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Old 02-06-2009, 02:48 PM   #1
Michael Mayben
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Default The Mityvac Thread

In this discussion, we talked about the use of the mityvac hand vacuum pump around the shop...primarily for one-person brake bleeding operations:

http://www.forums.IHPartsAmerica.com...-bleeders.html

Let's look at some other uses for one of these devices, this version is the "repairable" (I throw 'em away when they are beat beyond use which is about twice a year).

Here's the variation which carries a p/n of mv7000 and marketed as the "brake bleeder" kit. All parts needed to bleed various types of brake or clutch-related hydraulics are included. The myriad hard rubber adapters are indispensable in using this tool in carburetor and ignition work also. The small instruction manual included is very helpful regarding "what" engine-related items can be tested or actuated, though it does contain some technical errors and misspellings.

Street price for this variation of the mityvac system is under $40 currently. This one May also be used to provide a "pressure" source for verifying some actuators and other devices.

Anyone working with the various vacuum systems on this old iron should have a mityvac (or one of it's clones) in the toolbox and carried on the road!

The adapter set ups shown here are what I scabbed up today for testing Holley carb power valves and power valve actuation systems. The "suction cup" adapter is made for testing Holley modular carb power valves and is included in the mv7000 kit.

And the vacuum gauge alone is a newly-designed part that is much higher quality that what has been used in the past, this one is good enough to be used as a stand-alone vacuum gauge for carb tuning...but it will not read pressure so therefore ya can't use it for testing fuel pumps!
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Old 02-06-2009, 02:57 PM   #2
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Default Re: The Mityvac Thread

Here's the pump being used with the suction cup adapter, and placed over the "vacuum side of a Holley modular carb power valve. When pumped, if the valve diaphragm is good, then this will hold vacuum for several hours and keep the enrichment valve closed (duplicating engine running conditions at idle vacuum level.

And if the calibration for a single stage power valve is unknown, this tool can be used very carefully to determine the value/calibration of a power valve...not exact calibration, but real close!
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Old 02-06-2009, 03:00 PM   #3
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Default Re: The Mityvac Thread

In this pic, ya see a Holley "two-stage" modular power valve being tested. For this I added a small length of very soft closed cell neoprene tubing that slides snugly over the vacuum port on that two stage valve.

Again, pump the pump and watch the valve actuate...then pause so any leakdown of the valve assembly is noted while watching the gauge.
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Old 02-06-2009, 03:04 PM   #4
Michael Mayben
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Default Re: The Mityvac Thread

Here I rigged one of the "needle" adapters to insert in the vacuum transfer port on the bowl cover of a Holley "22xx" carb. This is the vacuum source for the power valve actuator piston, that long brass "spool"-appearing item between the two bleed tubes.

As the pump is actuated, that piston should retract but will not hold inna retracted manner...it's not supposed to. The biggest problem we find with these carbs is either a piston that won't move, or one that simply will not hold vacuum. The proper operation of the power valve circuit is imperative to correct performance of these carbs, after rebuilding, this portion of the carb must be tested before re-assembly.
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Old 02-06-2009, 03:09 PM   #5
Michael Mayben
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Default Re: The Mityvac Thread

Here ya see an assortment of typical Holley distributor vacuum canisters.

These items begin to actuate when approximate 5>7"hg are applied to the inlet fitting...then they provide a rotation of the breaker plate of between 5 and 7 degrees of rotation as determined by engineering specs.

None of the vacuum canisters in this pic are any good, all leak and will not actuate at all. All are candidates for being rebuilt, as new canisters are not available except through some vendors who might have nos stuff, or new aftermarket parts still in inventory.
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