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I'm going to be doing a carb rebuild this weekend on an 84 Ranger. The truck doesn't have a tach, but I'll be needing to read the RPMs to properly adjust the carb once its rebuilt. Is there a way of getting this information without having to install a tach? There is no obd/obd2 port either.

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up vote 9 down vote accepted

You have a few options out there. There are meters that clip onto the ignition system that show the engine RPMs that are quite simple and cheap:

enter image description here

Tach meter at Amazon for example...

You can also pick up a "timing light" that has a tachometer function. Either of these tools have other purposes for a shade tree mechanic, so find one that you think you will use the most.

Yet another option is a digital, optical tachometer.

They use a laser to bounce off of a reflective object (like the blade of a fan) to measure RPMs.

enter image description here

All products and images for illustrative purposes only. I've never used those in particular.

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In addition to what JPhi1618 said...

You can set any standard tach up with clips. I did this with a cheap tach when tuning my truck.

They have 4 wires - positive, ground, signal, light.
Positive and light go to the positive side of the battery with a fuse.
Ground goes to the negative side of the battery or an unpainted part of the engine/body.
Signal goes to the coil.
Can't remember off the top of my head which side of the coil the signal goes to. I think its the positive side. The tach will work when you connect it to the correct side. You will not damage it by connecting it to the wrong side.

You can also use a dwell/tach meter. These are useful because they typically work in a range of 0-1000, so you can more accurately see the RPM you are trying to achieve. A dwell/tach is best if you have points and need to set the dwell also.

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