tacho accuracy

[old cruiser]

Just fit an after market tacho , typical style power from ignition ,earth to ground and feed from -side of coil. Problem its reading inacurrate out by 600 rpm at idle then at about 2500rpm it reads around 4000. This is where it gets confusing when I hook up a tacho/dwell meter at the same time as after market one the after market one reads more accurratly? Any ideas whats going on?
thanks in advance

[blackedoutharley]

I know this may sound elementary but did you read the instructions (I never do )?

Some (most) tachs are designed to operate with 4/6/8 cylinders and ignition "pulse" to the tach may be different for each type of engine and can affect the way it displays rpm.

Knowing more about what engine, ignition set up and brand/model of tach might help getting the answers faster.

[lakeroadster]

I don't know if this is what you are experiencing but I will throw it out here.....

I installed an Autometer tachometer in my 1969 Camaro about 3 years ago. The Camaro has the stock factory distributor (points and condensor style). The tachometer readings were erratic and spiked frequently. I called the Auto Meter Service phone number and one of their technicians instructed me to install a 10K ½ watt resistor in the green wire going to the coil. I purchased a resistor and put it on the tachometer wire going to the coil. This helped to keep the tachometer reading from spiking.

[old cruiser]

Its 64 chev c10 , 230 6cyl ,points style dissy. Tacho switch is on 6 cyl.

Lakeroadster may be on the right track as dwell/tacho when hooked up aswell might be creating enough resistance for other tacho ?
Sunday today can,t do much until during the week. Any other ideas are welcome also

[old cruiser]

Finally got around to toy with the pickup today. Wired in a resistor between coil and tacho thanks lakeroadster for the idea . I took resistor out of a damaged amplifier its adjustable and just dialled it in till tacho was as close to accurate as I could get and according to my tuning tach its pretty damn close. Thanks for input guys

[63 & 64 Bowties]

I'm glad we got that figured out because I was getting really hungry for some Mexican food.

[lakeroadster]

Originally Posted by old cruiser

Finally got around to toy with the pickup today. Wired in a resistor between coil and tacho thanks lakeroadster for the idea . I took resistor out of a damaged amplifier its adjustable and just dialled it in till tacho was as close to accurate as I could get and according to my tuning tach its pretty damn close. Thanks for input guys

Glad I could help.... Now tach that thing up

[lakeroadster]

Originally Posted by old cruiser

Its 64 chev c10 , 230 6cyl ,points style dissy. Tacho switch is on 6 cyl.

Lakeroadster may be on the right track as dwell/tacho when hooked up aswell might be creating enough resistance for other tacho ?
Sunday today can,t do much until during the week. Any other ideas are welcome also

......

[old cruiser]

Thanks again guys.
63 & 64 bowties hope you enjoyed your mexican food I prefer doritos to tacos but not too spicey
Just to recap tacho was switched to 6 cyl setting but still needed a resistor as advised by Lakeroadster good call thanks

[Vernski]

Originally Posted by blackedoutharley

I know this may sound elementary but did you read the instructions (I never do )?

Some (most) tachs are designed to operate with 4/6/8 cylinders and ignition "pulse" to the tach may be different for each type of engine and can affect the way it displays rpm.

Knowing more about what engine, ignition set up and brand/model of tach might help getting the answers faster.

Blackedoutharley is right about the newer tach's they are for 4-6-8 cyl and if you read the instructions they will tell you about the little switch on the back of the tach and you can switch it from 4-6-8 cyl. When all else fails read the instructions....Vernski