Ok guys, bear with me here. Just ripping my Holley 4175 apart for the fun of it...
See http://forums.corvetteforum.com/show....php?t=1727007

OK, so I download the exploded view diagram of the 4165/4175 from the Holley site and it shows 2 metering blocks, a primary and a secondary.

I dont have a secondary metering block..Im like wtf. Now I am new to carbs so excuse my ignorance.

Am I supposed to have 2 metering blocks with this carb? The list # is 7002-1 Is this a 4175? lol...

 

s'ok found some pics of this carb installed on other cars...same as mine. Must have the wrong exploded!

 

You can find tuning plates here.

http://www.holley.com/types/Metering%20Plates.asp

BigBlockk

Later.....

 

Thanks for that. OK so this is where I fall flat on my face. For the Qjet I simply asked Lars..he told me what jets and rods etc etc.

How do I tune this Holley for my car?

It has 63 jets at the mo and my specs are 350 +.030, Comp Cams Part # 12-210-2, Grind number : CS 268H-10, 2 1/2" Dual Chambered exhaust, Auto trans with sat night 2000 stall, 3.08 rear rest is stock.

TIA.

 

Make a list of what you have now. This would be jet sizes, air bleed sizes, power valve numbers and the specs on the metering plate. Also record the adjustments as the carburetor sits now. This would be idle mixture adjustment, transition slot, float level and accelerator pump.

Then you need to ask yourself how the car performs now. Does it idle OK and how is the tip in. A lot of Holley's idle rich. This is mainly to cover up for lean tip in as you open the throttle (slightly) coming away from a stop light. You can do the wire trick on the idle channel restriction to clean up the idle.

How does the cruise feel? I'm talking about 60 MPH here. Does the engine surge under cruise conditions? Surging is a lean condition. Fattening up the idle mixture can help out a little but it isn't really the right way to go about it. This type of operation is mostly main jets and main well air bleeds. This is an emissions compliant style carburetor (in that it is designed to replace the Quadrajet) so everything above idle is probably going to be lean. This can give the feeling that the accelerator pedal is not hooked to anything in certain areas of the throttle travel. These are lean sags. Richening up these areas will improve throttle response. I would get the next 4 jet sizes up from what you have now for the primary side. Take vacuum readings to make sure the power valve is not opening up at cruise.

Right about now you need to disconnect the secondaries.

Now we can get into the primary power circuit. This is where the power valve comes into play. There are two components to the power valve system. The first is the valve itself, it must open when the engine is under load and needing more fuel but not be open at high cruise. The valve controls WHEN the power system functions. The second part of the power system is the power valve channel restriction. The PVCR controls the AMOUNT of fuel the power system flows. A lot of guys make the mistake of think that changing the power valve will lean or richen the power system. This is not the case. If you have the power system timing right but the PVCR is too small you will feel a sag on hard acceleration. The car may come off the line great but it will lay down at about 3500 RPM.

If you don't have a chassis dyno you will need to make timed runs to gauge your progress. Find a level section of road where you can kick the transmission into passing gear at about 35 MPH. Time the car with a stopwatch between 40 and 70 MPH at WOT. Make ONE change at a time and retest. If the car gets quicker you know you're going in the right direction. You are using the weight of your car as an inertia dyno.

The trick is to get all these systems to transfer from one to the other seamlessly. The progression is, idle, transition circuit, main jet and then power system. The accelerator pump system attempts to cover the holes between them all.

Get yourself a good carburetor book, some jets and a couple power valves and have at it.

http://www.jegs.com/webapp/wcs/store...10002_36856_-1

When you get this all done we can start on the secondaries.

BigBlockk

Later.....

 

The Holley book I had as a kid made me totally dangerous when tuning carbs. BigBlockk's advice is right on. Read the book! Holley makes tons of parts to tune their carbs. Holley used to make a "track pak" that had a lot of tune-up parts in it.
Down the road you can convert that carb to a metering block if I remember right.

JS

 

Holley has a free downloadable manual and troubleshooters guide.
Its close the book.
http://holley.com/TechService/Library.asp

 

new pump, pv
good idea
if it works fine, don't fix it.
(bigger jets will kill mpg)