I am having an issue with a misfire around 4000-5000 rpm under moderate to heavy throttle application in my big block Duster. Some of you might be familiar with my setup by now, but here it is anyway: '77 400 big block bored .030 over 9:1 compression Summit 282/292 hydraulic cam edelbrock RPM intake manifold Holley 3310 (750 cfm, vaccuum secondaries, dual feed) #74 jets on the primary side 6.5" power valve This problem was absent or not noticeable during the warmer months, but is very pronounced with the lower temps lately (it was 35 degrees today). I suspect it is leaning out slightly on the top end and this is exacerbated by the cold weather. Should I consider going up another jet size, or should I look at the power valve? The engine only generates 9-10 in/Hg at idle in gear, so the 6.5 in/Hg power valve should be adequate, right? Thanks!