running .494 cam and now carb "runs out of gas"

[mudda_hunchie]

I have a 383 with a 600 edelbrock carb.  It had what I believe was the factory cam iin it, or the equivilant.  Lobe wore off the front of the cam so I went with what jeg's suggested for the biggest cam I could use without making any other modifcations to heads or anything else (.494).  Myself and another guy put in the cam.  It sounds awesome  at idle.  However, now at 3500 to 4500 rpm at highway (and faster) speed, it sounds like it starves for gas.  The guy that helped me said I needed a bigger carb.  Time rocked on and I recently purchased a 750 edelbrock from national carb.  With this carb, I would get a little more out of the engine, but the dang thing would flood at idle.  The national carb folks took my engine info and said the 750 wouldn't work on my engine setup.  My engine is pulling 9 in of vaccuum.  National carb guy says they set all carbs to run pulling at least 21 in of vaccuum.  Also been told to move to a larger (3/8) fuel line.  I sorta wish now that I had went with factory grade cam.  I haVE created myself a whole new set of problems.  Any thoughts or questions?

[flyinlow]

If you tee a fuel gauge into the fuel line near the carb and mount the gauge so you can see it while you drive. (Duck tape to wipor arm for troubeshooting) Eddy carbs like 5-6 psi. They will flood over 6 psi.  Determine if you fuel delivery system is providing enough fuel at higher power settings. A 600 cfm will not run out of gas just because it may not be big enough for peak power. It should deliver a 12:1 A/F ratio right up to 600 cfm at wide open throttle. You might be leaving some top end power on the table ,but the carb should run fine. Some models of 600 CFM Eddy carbs are jetted slightly leaner for better gas milage on Small Block Chevys. The 750 should work on a 383 with a cam that is a step ,or two more than the stock 383 Magnum cam.

Eddy carbs run well on engines with a milder state of tune. Say 10- 12 inches of vacuum at idle and above. Most street engines won,t have 21 inches of vaccuum except at higher rpms with a small throttle openning.

3/8 lines are a good idea. 

[mudda_hunchie]

Thanks  for the reply.  I don't know about the 750 eddie I had.  It didn't seem like to me it should be flooding unless something was stuck in the float.  Mayne the guy was just blowing me alot of smoke.  All i know is that particular 750 carb wouldn't work as well as the factory 600 eddie.

[maxwellwedge]

Did you degree-in the cam or just line up the marks? And I agree with flyinlow  - whoever the woodchuck is that mentioned 21" of vacuum should never be the recipient of any of your Benjamins.

[mudda_hunchie]

Just lined up the marks.  Guy that mentioned 21 in of vac owns national carb in Florida.  Didn't want to give my money back for the carb, but he finally did.  Just glad I didn't lose any more than shipping.