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I had the exact same problem. Engine would run fine until 4200 rpm, then it would cut out. I checked over all of my timing, wires, plugs, etc. Nada.
Several months later, I had the car up on the lift looking things over in preparation of an in-tank fuel pump/tank for a FiTech fuel injection install, and noticed the kinked line.
I changed it out and the 'bang' ran all the way up to 5800/6000 without a problem.
thank you i will certainly look into it .i do know all the lines were replaced before i bought it ,but its certainly possible one could have been kinked in the process.
update if anyone is keeping track .we spent a couple hours going over everything yesterday checking rotor ,cap ,wires , voltage to the hei ,fuel lines etc.we pulled the distributor and restabbed it one tooth over to get the vac can away from the firewall.ended up at 24 degrees btdc ,with easy starting while hot and no pingging.did make some carb adjustments as well .cant get the car to duplicate the issue.it will stumble a little at wot in low2 but its at speeds near 95 mph .i think with this original 76 quadrajet its not delivering sufficient fuel . im completely happy the way it runs though.not sure of the hp increase we got from the upgrades but i can say its considerable .yesterday was the first time she started getting away from me laying down the first posi marks of the season pretty impressive for 256's out back
I think you'll find that with your 24* initial setting +21* of mechanical advance thats normally built in to an HEI will put you way over an acceptable range at your top end and you will have detonation. Then add the 10-15* of vacuum advance puts @ min of 55-60* total with vacuum at cruise you may get surging and pinging at medium throttle.
I think your engine may be happier if you set your timing so that your total without vacuum (at what ever RPM it stops advancing) is no more than 34-36*, with vacuum no more than 50-55*. Let the initial be what ever it winds up to be at those settings.
Get one of these, they can be had through any performance outlet store. It's used to limit the travel of your vacuum advance. It takes the guess work out of it. Follow the instructions for your particular adjustable vac adv can on how much vacuum it takes for it to operate correctly.
took the car a couple hundred miles yesterday,ran really well with no issues .62 lbs of oil pressure at 70 mph and 2500 rpms,and the temp ran at 190 all day.Amazing how nice the ride was (will be redoing front suspension at some point ) the engine isnt a night and day transformation from its original smog state ,but is noticably more powerful .i suspect a gear change would would make a big difference. With the available torque it will still smoke the tires nicely with the 2:56 gears .thank you all for helping me out on this one .
April 13th, 2017, 03:34 PM
pretty impressive for 256's out back
