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lets start with what i got so far. a mild build up on a 402
30 over with stock heads and crank. piston are a half domed federal mogul
stl-402p30 from summit.cam is a gm cam i;228 e;238 @.050 max i;540
e;540 w/114 center lobe.1969 cast iron intake with a summit performance
quadrajet 750 cfm and flowtech headers with magnaflow 2.5 inch
exaust with x pipe.iginition is a gm performance hei dist and a stock gm
fuel pump.what im running in to is this.the motor will not idle right like
it has a vacum leak or the carb is junk.i can let run for a while down
about 800 or so rpms and seems to be fine.it revs with no hesitation
and sounds good.the idle will pick up by it self and it does not matter
if you screw both screws all the way in it does not change on the carb
wich sounds like a vacum leak to me but i sure cant find it.i resealed
the intake took carb a part checked everything cleaned it out blew air through it.put it all back together and the next day cranked it over and
it fired right up and idle for 30 seconds and died.right back to where i started
i can get it running good at a idle and turn it off for a minute and try to start it again and completely diffrent . will not idle.i need a nother carb i dont think that cam would have anything to do with it.
 

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Couple of things I can think of. The HEI may have real weak springs that allow the timing to start advancing around 800, you need to verify the idle timing. Also, that cam will still pull a lot lower vac at idle, the vac advance canister may need to be changed. You will want 36-38* total timing and at least 20* at idle, more if you can get it. Other than that, check everywhere for vacuum, leaks. If you have to, disconnect and cap off all vacuum ports (brakes, trans, etc) until you get things sorted out.
 
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