat and it seems to read too high of rpm. i have it on a 1986 johnson 28hp spl. when the motor is at idle it is reading about 1300-1500 rpm and it is easy to hear the motor is not running that fast. at wot it reads almost 6500rpm. it doesn't sound bad at wot and considering it is pushing a 15 ft fiberglass tri hull with a 9 1/4 x 12 prop i don't think it could get to that high of rpm. i have the pole setting at 5. i double checked teleflex's chart and 5 should be the correct setting. does anybody know if johnson used differant pole setting for the 28spl? or even on the 25 or 30 hp? the tach zero's out when the key is turned on so i assume the zero setting is right. i'm using the johnson 3 wire plug wiring harness plugged into the control box for my feed so i also am assuming that it is wired correctly. black-ground purple-ignition grey-send i know i could just assume it is reading 6-800 rpm high and just subtract from the reading but that seems to defeat the purpose of a good tach. anybody have any suggestions of what to try?

Your teleflex tach should have a chart in the instruction materials that will tell you how to set the tach (little knob on the back) to properly read the pulses from your engine. If you don't have that, check the teleflex website, all their installation materials are on line.
 

marquette

Petty Officer 1st Class
Joined
Apr 18, 2006
Messages
372
Re: tachometer not reading right

i double checked the teleflex web site and they say 5 for the setting. i checked against another tach (which i don't know if it is accurate) and it showed my tach at about 3-400 rpm high at idle. does any body know haw to check the zero on a tach? this one locks at what ever rpm it is when the key is shut off. i think taht this is just a generic teleflex tach. are there differant tach for 2 stroke, 4 stroke, brand ,ect? this was a new boat take off because the owner wanted honda guages for their honda but i just assumed tracker would use a generic gauge because they wouldn't know what motor was going to be mounted on the boat. can i harm the tach or motor trying another pole setting?
 

Randyg123

Petty Officer 1st Class
Joined
Apr 20, 2008
Messages
337
Re: tachometer not reading right

As you said, 5p is correct according to the Teleflex website, "2 cylinder 4-35 hp (1977-91), 2 stroke 5P". Unless...If your engine is a four-stroke, then it should be set to 6p.

I think you are also saying the second tach was reading lower values with your idle around 1100. Is this in gear, out of gear, in water, on muffs? 1100 is not such an unreasonable idle speed on the earmuffs. I don't know what the true idle should be for your motor.

Now you have two tachs giving two different readings and ou don't know if either are correct:eek:
 

marquette

Petty Officer 1st Class
Joined
Apr 18, 2006
Messages
372
Re: tachometer not reading right

i borrowed a digital test tach from a neighbor yesterday. it has the lead that clips around the spark plug wire and had a 9v battery. pretty simple to hook up and use. it was reading at idle in a tank of water in neutral 750rpm which sounded about right. i used the fast idle lever and set it at 1000 rpm and then turned the zero adjustment on the back of the teleflex tach to match the 2 readings. then set the lever back to idle and the 2 tachs still agreed. since the motor sounded like it was running slower than what the telefex tach said (before adjustment) and the digital tach is supposed to be a test tach i just decided i needed to make a decision which tach was right and adjust to it. hopefully i made the right decision.
 
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