So, I found a deal on Craigslist for a Holley 1850 600cfm (vacuum secondary) carb for really cheap, and I am considering buying it.

A friend keeps telling me that we can jet down the carb to make it work right for my 300/6. Will this work? Do they even make jets small enough to get it adjusted right? Or is fuel delivery not the only problem with using a carb that is too big?
Has anyone done something similar? Any insight? Should I just spend the $280 for a new Edelbrock 500 (or is that too large also)??
Thanks!!

 

The absolute last adjustment to make in a carb and then if only needed after pump shooter adjustment and secondary opening adjustment if needed is a change in jets. High altitude areas (like CO,WY, etc.) usually do call for a jet adjustment but not nearly as much as one might think.

In theory, no carb is too big and then it is usually a matter of adjusting the secondaries to where they do not open to early too quick. And until the engine is turning upwards of around 3000 rpm or more the secondaries won't even open which leaves one running on the primaries just like a 2v carb.

 

OK, so it should be simpler than I thought? Would I be losing out on fuel economy with a carb this size?

Also, am I really only going to see the secondaries opening >3000 RPM? I really won't see any benefits in that case then, as I never rev over 2000 when shifting, and I rarely go above 2500 when cruising in 4th.

 

Below 3000 RPM, a 300 just can't pull enough air to need the secondaries open on a carb this big. And they certainly won't have enough velocity in the primaries to open the secondaries.
This is why the 390 and 465 CFM holley carbs are much more popular on a 300. Heck, a 600 CFM will feed up to 400 CID at 6000 RPM, so it's mega-overkill on a 300 I6.

 

At those engine speeds you will be running on the primaries...basically a 2v carb situation. MPG is as much or more a matter of driving manner rather than just the carb itself.

 

Then I guess I'll pass on this deal, and just spend the dough on the Holley 390. One of the bigger things from this swap that I am looking forward to is the kick in the *** the secondaries give you.

Thanks for the advice guys!

 

Technically, the "kick" is due to a momentary lean condition when the secondaries are opened and when the fuel flow hasn't caught up to the air flow...essentially the same as a "tip-in" stumble.

 

Technically, anything is going to be better than pinning the throttle with my 1bbl, and getting no more result than an increased whoosh out the exhaust.

 

The Edelbrock 500 is a popular and fairly easy set-up. Some even use spread bores like a Quadrajet. There again, the carbs are not "too big" as they can be adjusted to what the engine will utilize with plenty of change left over.

 

X2
The 500 Edlebrock (Carter AFB) is what I have on my 300. I had a 600 carter AFB on it to test it out and it worked ok as well.
Many aftermarket carbs are a littel rich right out of the box so you don't burn a piston if you have an odd combo.

 

FWIW, the Eddy 500 and 600 carbs are exactly the same other than the jets, rods, and pump nozzle.

 

Stellar!

I'm running the Edelbrock 500, after trying a spread-bore Holley and a Quadrajet. It's jetted one step leaner than stock on the primaries, and two or three (I think three; I can't remember off the top of my head) on the secondaries. Driveability's really good, performance is way better than the 1 bbl, and mileage is decent. It's also one of the easiest carbs to work on I've experienced. Free advice - spring for the AVS, which has adjustable secondaries; the Performer doesn't, and the factory setting is not optimized for our application.

 

The AVS is a nice carb...especially the adjust-ability of the air flap.