BigBadRed

Thanks again, got the 6.5 removed and put in a 4.5. As long as I was there I went to put in a chrome duel feed fuel line. Well, 45 minutes later and still leaking, I took it off and put the rubber hoses back on. It must be defective.

I did remove the carb to do the change, but now I know it was not necessary. I go to start up the car. Does not want to start, keep getting intake backfires. Open up the idel circuits all the way, still getting intake backfires. Look around. DOH!! Carbs work better when the vacum circuits are pluged back in :bb Fires right up but has a funky idle. I swear it sounded like a harley at idle, (maybe 500 rpm) but didn't die. It was almost kinda funny. However it was only pulling 5-6 inches of vacum. Then I remember I retarded the ignition timing in a quest to pass smog. Put the timing back to normal and the engine idled strong around 800 rpm and was now pulling 9-10 inches of vacum. At least a solid inch over what I had before. Plus I got the idle circuit in a full half turn further then I could before, and I still may be able to lean it out even more.

So for you experts, why did changing the power valve definately affect the engine at idle. And specifically why could I go so much leaner with the idle circuit where before it would kill the motor.

Heres my theory, do to the low vacum the engine generated at idle, the old power valve opened at least a little bit. this caused air flow through the wrong circuits. Because the engine was at such low idle, the air flow was to slow to make those circuits work. So I had to richen up the idle circuit to make up for the extra needed gas. However, this basically caused the idle circuit to incorrectly atomize the fuel since it was dumping in way more fuel then it needed.

Am I close???


[Modified by BigBadOrange, 4:43 PM 9/5/2003]

cardo0

Sounds like your proving the theory into practice for us Big Bad. I’m on the learning curve here too (swapping to a spread-bore Holley). And that lower value PV is doing it’s job. Read their designed to open on low vacuum, which is a result of hi, load/open throttle. With the old PV the vacuum never was enough to close the PV – kept feeding too much fuel/too rich.
Expect the venturie boosters dump this fuel and idle circuit is probably fine but competing now with the mains to add fuel.
:yesnod:

Chuck Harmon

The number of the power valve equals the amount of vacuum needed to keep it closed. Power valves are like a second set of jets. When you bury your foot into the carpet, jet sizes that are just right for cruise are no longer capable of giving enough fuel at wide open throttle. Sooo when all the butterfly valves are virtually wide open, your manifold vacuum is at its lowest (unless you have an undersized carburetor). This low vacuum is not enough to keep the power valve shut allowing an extra set of flood gates to open giving more fuel.

Guys that take out their power valves have to run extra rich jets to provide enough fuel at WOT. In your case, because the power valve was the same rating as you idle vacuum, the idle circuit was being helped out by the power valve opening up which dumped in more fuel than you needed or wanted.

When you really begin to understand what the Holley carb can do you realize what an amazing piece of engineering it is. It is then also easier to see how so many guys get into trouble and simply blame the carb. If set up correctly, the carb will transition from one stage to the next without a burble, making smooth and efficient power throughout the whole range.

Chuck

Jvette73

Ive always loved holley carbs. Easy to work on and tune. They have served me well over the years with minimal problems.

Eddie 70

I don't know didly about carbs. My Holley has a stumble in it I can't get right. Just as you touch the gas, small stumble, then go.

Jvette73

Eddie, mine did that too. It turned out that the vacuum advance was the culprit. I switched to ported vacuum and increased the amount of vacuum advance and the stumble was solved. Before you dig into the carb check everything else. :thumbs: