Found an economizer valve cover to accommodate the two-stage valve, but it has a vacuum port on it. I assume since my current cover does not that the PV gets is source internally.

So I can just plug this port off now?

 

Yes, you can plug the port on the cover. Yours gets its vacuum via an internal passage in the carb.

 

I just did some more reading on the two-stage economizer valve.

Some suggest that the two-stage economizer valve was used in conjunction with the EGR emission system. The first stage is designed to open sooner to try to get rid of a lean part throttle miss. And a carburetor that had the two-stage economizer valve will tend to have smaller main jets than an earlier carburetor with the single-stage economizer valve.

This makes sense, because the EGR system effectively leans the fuel mixture and slows the burn at part throttle when engine is warm. As many others here can attest, an engine will often ping at part throttle when the EGR system is disabled or removed. Later "emissions" engines had a much slower advance curve to work with the EGR system. Re-curving the distributor and/or replacing the carburetor with an aftermarket or non-emissions carburetor is often required when removing the EGR system to eliminate pinging.

So, *maybe* the two-stage economizer valve is beneficial with those engines that still have a functioning EGR system and stock "emissions" advance curve, and an earlier "non-emissions" engine without EGR and a more aggressive advance curve would be better suited with the traditional single-stage economizer valve? Perhaps this is why Holley stopped making the two-stage variety; these engines are old enough now that hardly anyone rebuilds these anymore with the stock emissions equipment anymore to need it?

 

Another aspect is that early on people weren't too worried about MPG, so carbs were jetted rich enough that there wasn't much of a bog when easing into the throttle. And the only enrichment that was needed was near full throttle.

But, when MPG became an issue they leaned the carbs down and there was a real bog, or at least a flat spot in acceleration, when easing into the throttle to pass on the highway. My '72 F250 w/a 390 was jetted so lean that nothing happened until the PV opened. It just essentially didn't accelerate. So, I rejetted richer and fixed the problem. But, a two-stage PV would have solved it and kept the MPG up.

 

So I am ready to throw this carb OUT THE WINDOW!! It's already the wrong carburetor- came off a '77 Bronco (NO, I did not do this- previous owner). Jets are wrong, PV is wrong. So I ordered the right jets, got a kit with the right PV, found a PV cover. JETS AND COVER are WRONG! This has been an uphill battle.

The jets are wrong because the threads are different. I ordered the jets according to the parts list based on the carb number that SHOULD be installed. So my thought is that the threads for the jets were different in 1977 than they are in 1984? Only explanation I can think off.

The threads in the carb are coarse whereas the jets I ordered are fine thread.

As for the PV cover, I think I have the correct one coming but the truck has been in the driveway for 3 weeks. I just want to get it done!

 

Did the jets have an "F" behind the number?

 

Crap, I already know where you're going with this. I assume the "F" indicates fine thread? Yes, they do have an "F" after the number.

 

Just did a little more research. Looks like thread size changed in 1964 to a larger thread. The jets I ordered must be for 1963 and earlier. Part number prefix is C3DZ- which if memory serves, puts that part number right at 1963.

 

Pre-64 Ford jets are the same size as Holley.

 

I've never known what the F is for, but maybe it is for "fine" or "Ford". I wasn't aware that the jets changed. Learn something every day.

 

I can't seem to find what size thread the new ones (post-1963) are, but the old ones are 5/16x32. Anyways, I think I found the correct ones, I'll know by Saturday. A carburetor site pointed out that they are different after '63, I just missed it in my haste to get the parts together.

 

This site (Archive: CARB - JET CHANGE - The DIRT Forum) says that Holley jets are 1/4-32 and Motorcraft jets are 5/16-28. They even tell how to convert from the Motorcraft to Holley jets by tapping a Motorcraft jet to take the Holley.

 

Maybe I had my TPI wrong. So pre-1964 jets fit Holley as well (as Tedster pointed out) with 1/4" threads while everything after uses the larger thread of 5/16".

I actually thought about tapping out the holes but I don't want to go through the nonsense and screw something up. I looked for decent carb cores before I started but there doesn't seem to be too much out there.

 

To further confuse things Holley jet size diverges from the numbered drill size, at least for the jets above #50, although I believe the Holley are identical to the Ford jets number for number up to that point so it shouldn't matter too much for stock carbs. Seems to be close anyway. Holley made the carbs back then afaik after all.

 

Holley's jets are rated on flow rather than drill size. They do that to some extent by the entry and exit angles, and in many cases three different jets have the same hole size. Here's info from Dave Emanuel's book on Holley carbs:

• Jets no. 80, 81, and 82 all show a number .093 drill size.
• Jets no. 88, 89, and 90 show a .104 drill size.