Untitled Document

Vacuum Secondary Performance

MIG Gas Delivery and the Small Block Chevy Evolved in a Similar Way and Time!

Both had Advances and Setbacks Before

They Were Optimized!

Click for a PDF Report on the Similarities

See Video " Tuning Holley Carb"

See YouTube Video Discussion of Our

Patented Shielding

Gas Saver System

CLICK HERE OR PIC OF OUR STREET ROD

The Vacuum Secondary Holley 850 CFM Carb that came with the ZZ502 Chevy engine was model number 0-80531. It came with #78 Primary Jets, a 30CC accelerator pump with 0.035 Squirters, a 6.5 Power Valve with Power Valve Fuel Passages of.0.045 inch diameter. The Secondary came with #82 Jets, a 6.5 Power Valve with 0.049 inch diameter Power Valve fuel passages and a Pink spring on the secondary opening diaphragm.

Out of the box the car was obviously running rich at idle and when cruising. It also had a Bog when trying to accelerate. It was fowling plugs so the Primary Jets were decreased to #76. Plug fowling was eliminated but there was the same slight Bog when the accelerator was rapidly depressed. It appeared the mixture needed to be richened and the following table presents the various modifications tried over a 6 month period:

Test #	Spring Color	Needle Valve Setting, Turns Out *	Changes Made	Comment When Accelerating	Air/Fuel Meter Reading when Aceller.
1	Pink	na*	#76 Pr. Jet;4.5 Pr. PV	Bog	na**
2	Pink	na*	.045 Squirters; 50cc Pump	Bog	na**
3	Pink	na*	.057 Pr. PV Fuel Passage	Bog	na**
4	Plain	na*	.067 Pr. PV Fuel Passage	Less Bog but slight Hesitation	na**
5	Pink	na*	#84 Sec. Jets: and 3.5 PV	Slight Bog	na**
6	Pink	na*	.070 Pr. PV Fuel Passage	Slight Bog	na**
7	Pink	na*	J Extensions Added to Sec.	Very slight Bog	na**
8	White	1 1/2		Very slight Bog	na**
9	Pink	1 1/2		Slight Bog improvement but slight Hesitation	na**
10	Purple	1 1/2		Slight Bog improvement but slight Hesitation	na**
11	Purple	1		Bog almost gone	na**
12	Purple	5/8		Bog almost gone	na**
13	Grey	5/8		Slight Hesitation	Very Lean
14	Grey	5/8	.052 Squirters	Slight Hesitation	Very Lean
15	Grey	1	.o45 Squirters	Slight Hesitation	Very Lean
16	Grey	1	Rubber Band on Sec. to hold it shut	No Bog but sluggish response	Very Lean
17	Plain	1	.031 Squirters	No Bog but sluggish response	Very Lean
18	Pink	1		Slight Hesitation	Very Lean

*Adjustable Needle Valve Diaphragm not purchased until 2nd half of tests

** Air/Fuel meter was not installed until near the end of the Vacuum Secondary carb tests

The above tests were made with the various Secondary Diaphragm springs and the Special Adjustable Secondary diaphragm purchased. The special diaphragm housing incorporates a needle valve so the rate of vacuum applied to the diaphragm can be controlled. It was not significantly better than using a stiffer spring which can eliminate the Bog (a drop in RPM upon opening the secondary quickly) but created a Hesitation (the Secondaires open so slowly you don't get a Bog but you can feel the slow opening). The springs were ranked as to stiffness by using a postage scale and measuring the force at two points. The following table shows the force when fully opened and when the secondary butterflies are closed:
Spring Color	Force in oz when throttle open	Force in oz when throttle closed
Black	20	8
Brown	17	11
Plain	13	7
Pink	9	6
Purple	8	4
Yellow, Long	7.5	4
Yellow, Short	7	3
Grey *	6	2
White	5	2

* Came with the Adjustable Secondary Diaphragm

▲Return to Modifying Holley Home Page

▲ Go to Double Pumper, It Solved the Problems !!

Engineering a 1934 Pro Street Street Rod

Click for a 67 Page PDF

Click for YouTube Video Overview of Car

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"WARNING: "Weld Safely"
Details of the 1934 Pro Street Rod

The "Flow Rate Limiter" device is covered by 2008 US patent # 7,462,709. Other site material may be covered under Patents # 7,015,412; # 7,019,248 or # 8,104,094

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