Hi! running a new 350-330 hp crate engine,performer rpm manifold accel hei distributer proper coil edelbrock 600 cfm. incredibly bad flat spot in primaries, have to feather gas pedal to avoid and if i put my foot in it will backfire thru carb. plugs burning ok sometimes rich manifold vacuum at steady 16 at idle, runs smooth if accelerate slowly. idle adjustment comes in smooth. dont think its a manifold leak. Carburetor? Thanks

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sounds like a bad accelarator pump.

i had the same prob in my nova with built 355...check voltage to coil. i got rid of my flat spot by simply putting in a late model alternator(cs 130) that kicks out steady 14.6 volts with everything running in car, and bog is totally gone..i put alternator in just cuz i had it and read how to do it in car craft or something, and was gonna rebuild carb next weekend. guess there is no need to mess with carb.oh yeah- did you take out that factory resistor wire that goes to coil? it kills about 3-4 volts, and will cause it to run crappy...

I have a good one about HEIs and not enough voltage. When I bought my 79 Vette it was apart with a blown engine. I put new 350 but being in Cal it had to smogged so all the smog equipment went back on. The batt was dead so I bought some cheap one at Sams club to get it running. I played with that thing forever it just would not run right. I finally just figured that was how a smoged motor ran. The thing would always kill the bat when it set for awile I just thought standard Vette electrical problems. Finally I couldn't get the batt to charge at all so I checked it out one cell was dry and appeared to have never been functional I had a 10 volt batt from the start.Apparently the alt. was trying to make the batt. a 12volt instead of a 10volt so that there wasn't enough voltage to run the HEI. Put in new batt. completely different car a vast inprovement in performance. I don't know if you are running the HEI off of the origonal wire to the coil but don't it needs a full 12 volts

Start simple i had the same problem when i bought my 69 i just adjusted the air fule ration on the carb and it fixed everything. also check timing if these things are ok then u can look further

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69 Camaro RS, 355ci mild cam, Preformer rpm intake, edelbrock 600 carb, 350 turbo w/ shift kit 2500 stall, 10 bolt 2.73 any more questions ask

have the distributer RECURVED!!!! i never claim to be a know it all but i hope some day to be close!hahaha.i like to learn new things ALL the time,sooo this weekend i decided to pick up a book on IGNITIONS. BOY,i never knew how much of a difference a well set up ignition makes(i was really thinking the wrong way ALL the time)did you know that TOO strong of a spark can cause a misfire? i didn't i thought the more the better. it was written by DR. jacobs(yes he makes the jacobs ignition) and what blew me away was how he didn't praise his own but exsplained how all manifactures ignitions worked and worked good! i HIGHLY recomend getting this book,it will change the outlook on how you view ignition systems FOREVER! i'm very excited if you couldn't tell!!

I have a very simular setup. It took me some jeting combos before I got it just right. Tinker with that carb.

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Stock 67 327 RS
http://angelfire.com/ca7/goatjjcamarors/pics

I'd look at the carb first, then look at the distributor. The accelerator pump is probably the culprit. The backfire through the carb means too lean, and is not usually a timing/curve problem. Just look in (with the car off) and watch the squirt from the accelerator pump to start - I bet you you'll see there's either not enough gas or the squirt is erratic when the accelerator lever is operated.

Check your timing...12 degrees initial will get you in the ballpark. Make sure the vac advance or mechanical advance is working properly and not frozen in an advanced setting. Set your accel pump rod closest to the pump arm pivot and see if this helps...if the 600 edel on my truck has the pump arm all the way out, I will get a light pop back thru the carb when I punch it. If that does no good, try swapping in a 7" step up spring (stock is 5")...this will bring the primary enrichment in sooner. If still backfiring when you punch it, try going a bit richer on the primary rods (power mode). The manual that came with your carb covers all the details on setting one up...you will need to purchase the edelbrock calibration kit...it will be money well spent. If still no good, try moving your vac advance vac source to the other port...if your using manifold vac for your advance try using ported instead (or vice versa). One last thing...are you using the 1405 or 1406? The 1406 is jetted leaner and will have more of a tendacy to pop back thru the carb...but the calibration kit will help take care of that. Hope this helps.

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375hp 78 Chevy truck
77 Chevy Nova
95 Chevy Lumina 3.4L
and building a 78 Nova

Sounds like accel. pump adjustment. They have 3 holes in arm for rod positions.Try the bottom hole for longest squirt. Good luck! http://hometown.aol.com/zz430droptop67rs/

actually the Accel HEI is supposed to have 24 degrees mech advance all in at 2500 rpm. Make sure your accelerator rod is in the top hole for the fastest shot of gas. You can also buy bigger accerator squirters from jegs