Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
1903 Won't Respond to Tip-In Procedure
bry593:
Since my last post, I've wired the secondaries shut and have been driving it back and forth to work. No issues although it has a little lag, under part throttle with the choke still on. Once warm, runs like a 2-barrel. No sag or surge, but noticeably less power when pulling into traffic. I have also tried WOT and found nothing out of the ordinary.
Having the 2ndys wired shut lowered warm idle a few hundred rpm. I assume this is because the wire is holding the throttle plates more closely shut. This results in less air getting into the engine.
As for detonation, there is some slight ping from the vacuum advance while in transition mode. This morning, I plugged the Vac advance and will run some additional tests to see if the ping is solely due to vac advance.
Ordered some colder spark plugs. Changing from R44LTS, to MR43LTS. The "M" means marine, so has a stainless steel body. Will see what affect these have on ping. If not enough, might retard the timing back to 8 degrees BTDC.
Here are the rods and jets I am considering and % fuel change relative to current setup:
Rod Jet Cruise WOT C Area WOT Area Cruise % WOT %
50M 0.073 0.050 0.036 0.0022 0.0032 -4.94% -3.52% <<Stock 1903
50C 0.074 0.050 0.036 0.0023 0.0033 0.00% 0.00% <<Current
48K 0.073 0.048 0.026 0.0024 0.0037 1.65% 11.32% <<.006 Taper, Step to .026
45C 0.072 0.045 0.026 0.0025 0.0035 6.15% 7.85% <<Single Taper
45C 0.073 0.045 0.026 0.0026 0.0037 11.02% 11.32%
50P 0.074 0.050 0.026 0.0023 0.0038 0.00% 14.83% <<.012 Taper, Step to .026
bry593:
LOL, figured out why my idle was a couple hundred rpm lower. Remember when I said I disconnected the vacuum advance this morning? Ha, I'm an idiot.... :D
I plan to modify the advance stop window so there is absolutely no advance until 10 in Hg. I can do that by applying the mighty vac, pumping it to 10 in Hg, and then welding a sheet metal stop over the gap between the pull rod and end of window. I might even see if I can lengthen the other end of the window so it stops at 2 in Hg below my idle vacuum (19.5 - 2 = 17.5 or 16-17ish). Hopefully there is enough stroke to accommodate moving the window stop. Seems like this should work. Will let you know how it turns out.
I think most HEI advances are made to work with smogged, detuned engines of the 70's and 80's. That's why I can't find anything that actually matches my ideal: starts @ 10, and all in at 17, with 18-22 degrees at the crank.
Pav8427:
FWIW. Do a search for Lars Grimsrud HEI timing papers. He has a pretty extensive list of factory VA's.
Might be something in there that suits your needs.
bry593:
Thanks PAV, that is good advice. I didn't want to bring it up on Cliff's forum, but yes, Lars has great information on tuning the Quad and distributor.
At this point, I've pretty much read everything on the net: Lars, Cliff, Wallace Racing, Tuner @ Racing Fuel Systems, etc. All are pretty sharp guys, but do have varying viewpoints. Lars doesn't discuss calibration of the idle circuit, Tuner likes the idle circuit lean, Cliff likes rich since rich runs, Wallace must be an engineer 'cause he has a calculator for everything.... :D
I'm stubborn as hell, and have to learn things by doing. So I take everyone's advice and then do what I want. Win some, lose some, but always gain experience. I'll tell you, I'm almost to the point where I will follow Cliff's advice to drop in the ZZ4 cam... almost.....
Kenth:
I have found chasing a "magic" timing curve to ignite a too lean A/F mixture is a waste of time and leaves you endlessly chasing your tail, and an engine that will never run right or at it´s full potential.
Been there done that.
Nowadays i mostly use the proper factory timing curve, or very close to it, per engine application and add proper amounts of fuel into the mixture were needed, idle, off-idle, main and wot circuits, the engine will tell you were the need is.
Hesitation is an indicator of a too lean A/F mixture, and so is pinging.
Hats off for Cliff sharing his hands on experience with these things!
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