I have what i think is a Holley 390 installed on my slant six. Im getting pretty bad MPG and when the secondaries open up it will lean it out too much. So i was curious on how i can tell if it is a 600. I bought it reman from ebay.

On a holley it is easy to determine if the carb (and some parts) are what they are...

Easy Spot:
pull the air cleaner and stamped on the front of the air horn, just above the air cleaner lip are 1 or 2 numbers the one that starts 0-XXXX is the carb number that you will use to look it up in a catalog (for the carb and it's CFM or for a rebuild kit)...yours should be a 0-8007 if it's a 390 cfm vacc. secondary carb...if it's a 450 cfm carb is a 0-1848...if it's a 600 cfm...you get some flavors like 0-1850-(1,2, or 3 depending on choke variation), or 0-80457....etc...

To determine if all the parts match on some modern holleys and some OEM holleys the fuel metering block will be also stamped with the carb number and a batch number (so if you have a 8007...the top of the block will be stamped 8007 and a batch number)...on some OEM holley's the throttle plate assembly can also be stamped with the carb number as well
(so if you find an old Jeep with a 4 barrel holley and it is stamped List-4321- a 390 cfm holley with secondary metering block and a secondary power valve... and the metering block is 1850, and the plates are 1848...the carb is completely mismatched and won't work well at all).....

If you find it is a matched 8007 Holley...I would buy the secondary metering block kit, and remove the secondary plate and install the block with two #52 jets to start with and tune it from there...also, power train components will have an effect on using the 4 barrel effectively...a set of 2.76's in the rear behind a stock 8:1 engine will kill mileage pretty quick...a set of 3.23's and a 9:1 min. compression and RV cam will help keep the 4 barrel happy...PV selection will also play a part in overall mileage especially if you are whacking the secondaries open all the time...


Let us know what you find on your carb,

-D.Idiot

I did check the number on the air horn and it is 8007 so I do have a 390. As for the other numbers I did not because I was in a rush. My setup is about 8.5:1 compression, 2.76 gears, and a comp cam, .440 lift and 264 duration. I was getting about 16 mpg, then I put an ignitor kit in so it was wanting some more fuel so I switched from the #46 jets to #50's. Its got an 8.5 power valve and im debating on putting the 6.5 back in. I ran the #50 and 6.5 PV for 3500 miles and got 16 mpg no matter what. I just recently put a ligher secondary spring in and got them to open up. Everything went downhill from there.

Although the engine is on the light side for that cam (would recommend 9.2:1 SCR...) and the cam likes things in the higher rpm range (2.76 a bit low)...If you are determined to work with the combo as is, I would highly suggest daily driving with a vacuum gauge hooked to the nipple under the primary fuel bowl and installing an O2 sensor so you can see what is happening...Either way the lightest spring in the secondaries is going to wipe out the gas mileage...purple or long yellow is better for daily driving economy....(what kind of mileage did you get when it had the stock plain spring installed?)

If you fiddle with the carb, sometimes you also have to fiddle with the timing as well (if using a stock curve that will have to change).

-D.Idiot

I had a light yellow spring installed before and they were not opening at all same with anything heavier. That was before I started messing with it so I was getting 16. I have also had a lot of trouble with the float on this carb staying put. I was told it was rebuilt by a professional, but when I replaced the valve and seat, the problem went away.

Im thinking about swapping the Holley for a webber. How much performance loss would be expected? Im looking for 20 MPG, would the 38 38 get me there?

No, the last guy that tried one couldn't get ported vacuum, so with out ported vacuum your distributor curve is for not! no mileage gain.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG