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Old 06-17-2013, 10:27 PM
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new here need sbc timing/vacuum advance help

I have a fresh 421 sbc brand new everything including hei distributor. Howards hydraulic roller cam close to 600 lift w 1.6 lifters (still makes good vacuum based on specs for sure and I can verify it does) Holley Ultra Billit 770 carb on Vic jr manifold. 10.77 to 1 using gapless top ring.
OK> problem is setting timing at 10 at idle of 950 w no vacuum advance hooked up and goes to 34-35 at 3500 to 4000 THEN I hook up the vacuum advance and it jumps to 38 to 40 at idle?!?!?
Also getting some popping/backfiring off idle when throttle is applied? ?? WT (HECK)? Howards said to set lifters at 1/4 turn pressure and I set them at about 1/3 turn from zero lash ( could they actually be staying slightly open from this tiny amount extra and be creating the backfires? )
New to this whole sbc gig so any help would be great for sure.

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Old 06-17-2013, 10:35 PM
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Quote:
Originally Posted by Cambertire View Post
Also getting some popping/backfiring off idle when throttle is applied? ?? WT (HECK)? Howards said to set lifters at 1/4 turn pressure and I set them at about 1/3 turn from zero lash ( could they actually be staying slightly open from this tiny amount extra and be creating the backfires? )
New to this whole sbc gig so any help would be great for sure.
If you adjusted the valves by twisting the pushrods against the spring in the lifter, they are too tight. Nobody but a builder who does this every day, all day long, will have the finger feel to get the lash right. Use the "jiggle" up and down method.....
http://www.crankshaftcoalition.com/w...stment_SBC/BBC
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