installing a tach on a 77 70hp johnson

[txbandit44]

OK I set this all up and got all the wires connected correctly and found that the rectifier was bad. I got that replaced and now the tach needle moves
So excited it was working.

It was set on 3p and it was shoing that I was idleing at 2500 to 3000 rpm. I figured i needed to move it to 6p and it now reads 1300 to 1500. HOW do you know if this is accurate or not? This thing has a calibration set screw but what the heck do you calibrate too. This is suposed to tell me what the engine is doing. Not me tell it.


Any help is appreciated.


Also I guess this runs off of the charging system. How many poles does the 3 cyl stator have. That may be part of my problem.

 

[Will Bark]

Re: installing a tach on a 77 70hp johnson

Try the 6 P(pulse) and see what happens

 

[Joe Reeves]

Re: installing a tach on a 77 70hp johnson

The alternator of your engine is the component that emits six pulses. This is what your tachomer requires to function properly. Set the dial on that tachometer to number six (6).

Now, on a flushette, adjust the throttle cable at the engine so that the engine idles at 1000 rpm. In the water, the idle rpm will drop to its normal rpm.

 

[txbandit44]

Re: installing a tach on a 77 70hp johnson

Thanks.
Its on 6p now. I will adjust the rpm to 1000 on the flushette and go from there. The only 2 reasons I was adding the tach was to trouble shoot a hesitation at half throtle on the water and to get the right prop on it. As soon as I know I got a true reading I can get started.

Any body out there know if a good hand held lazer tach or rotation meter?

 

[Joe Reeves]

Re: installing a tach on a 77 70hp johnson

Hesitation when applying throttle is usually caused by a restricted high speed jet, a sticking timer base, or having the throttle butterflies opening too soon.

 

[txbandit44]

Re: installing a tach on a 77 70hp johnson

I did a complete rebuild on the carbs. Pulled all the plugs and butterflys out. The top float chamber had the HS jet stuck in it. But it was blown clear. I checked ith with a feeler gauge that matched the other 2 HS jets. I have re-sync'd the throttle linkage and followed the throttle / timming advance instructions i the original manual to the letter. I had not thought of the timmer base sticking. I had checked for binding, but not while the throttle was being advanced.

Maybe that will be the problem. She runs great. The only issues i have now are the hesitation as you roll on the throttlefrom idle to WOT. If I go from idle to 1/2 throttle it doesnt seem to have an issue and 1/2 to WOT no problem. Just idle to WOT right when you hit 1/2 it hesitates and then its fine. It doen not hesitate like you hit the choke. Idle is to high in the water as well. Just another reason for me to get a tach so I could set it right and see what RPM it hesitates at. Also if its the same each time or random.

Thanks Joe I will look at the timmer base for sure.