Anyone else has the offy intake with edelbrock 500 have idle issues? I set my timing and tuned it runs great but seems real rich at idle and the idle screw is all the way backed out? Anyone else have similar results? Why would it operate this way?

 

Check fuel pressure at the carb. Edelbrock carbs don't like more than 5.5-6 PSI.

 

Check for vacuum leaks while you are at it.

 

Spray for vacuum leaks all around the base of carb. Disconnect and plug the vacuum advance. I'd set the timing with a vacuum gauge. The vibration dampener may have slipped/moved. Make sure the engine is completely warmed up to running temp. Check gasket interference by gently moving the throttle closed by hand. Does it close more when moved by hand, making the rpm fall, than it does when you're working the pedal? If so you've found the problem. You might want to install another spring or remove the carb and check the gasket for interference.

If that is not the problem I'd set the mix screws. I'd turn off the engine and GENTLY tighten each screw all the way in. Gently. If you tighten too far you'll strip the threads and the screw will pop out, signaling you're up the creek. Loosen each to 1 1/2 turns out, then start the engine. Turn up the idle if needed. Tighten one at a time, in 1/4 turn increments, until the engine starts running rough, then back it out to the point where it runs smoothly, then do the other screw the same way. A vacuum gauge really helps you find the ideal setting, even more so a AFR gauge, but you can do by ear and feel.

 

I'm running 4.5 psi on pressure and checked for leaks with carb cleaner. I set idle and carb idle mix with vacuum gauge. Running just under 20 with a shaky needle + or - 1 just seems to be comfortable running at this setup but it was bothering me. going to try to heat the offy intake with a coolant setup soon and possibly recurve dist.

 

What do you mean vibration damper? What affect would this have?

 

Download and read the Edelbrock carb tuning manual all the way through and follow its instructions.

 

That is a valuable bit of information.

Regarding the vibration dampener: The timing mark is on the dampener. The big heavy 'casing' of the dampener is rubber mounted and notorious for slipping on older engines; hence problems setting timing with a light. A vacuum gauge doesn't lie.

 

I'm thinking the carb heat will help. I have the same problem with my unheated clifford intake. Planning some carb heat soon.....

Also I personally think 500 cfm is too much carb for a stock 300.....I had a 2 bbl on mine for a while which seemed to run better.

 

The holly 390 is expensive are there any alternatives? The edelbrock works so no reason to replace yet but its quite rich at idle.

 

Look down into the carb with the engine idling. Is there gas leaking or gas puddling anywhere? A float may be sunk. If you have adjusted the idle mixture screws according to the manual and it is still stupid rich at idle a bad float would be my first guess.

 

Thanks baron! I did not think of that now that you mention it when I rebuilt the carb it seemed like one float was kinda touchy and didn't drop/raise as well as the other could be sticking...

 

Not really. I don't know why people think that. How many guys do you know that run a Holley 390cfm 4V on a 302 V8? The 300 runs quite well with the 500 cfm carb. The Edelbrock carb has an air flapper valve on the secondaries. So the secondaries are only going to get the extra air flow when the engine needs it.

 

+2 what Ted said. It seems that the misconception comes from looking at the total flow capability of the carb and somehow thinking that the engine is going to use or be forced to use all that capability. It just ain't so. A 4v carb is nothing more than a 2v carb with an auxiliary power circuit of 2 more vs. On a vacuum or air-flap actuated secondary carb the secondaries (when properly adjusted) do not even start to open until about 2500 rpm-3000 rpm and on most of our engines will not ever see full opening of the secondaries even at 4000 rpm-5000 rpm. The carb does not determine how much of it's capacity the engine will use...the engine determines that.

 

Good info. Thank you