Thread: HEI advance curve

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Because my dad lost low end power with the HEI he recently put in his '72 350, and it is backfiring through the carb more than ever, he bought a Advance timing light from HF and wants to check to make shure the curve is right. I googled for advance curve specs to set it at/ check for but no 2 are alike. what is a normal advance curve for an HEI?

Originally Posted by Matt167

Because my dad lost low end power with the HEI he recently put in his '72 350, and it is backfiring through the carb more than ever, he bought a Advance timing light from HF and wants to check to make shure the curve is right. I googled for advance curve specs to set it at/ check for but no 2 are alike. what is a normal advance curve for an HEI?

you buy the curve kit you want, and all you can do with the adv. timing light is check for total timing. far as i know, to check to see what curve you have, you need to get someone thats set up to do that. i don't believe a adv. light will check the curve. the curve and how soon it comes in has more to do with racing than st. get your base timing, and check you total timing and thats all you need for the st. be sure the vac. adv. is working. backfiring sounds like its late in timing or running lean.

with the old points distributor it used to backfire twice through the carb when it was cold, if ya stood on it, and then that was it, but now, it will do it whenever it feels like it, if you get on it. the vac advance is hooked up to ported vac. Thanks

Originally Posted by Matt167

with the old points distributor it used to backfire twice through the carb when it was cold, if ya stood on it, and then that was it, but now, it will do it whenever it feels like it, if you get on it. the vac advance is hooked up to ported vac. Thanks

whats your base timing and that is you total timing?

havn't had the adv light on it yet but base timing was set at 8* BTDC, factory specs. we played around with it but then just set it at 8*

Originally Posted by Matt167

havn't had the adv light on it yet but base timing was set at 8* BTDC, factory specs. we played around with it but then just set it at 8*

check your total and if thats right you should be able to leave the timing alone and go to something else. is it a QJ carb?

yep, factory Quadrajet

Originally Posted by Matt167

yep, factory Quadrajet

i got a feeling the popping back is in the carb. check your pump shot, take up any slack that the arm might have. need to make sure the power valve is free, and the secondaries are working.