Thread: 350 timing question

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This is a great forum. Hopefully you guys can help me look in the right my direction for my problem. I'll try and include all the info, and keep it as short as possible. My son has bought a low mile 350 shortblock. It is bored .30 over and has a cam with the following specs: Duration @.050" 227/233, Lift .489/.504 (LUN-60103LK). We put on heads with stock valves with double springs and roller rockers. hyd. lifters. edelbrock 650, 4 speed. Problem is we can't get it timed without a flat spot in the acceleration. I've read posts here on how to get this done and just don't get it. I started with timing it at 750rpm at 18deg, took it up to 3500rpm and I have ~40 deg advance in the dist. (does this sound right?). Timed like this there is a significant flat spot on acceleration, until the rpms come up, then it screams. The best it runs is when we set the timing @29! deg. At this setting the flat spot is almost gone but 29 deg can't be right. I checked that the balancer has not shifted or slipped. We checked that on #1 tdc the timing mark is dead on zero(on compression and exhaust both). My questions are (1) what symptoms would I expect to see if there was an intake manifold leak under the manifold(inside) we have done the starter fluid check all around the manifold/carb with no sign of leakage and (2) what if we missed the timing gear by a tooth when we installed it, or have you heard of partially shearing a crank timing gear key? would these give me the symptoms we are having? Any help provided is much appreciated. carb is mechanical secondary, and dist is HEI vacuum adv.
Thanks,
Mike