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lean surge at WOT

4K views 14 replies 6 participants last post by  FAIRMONT MIKE 
#1 · (Edited)
stock 460 engine; D3 heads; performer intake; FPA shorty headers.

3310 Holley vac sec. carb; 750cfm
main jets = 72
power valve = 6.5
secondary side has no jets; just the "plate"; #21
vac secondary spring is the "plain" spring (third stiffest setting)

It seems I need more fuel at WOT; do I need a "high-flow" power valve instead of the "standard" power valve?

Or would I just need a numerically higher power valve?

I have 15 inches of vacuum at idle with the auto trans. in gear.
Fuel pressure is good.

I dont get this surging behavior "off the line" so to speak; it starts to happen as the rpms climb up around 3500 rpm.
It will also do this when I mash the gas while cruising down the interstate; also around 3500 rpm.


Thanks-
 
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#11 ·
If the lean surge is truly at WOT then changing the power valve will do nothing. Enlarging the PVCR's will.
 
#14 ·
You can convert to a secondary metering block which will make the carb a little easier to tune. You may need a new fuel line depending on what you have on there now if you do.

The proper way to do this is to tune the primary side first by disabling the secondaries and finding the combination of primary jet and PVCR size that gives you good cruise economy and safe WOT A/F ratio then tune the secondary for WOT.
 
#13 ·
Here's a good read on carb tuning, http://members.tccoa.com/392bird/tuning.htm hopefully it will help or give direction prior to drilling on the metering block. This, along with an air/fuel meter gauge, help me tune my 770 Avenger which was too lean in a few areas. Todd
 
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