Jetting a holley with some weird results

[OBL1V1ON]

ok i changed the primary jets on my holley 650 dp from 67 to 64 and the car seemed like it was doing fine. The plugs were clean with no pinging. However, when i would take the car up to 2000 rpm it would smutter and flop just like when you have a power valve blown. So, i put a new one in. No, change. The really weird thing is that after 2000 rpm it would clear up and hawl butt. Finally, i changed the primary jets back to the 67 and no more problem, at least no so far. Am i right in assuming that at around 2000rpm the engine was just not getting enough fuel creating the missing sensation, but past around 2000 rpm mark the secondaries opened (mechanical secondaries) up and let more fuel into the motor which is why i cleared up?

 

[AKRAY4PLAY]

you said your plugs were "clean", this leads me to think your plugs were white or close to it. if so, you're lean! the power valves don't kick in until there is a load on the motor and intake vacuum drops below the value stamped on the power valve. at 2000 rpm, you are depending heavily on the primary main jets. the idle circuit supplies all the time, but the mains and power valves add at different times. lean and stumbling conditions may not lead to pinging if your compression is low and gasoline grade is good. i would run the 67's, or bigger if the car likes it. Brian

 

[JohnZ]

64's are way lean for a modified 350 - that's what California smog air-pump 327's used in the late 1960's. I'd put 68's in it and read your plugs from there.