So I'm new to the Carburetor realm so curious on your carb 302 setups.
I'm running a 302 with mild cam & 202 heads.
I originally was running an edelbrock 600 4 barrel single inlet & got around 10-12 mpg but the truck felt really restricted power wise. Had the carb wide open on the fuel adjustment (rich).
So I got ahold of a QuickFuel 750 4 barrel dual inlet in which I'm getting about 6mph but I have much better response & power. The truck seems to run the same gas mileage wise whether I'm running rich or real lean I still get bad gas mileage.
So my question is to balance out power & gas mileage what would be the best option? Replace the primary jets on my current carb (72) to maybe a 68? Or run a single inlet 650 carb? Thanks guys

 

When you say you "Had the carb wide open on fuel adjustment (rich)", do you mean you had the largest jets and smallest rods in it? Or, you just turned the idle mix screws all the way out? You must mean the latter as there's no way an Eddy 600 (1405 or 1406) can't be made to run so rich the engine will barely run - much less get 10-12 MPG.

My guess is that you are, as you said, quite new to carbs. Here's a link to the Edelbrock owner's manual that explains how to tune their carbs: http://www.edelbrock.com/automotive/...ers-manual.pdf If it were me, I'd put the Eddy back on and tune it as it is plenty of carb for a 302 - especially one in a truck and with your cam and heads.

Having said that, there are two Eddy 600 CFM carb's - the 1405 and 1406. The former is set up for power and the latter for economy. Their catalog says ithe 1406 is jetted something like 4% leaner than the 1405, which leads one to think they can re-jet one and have the other, but that's not quite true as there are differences that cannot be easily changed. So, what carb do you have? I ask because the 1405 will help noticeably on the top end over a 1406.

 

Yep, idle screws only affect the idle and a little bit of the part throttle.

 

This was the carb I was running. Had a buddy who builds motors tweek with the adjusting on it but the motor didn't run very smooth with this carb. Yes he eventually had to open up those front two adjustment screws all the way for it to run smoother.
I'm currently running a Quick fuel slayer series SL-750-VSF model runs great just drinks gas faster than an Irish man drinking at a pub lol

 

Yea this edelbrock carb would never allow my truck to idle on it's own w/o someone having to Apply the throttle to it until it warmed up. The quick fuel right out of the box made the truck idle better & response greatly improved. The edelbrock always felt like the motor was restricted power wise.

 

If all your buddy did to tune the carb was to open up the screws then you know where not to go for carb tuning. The only way to tune the carb, other than the idle air/fuel ratio, is to take the top off and change out the rods and/or jets. As shown in the manual linked to above.

The Quick Fuel, or any other 750 CFM carb, is too big for your engine. Sell it and use the money to get an air/fuel ratio meter, like the AEM or Innovate, and then tune the Eddy. It is a very tuneable carb that will provide good performance and great driveability.

Or, you could just start tuning the 1406, as outlined in the manual, by going to richer jets and/or rods for the Power Mode, and see what it does to your performance. Go to Ref #2, as shown on Page 12, and see if that improves the performance. If so, go to Ref #3 and see if it helps even more - although it'll probably be too much fuel.

The 1406 is more than capable of providing plenty of fuel for a mild 302 like yours. And yet it'll provide good driveability and economy when you aren't "in it" - something your QF is obviously not doing.

 

So, that proves my point. It means the Eddy's choke as not properly adjusted. It was too lean until the engine got warm - which is exactly how it is supposed to work. And, that's what the choke is for - to enrichen the mix until the engine gets warm.

The QF is so rich, even at idle, that you don't need the choke. But then it is running terribly rich after the engine gets warm - which kills economy. As for the increased performance, it is also so rich at WOT that the 302 likes it. So, all you have to do is enrichen the Power Mode on the Eddy to get the performance you want.

 

So pretty much all in a nutshell the eddy out of the box was running too lean for my setup & the quick fuel is the opposite too rich = overkill on gas?

 

Yup. If you'll read the Eddy manual you'll see that carb's have 4 "systems":

• Choke: This is to get the engine started and let it warm up until it will run properly on the idle or cruise air/fuel ratio. Yours isn't set right or you wouldn't have to be playing with the throttle until the engine is warm.
• Idle: This is determined by the screws out front, and just impacts the idle and low-cruise AFR. Your friend adjusted these trying to compensate for a lean power AFR - not gonna happen. Set them to 2 turns out initially and then adjust as per the book.
• Cruise: On the Eddy this is set by the combo of main jets and the larger step on the metering rods. This AFR must be about right or you wouldn't be getting the 10-12 MPG, although it may be a tad rich as you may be able to get slightly better. In any event, leave this ratio the same for your initial tuning.
• Power: On the Eddy this is determined by the main metering jets and the small diameter of the metering rods. This is what is apparently lean and you should use the info in the manual to move first to Ref #2 and test. If that's good but not quite enough try Ref #3.

 

Yes,, separate the different modes of engine operation like Gary listed above.

Idle screws are only for idle.

Cold engine starts are the choke's job.

Normal engine operation are the jets and metering rods

Wide open get down on it operation is mainly the rear barrels and that air door. If you feel like it was not performing when you got down on it, just loosening the spring on the rear air door might cure that.

You said you have a mild cam but how much lope does it have? You may need to put a vacuum gauge on it at idle and see what vacuum you are running. If it's really low and jumping up and down, this will let the needles in the main jets jump up and down and mess the idle quality up. If it's pretty smooth, then you are probably ok.

 

A minor change from the above - the 1406 doesn't have an easily-adjustable air valve. It is essentially the old AFB (Aluminum Four Barrel) and to change the opening rate of the air valve you have to remove or add weight to the counterbalance arm. But the later AVS carb (Air Valve Secondary), which is the Eddy Thunder series, does have an adjustable air valve, and that's what Dave was thinking of.

 

Thanks for the advise guys
So recent update... I was able to get a hold of a friends' friend that know his fords pretty well. He end up rejetting the 750 Carb (68 Prime/72 second) since I didn't want to spend another few hundred dollars on a small carb with the same size jets. Advanced the timing & installed the fuel regulator at 6 psi. Now i currently get 11-12 mpg & she'll leave elevens on the pavement! Very impressed for the size of the truck & the power it puts out now.

 

Glad you got that sorted. You got the MPG close to where it should be, and I'll bet the power is as good, if not better, than when it was so rich. Is the choke working?

 

Oh yea it's like night & day with this new setup
Yes it is.