well,after spending some time playing with the jetting,i found myself stuck choosing between 2 jetting scenarios',and i didn't like either.
i've seen 3 different #'s on the jets in these 4180's. 209,309 and 602. 602 is supposed to be a close tolerance #60. i assume the other 2 numbers are fords numbers for the same jet. problem is,a 60 main jet should have a .060" hole,and these are considerably smaller. a couple thou' smaller,which is a lot relatively speaking.
with the stock jetting,it cruised ok,slight surging. and it pinged when i got into the gas,and it lacked the punch when i really stepped into it. but it got real decent mileage.
so i stepped it up several sizes on the mains,and the punch returned. the pinging stopped too. the mileage ceased as well.
so,as it was i had 2 choices. good mileage with poor kickdown punch,and needing to retard my timing to avoid ping,further decreasing power. or,jet it up to have power,and losing economy.
i wanted the best of both worlds,and here is how it is done.
the main jets are what you cruise on. that is why jumping up on them killed my mileage. i drilled a set of stock jets out with a .059 bit,making a #59 main jet and installed them.
the fix lies in the PVRC's. Power Valve Resriction Channels. they are behind the power valve. these are the "second" set of jets that are allowed to deliver fuel when the power valve opens.
i measured the PVRC's on a couple metering blocks i had around,from 600 and 750 cfm holleys. they range from .051 to .063. so,that means when the power valve opens,it's like having a second et of jets,sized 51 to 63,on top of the main jets,supplying extra fuel to the mix.
then i measured the 4180 block. they looked large. too large. a peak inside showed they were counter bored,and considerably smaller inside. to the tune of about .040. it's hard to see in the pic,you can barely see it. the inner hole is about half of the visible hole.
the fix is to open up the PVRCs',changing only the power jetting,not the cruise jetting.
i opened the PVRC's up to about .045-equal to about 4-5 jet sizes over the stock .040 holes,and the punch returned,and the pinging stopped,allowing my timing to be set to it's optimum setting. economy returned too.
i'm getting consistent 13.5+ mpg. i'm going to jump up a bit more on the PVRC still though,.048-.050. it'll need it when the headers/dual exhaust go on.
this is the one and only place the Carter AFB design offers tunability over the holley. however,i want to stress this procedure is RARELY NEEDED on a holley. this carb was an emissions carb,hence the small channels. all you guys running universal holleys,like the 1850,3310,or avengers-DO NOT TRY THIS! it is almost 100% not needed in those models. once this procedure is done,you can't easily go back.