The two instances I remember, both had a 340 intake on an otherwise stock 318. In both cases, the ONLY thing we changed was the intake manifold, and the bad hesitation they both had disappeared. IIRC, (this was over 35 years ago, so, some details might be mixed between the two), the 1st setup was a '69 Dart with a '68-70 340 intake and a Holley 600 vacuum secondary. The head castings were the stock 675 castings. The rest of the engine was also stock, including the exhaust manifolds, single pipe system, and camshaft. We reused the carb and air cleaner without changing anything. Same distributor and timing specs too. The second time was basically a repeat of the first, except it was a '68 Barracuda that had a aftermarket dual plane aluminum 340 intake...I think it was a Wiand. Same size Holley, and the rest was also stock '68 single exhaust along with the rest of the engine. Both had aftermarket open element air cleaners with new filters (one of the first things we tried in order to get rid of the bog, including full tuneups). I never ran across that exact situation again, but, I got out of the retail repair business soon afterward, so, I expect I would have run across a few more if I continued in that type of work. No way to know for sure though.
