Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
1903 Won't Respond to Tip-In Procedure
bry593:
For those reading this thread, be aware changing a jet changes both cruise and WOT response. On the other hand, rod changes on a 170, do not change WOT. The end of the rod, when the power piston has risen against the airhorn gasket, is still the same size..... So, apparently I need a 75 jet change to fix ping in the primaries.
Cliff Ruggles:
No need to change the metering rod that would have ZERO effect on any heavy/full throttle.
To test PRIMARY size jetting do NOT use the secondaries.
Climb a steep grade in a higher gear and lug the engine down while heavy on the primary side and not into the secondaries. If it pulls hard without any lag or feeling "flat" on power the jet size is adequate.
Most likely it just needs a little timing pulled out of it.
Keep in mine that with a tiny cam on a tight LSA and 383cid with decent compression cylinder pressure will be spike pretty high in the mid-range and early. I'll bet the hardest pinging will occur around 3000-3200 rpms at heavy/full throttle.
You may also find some light pinging trying to add much timing from the VA as well......
Kenth:
Did you disconnect the secondaries during this last test?
bry593:
I did not block the secondaries. I simply mashed it to the floor and it started pinging immediately, so got out of it.
Would AX secondary rods prevent a lean condition in the secondary? The AX have long, thin tips and are about as rich as you can get.
Have not yet mapped out Cliff's advance. Will wait until the new advance arrives and check both the same evening.
bry593:
If I do find that the primaries need richened, there are still rods available with a smaller (.026 vs .036) power tip.
Here's a table listing % change in fuel relative to rod and jet:
Rod Jet Cruise Rod WOT Rod Cruise Area WOT Area Cruise % WOT %
50C 0.074 0.050 0.036 0.0023 0.0033
50C 0.075 0.050 0.036 0.0025 0.0034 5.01% 3.56%
50C 0.076 0.050 0.036 0.0026 0.0035 10.08% 7.18%
47K 0.072 0.047 0.026 0.0023 0.0035 -0.03% 7.85%
48K 0.073 0.048 0.026 0.0024 0.0037 1.65% 11.32%
49K 0.074 0.049 0.026 0.0024 0.0038 3.33% 14.83%
If I were to make a change, it looks like 48K rod with a 73 jet is a safe bet.
EDIT: Forgot to mention, I got close to 18mpg on the highway last weekend. So, I do like my lean calibration and it seems to be working. Just need to fatten the primary WOT I think....
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