Sunday, January 6, 2019

Quadrajet Tuning: How to Connect a Handheld Tachometer

If you plan to fine-tune your Corvette's Quadrajet carburetor, one tool you may want to have handy is a handheld tachometer. This allows you to check and adjust the vehicle's idle speed while you wrench under the hood.

If you have a timing light with RPM-reading capabilities, you can use one of those, but this article is for those of us who have or prefer a handheld tachometer.

I found a used vintage RAC Maxi-Tune on eBay for about $20. Needless to say, you take your chances when buying anything used, especially electronic equipment manufactured in the 1970s, but luckily for me, the one I bought works fine.

The RAC Maxi-Tune is a multi-function ignition analyzer. It can measure low (idle) and high RPM, dwell, dwell variation, point condition, idle mixture, power balance, and more. But for this article, I'll focus on the RPM function exclusively.

Since my car has electronic ignition, I had to devise a way to connect the analyzer so it would read the engine's RPM and the easiest option was to use a solid 14-gauge copper wire to do so.


I used the wire shown above to tap into the tachometer plug so I would have a live terminal for the analyzer's test clip to connect to.

The picture on the left shows the location of the tachometer plug. Brown plug and wire.

The purpose of using the solid copper wire is so I would have a temporary live connection for the Maxi-Tune analyzer. I am sure you can fashion a similar connector but please don't pull a Bubba by stripping the wire. That's unacceptable.

Also, I used an insulated wire since I wanted to avoid accidental arcing since the motor must be running for the multimeter to work.

The Maxi-Tune ignition analyzer came with a helpful instruction booklet, so if you buy a used one, make sure it includes the manual.


I disconnected the tach plug since this makes it easier to insert the external wire. This is especially important if you are using stranded wire.


I inserted the wire at the connector's base and verified it made proper contact with the metal tab inside the plug.

The photo on the right shows the tachometer connector plugged back in on the side of the distributor while the arrow points to the external wire.

At this point, you are ready to connect the multimeter to monitor engine RPM, but first, you have to connect the Maxi-Tune analyzer to a power source, which in the case of a C3 Corvette is the battery located behind the driver's seat.

Even though the Maxi-Tune has long battery wires, they were barely long enough for my C3 Stingray, so I added a couple of feet of wire in order to be able to work comfortably under the hood.


The photo above shows the Maxi-Tune's tachometer/dwell/points test clip hooked up to the RPM feed via the external wire.

The multimeter "Number of Cylinders" switch must be set to the 8 cylinder setting and the "function" switch to either Low or High RPM. If you are fine-tuning the carburetor, for example, you have to use the Low RPM setting.

In this short video I shot, you can see the Maxi-Tune Ignition Analyzer in action.


Even though this info may be very basic or old news for those of you who know how to use automotive multimeters, I thought it was important to explain, in some detail, how to connect and use them for those C3 Corvette owners who are unfamiliar with multimeters/ignition analyzers but who may be interested in getting and using one.

Earlier C3s have an ignition coil—and a cable-driven tach—so the tach test clip must be connected to the distributor terminal of the coil. But since my '76 came with electronic ignition, I am using that system for this article.

I hope you find this post helpful.

Thanks for following.


More Quadrajet Articles from my Blog

• Getting the Rochester Quadrajet Rebuilt | 2/23/2016
• Remanufactured Rochester Quadrajet Carburetor | 4/1/2016
• Carburetor to Air Cleaner Gasket | 2/2/2018
• Quadrajet Tuning: Adjusting the Idle Mixture Screws | 12/20/2018
• Quadrajet Tuning: Replacing the Idle Mixture Screws 12/26/2018


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