You know your vacuum so I assume you have a vacuum gauge. Does it show a
stable vacuum or is the needle erratic? Backfires through the carb? Don't
sound real good, COULD mean something in the valve train. I could probably
check old messages but is this a fairly new motor assembly, have you
adjusted the valves? That vaccum gauge can tell you allot about what is
going on in that engine.
Ok... So I am back to work fighting this damn carb... so here we go
Edelbrock 1406 (600cfm) on a 350ci/290hp motor...
Cam: ".450'' intake and .460'' exhaust lift", and "Flat Tappet Duration
@ 0.050'': 222° I, 222°"
1986 K5 Blazer, emissions stuff not connected. Vacuum to brakes, PCV,
and vacuum advance (ported).
13" Hg of vacuum, 8 degrees BTDC at idle/850rpm.
I've been playing with changing the metering rods and jets, and I'm
making progress with it. I should have it running pretty good soon.
I'm getting good results with that but need another couple sets of
metering rods to try out.
Anyway, it STILL does not idle to my liking. I am having the damndest
time with it.
Initial timing was 16 degrees BTDC (really). While idling, I brought
it down to about 8 BTDC, leaned out the mix a 1/4 turn on both screws,
and reset idle speed with the adjustment screw to 850rpm.
I thought, maybe closing the idle screws in to 1.25 turns (from the
recommended 1.5 turns) combined with increasing the idle speed would
help. It has a little, but beyond that it gets really irratic. Vacuum
continues to drop.
If I set the idle for max vacuum, it just gets richer and richer, and
the timing gets more and more advanced to compensate. I suppose if max
vacuum at idle were the goal, then I could achieve that easily, I have
before. But it SHOULD NOT burn your eyes out because it's running so
damn rich at idle.
I later took the idle mix screws in to 1 full turn out...a 1/2 turn
less than recommended as the starting point. I hit the gas once, and
it backfired through the carb. At this point I'm gonna have to replace
my air filter, as it's the foam type and now it's showing signs of burn
damage on the inside (it's singed and shriveled up a bit).
WTF am I doing wrong here? I just want it to idle at the right mix.
Or is this carb just FUBAR? Was a 600cfm Edelbrock too much for my
motor? I know the stock carb on the old 305 was a 795cfm carb, but a
Quadrajet is a WAY different beast, so I don't know if cfm's would be