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Jetting for reduced choke size, part 2

PostPosted: Thu Feb 27, 2020 11:09 pm
by webbslinger
Awhile back I posted about my car seeming to drive better on 135 mains after reducing the chokes from 34mm to 33mm. It had been running 130's with the 34mm chokes.

That didn't sound right and several of you expressed skepticism so I've been fooling around with it off and on. Finally good weather lined up with some time and now the jetting is at 130 mains, 185 air cors, & 50f9 idle jets. F 16 E tubes.

The 50f9's are a bit too rich by the afr #s, but not from a driving standpoint; it feels fine. I've tried 50f8's several ways but they are too lean.

Afr is now about 13 -13.2 under wot at redline in 3rd and around 12.7 -12.9 under normal hard (but not to the floor) acceleration. I tried 190 air cors but the afr went to 13.6 at wot and it sounded close to detonation. I might possibly back off further to 180s.

Anyway, I thought I'd put this out there as I like hearing how others problems were resolved.

As for afr guages: I have become a fan - particularly of the ones that log so you can download and compare afr vs rpm vs vacume.

Re: Jetting for reduced choke size, part 2

PostPosted: Fri Feb 28, 2020 9:44 am
by nmauduit
if you have not already, one thing you may want to fiddle with is the combination of idle (45F9 or 45F8) and one notch larger accelerator pump jet : you may then be able to run leaner at low throttle (do you get black spark plugs?) and still have the mix you prefer for sudden acceleration. Fine tuning is difficult to do just by the seat of the pants and AFR indication, so depending on your goal you may as well just enjoy it rather than spending a dyno session...

Re: Jetting for reduced choke size, part 2

PostPosted: Fri Feb 28, 2020 3:25 pm
by webbslinger
Thanks for your suggestions Nicholas. I read one of your other posts and if I got it right, it sounds like our engines are similar, at least in final hp.
The plugs look good. I think the ideal low speed jets for this motor might be in between f8 and f9. There is an occasional slight lean stumble while cruising with the 8s. It's still a work in progress and the pump jets are next. I definitely will dyno it in awhile, but I want it to be real close when I take it in. When done I will post the results and what the hp difference is for the reduced choke size.