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I think you will have to richen up the transition circuit to cover up the hole between the accelerator pump shot and transition into the main circuit. Usually enlarging the idle restriction and maybe the power valve restriction in the metering plate by a few thousandth should help



I would agree with those mods...EXCEPT...this isn't the motor that carb is going to end up on...(assuming the 650dp is goin on the 340 when its done? I could be wrong in ASSuming there) ...plus its a one way street if you drill the PVCR larger and it doesnt fix the problem or worse...end up drilling too large and it results in a rich condition. Or ends up fixin the problem on the 318 and it doesnt run right on the next motor it goes on. Then your stuffing bent pieces of wire in the pvcr to try to reduce the flow thru an oversized hole or buying a new metering block...etc...

I always like to start with external easily reversible changes like accel pump adjustments, plastic cam changes and engine timing FIRST.

Its also possible the PVCR size is fine but it needs a power valve that opens sooner than the stock 6.5. Maybe an 8.5 or 10.5 depending on engine vacuum at idle and cruise. Its all trial and error....and can get expensive parts wise but if youre stickin with Holley carbs then you end up with a collection of parts you can use to experiment with on most 4150 series carbs in the future (power valves do eventually get hard though- ive got a collection of petrified valves).

As for drilling...I only go drilling idle bleeds, fuel bleeds and PVCRs as a last resort...and its usually bcus the carb selection was wrong.

I'm also guilty of the "spending lots of time tryin to make carbs and manifolds you have lying around work right" scenario than I'll ever admit too. Oh mannnnn I just did.... DOH!!!!

Make adjustments, change parts...or drill baby drill... I guess it all depends how much time, money and patience you have

As always.....YMMV