Tach adjustment help?

[100333624]

Hello!

So I finally got my tach running after realizing that the brown wire from the tach doesn't go to the rectifier, it goes to the brown terminal on the switchbox! After hours of fighting with it, reading online for help and adjusting the tach, BOOM it worked! So now that I know the tach works, how do I know that its set properly? I have it set at the "4" dial on the back for the 12 pole setting. The motor its running off is a 1978 mercury 800 4 cylinder with CDI coil per cylinder, and the tachometer is an older used quicksilver one with the black background and white/orange letters, I had to test to see if it worked.

How do I adjust it to know what rpm its on because right now its reading at 500 rpm at idle which is too low I think? It seems like the motor is idling at around 800-1000 rpm from how fast it sounds, if I move the dial just a tad off of "4" it reads at 1000 rpm which seems more realistic I think. I can adjust the idle lever a bit by hand and it idles around 200-300 rpm less. What is my motor supposed to idle at normally? How do I know my motor is idling at the proper RPM or how do I know the tach is reading the proper rpm? Any advice?

Thanks!

Nick

 

[Barnacle_Bill]

Re: Tach adjustment help?

There is a brown wire on the switch box but that is not the tach lead. It goes to the trigger. The tach's brown wire ties in to one of the yellow/red wires coming from the stator. This connection is made at the rectifier. Idle speed should be 550-650 in fwd gear.

 

[100333624]

Re: Tach adjustment help?

There is a brown wire on the switch box but that is not the tach lead. It goes to the trigger. The tach's brown wire ties in to one of the yellow/red wires coming from the stator. This connection is made at the rectifier. Idle speed should be 550-650 in fwd gear.

Yes but when I put the brown wire from the tach onto the rectifier it doesnt read anything... doesnt work. Could it be I got a bad rectifier?

 

[Chris1956]

Re: Tach adjustment help?

The old Mercury tachs ran off the switchbox. The newer tachs run off the stator. I never had an old tach, but you can try different settings. It is doubtful your motor is idling at 500 RPM. 800-950 is much more likely.

 

[100333624]

Re: Tach adjustment help?

I tried 3 different tachs today all on rectifier and on the switch box, only switchbox worked with all but one didnt work at all.. Seems like it read the rpm ok at times and sometimes not ok... like when I dropped the idle a lot it dropped rpm to 100-200 which is impossible, but as soon as I raised the throttle it went up to 1000 which sounded like it was around there.

The other tach was jumping all over the place and it would give me different readings if I held it up or laid it down... weird... Dont know if I can trust this one now or do I cough out $70 for a new one..