By Jove, old chaps, I think I've nailed it. I went for a short drive (to fuel up - necessary as I went through a tank doing this tuning etc. and managed a stellar 6 mpg!)
Idles very well, moves out on command, very sharp throttle response at street speeds, pulls like a tractor and doesn't diesel on shutdown. I don't know when I will have time for a freeway run but I'm looking forward to it. Idle is that happy, stable Let's-go-Boss, Let's-go-Boss.
Will also chirp the tires in second with no effort at all - I was just a touch aggressive off the line at one light, heard a funny birdie sound, realized what it was... then saw the ominous black motorcycle in the rearview. It wasn't a cop, thank Shelby. So I did it again coming home, this time checking six
first.
This all comes from a complete baselining and re-tune this morning. Final settings: 1.0 turns on the idle mix and long, careful experimentation with the primary butterfly setting and the Idle-Eze setting.
I don't think Idle-Eze does squat-a-roonie on my engine; the cam is milder than the problems it's supposed to correct. I ran it all the way open and shut at many butterfly settings and a variety of mixture settings, and at most it affected idle speed by an amount somewhere in the noise and flutter region. It was closed for all prior testing; I ended up leaving it open one turn and then redoing all other tuning around that.
Best idle (smoothest, fastest) was at about 3/4 turns, so I carefully reset all four screws to exactly 1 turn.
Idle speed was only adjustable with the butterfly setting, so I tweaked and tweaked for the smallest opening and finally got it nice and settled at a nominal 750.
Results already stated. This is with the long-oval air cleaner and a K&N filter - I can't fit anything taller than stock, so it's only got about an inch of filter area. I did some calcs and measurements and figure it's got about twice the area of the K&N in the little AC.
Final settings and changes overall, from the box-stock carb:
- Blue accelerator pump cam, much more aggressive profile than the stock pink.
- 1 turn open on Idle-Eze, probably has little effect.
- Careful mixture setting to best plus one quarter turn.
- Distributor changed from 15+21 to 18+18.
- Idle set higher than I was using - 750 instead of about 680+.
- Primary jets dropped to 74 instead of stock 76.
- Vacuum secondary spring brought down one step.
I will probably leave this untouched for a while, until I can get a look at some plugs that have actually been worked out. I will almost certainly work on the jetting, fore and aft, once everything else is settled. I might try the orange pump cam, which is about halfway between pink and blue with the gentler pink curve. (If I can save that fuel without any loss in off-idle response, I'd like to.) I might need to go back up one spring on the secondary, as I did get some hoppity-bog on the freeway yesterday... will have to see if it persists with the current tune. I may well have to change the power valve as well if I lean out the jets much.
I think I was right in the first place - not 100%, but the accelerator cam did the most to solve the bogging problem. Opening up the screws from "ideal" helped a lot, too. The distributor... can't tell how much it affected things, but given FEs' love of advance, it can't hurt. The higher idle was the last bit... that, and me learning not to be quite so soft on takeoffs. Being gentle on the pedal compounded the inherent problems.
Thanks
very much for all the input on this, gents. I didn't realize how much I'd forgotten about carbureted engines. Buy yourself all a round next time.
Bullseye!
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