The Original Grok Harmonizer Vacuum Tool


Originally invented by Grok (aka Mark Von Striver) on ADVrider. KATDASH purchased the design and rights from Grok’s family after he passed away suddenly in 2016.

This 2 port vacuum tool has a built-in tachometer that displays with both Balance mode and Gauge mode for accurate tuning and synchronizing of both carbs & throttle bodies. We are doing a final run of 300 of the original Harmonizers. Unfortunately the vacuum sensor in the design is NLA and the pcb has to be re-designed for a new sensor. These final units of the original design are available here – while they last.

The original thread for Grok’s Harmonizer is here:    Harmonizer thread on ADVrider     and you can read reviews and discussions of the tool. The Harmonizer gained in reputation and popularity with both home and professional mechanics. After his death, the final few Harmonizers available were going for $350 and up at auction. One sold for $500.

Please see the bottom of this page for some use instructions and video links.



There are no more Harmonizers available.

Thanks you for your support. If you were able to get one, congratulations! If you missed them, sorry- there just weren’t enough original circuit boards left.

I am leaving this page active for information on the original Harmonizer.

We do hope to re-design and build some more in the future. Paul is hunting for a replacement for the vacuum sensor. However- they likely will not be available until 2023. I will update progress here and on our FB page.



The Harmonizer is a small, portable, battery-powered, Vacuum Multi-Tool intended to aid power-sports engine tuning and diagnostics. It works for both carbureted and fuel injected motors. In addition to vacuum and RPM measurements in both differential manometer (balancer) mode and single –port gauge modes, a few utility/camping/touring features have been included.


Vacuum Measurement and Tachometer Functions:

The Harmonizer has two vacuum measurement modes that both include tachometer functions. Balancer mode and Gauge mode. In both modes, the Harmonizer measures the timing of the vacuum pulses to calculate and display RPM.

Balancer mode displays the difference in vacuum at the two ports. There is a center-zero representation similar to an analog meter, and a numeric representation in the range of ±999 mbar. A smiley face appears if the vacuum difference is 0± 25 mbar. The “needle” sensitivity auto-ranges. If you exceed the limits of the display, the sensitivity of the “needle” is cut in half. The numeric display always resolves to 1 mbar. In Balancer mode the tachometer is calibrated for 4-stroke motors with one cylinder per intake. In Balancer mode, for 2-strokes or motors with 2 cylinders per intake, you must divide the tachometer reading in half.

Gauge mode is a digitally damped vacuum gauge, intended to measure vacuum on intakes that support one or two cylinders. Only one Harmonizer port is used. The other is left unconnected. A left-zero meter representation is displayed along with a numeric representation in the range of 0.00-29.00 in Hg. Gauge mode can be used to adjust idle speed with the tachometer function and mixture (carburetor) with the tachometer and/or gauge function. Gauge mode can also be a powerful diagnostic tool.

In Gauge mode, if you use the yellow port, the tachometer is calibrated for 4-stroke motors, 1 cylinder per intake. In Gauge mode, if you use the red port, the tachometer is calibrated for 4-stroke motors, 2 cylinders per intake (or two-stroke motors, 1 cylinder per intake).


  • Two calibrated vacuum measurement modes with tachometer functions.
  • Reliable, all electronic design, with digital signal processing and no moving parts.
  • Large, easy to read LCD display. No bouncing needle or parallax errors.
  • Auto Range
  • Auto Zero on power-up.
  • Automatic display backlight.
  • Rugged housing with a clear Lexan top.
  • Vacuum hoses are removable. They attach to the unit with a finger tight, twist on Luer connector.
  • Swivel-hook on top for hanging/ attachement. Will operate in any orientation.
  • Auto shutoff after 5 minutes of inactivity (except beacon & timed latern modes)
  • Internal voltage regulation and Battery Voltage indicator.
  • Bright white LED included for convenience & utility.
  • Input button is recessed to prevent inadvertent activation and breakage.

LED modes:
Toggle LED on/off through menu or by a double press of the button for a quick flashlight function.
Timed Lantern Mode illuminates the LED for 15 minutes then power off. During timed lantern mode a single button press resets the timer to 15 minutes.
Beacon Mode flashes the LED in a randomly selected, 5-flash, repeating sequence. Potentially useful as an emergency flasher or locating beacon. Beacon mode does not time-out. It will persist until the mode is changed or the battery is dead.

Storage temperature:  -20C to 70C
Operating temperature:  -10C to 50C

Vacuum Hose size/length/temp:  4mm (5/32) ID x 122cm (48 inches) SAE J1037 -40C to 125C (-40F to 257F)
Battery:  9V Alkaline battery (included) recommended

Displayed Range and (Resolution)-

Balancer Vacuum:  ±/-999mbar (1 Mbar)
Gauge Vacuum:      0.00inHg – 29.00inHg  (0.01inHg)
Tachometer:            0-9990 RPM (<1500RPM  10 RPM steps, .1500RPM  50RPM steps)

Tachometer and internal timing accuracy:  ±0.5% @ 23C (±2% over full operating temperature)
RoHS compliant, CE compliant

* * * * * * 

Here’s a link to a YouTube video of Grok himself balancing the idle on a R1100GS:
Harmonizer R1100GS idle balance
Yes, it’s just that easy. Grok aka Mark Von Striver was a genius!

Here’s a link to a YouTube video tuning the throttle bodies on a Super Tenere: Throttle body sync w/ Harmonizer
This video is by Fred Ziglar and is linked with permission.

Here’s the original Harmonizer Guide & spec sheet:  HARMONIZER_guide_V1_0

Here’s my directions on tuning a Bing CV carb set: Harmonizer Bing_CV