Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
1903 Won't Respond to Tip-In Procedure
bry593:
--- Quote from: Kenth on March 03, 2021, 01:30:28 PM ---I would proceed adjusting the choke pull-off to open the choke blade a little less, about .160", measured between upper end of blade and rear wall of choke housing and increase fast idle speed some to keep it running.
For off-idle respond at least .052" idle DCR´s will help.
--- End quote ---
I did consider closing the flap a bit more and that was probably the right thing to do. I had previously set up the choke flap with a 1/4" bit per typical Quad specs (and an 1/8" inside the coil housing). But, opening the IT from .031 to .033 did do the trick. But now, wouldn't you know it, got a new problem.
Now, when the engine is warm and I stop at a light, the idle is fine for about 10 seconds. Then suddenly, like someone is flipping a switch, the idle stumbles and tries to die. I can pump it a few times, bring the rpm to 2000 and it clears out. But then once it returns to idle, it runs great for about 10 seconds, then like a switch tries to die. My first thought is that the air horn gasket has become fuzzy around the power piston from the many times I've had to remove/reinstall. Maybe some of this fuzz has circled the drain (the jets) and is plugging up the feed to the idle tubes? I can't think of any other reason it would act like a switch (unless my needle has gotten damaged, but I don't think so).
Tonight, I'll pull the jets and idle tubes and blow out the channel. Might as well solder the tubes back to .031, reinstall my .041 UIAB, and bend the tang to put the flap @ .160. I'll check the gasket and replace if it looks fuzzed up.
Kenth:
Are you setting the mixture screws with hot engine, in gear at 700 rpm´s.
How far out are the screws at best lean idle setting?
bry593:
Yes, I take it for a drive, get the stat open, then adjust the screws for highest rpm but on edge of lean. When I had IT .031, UIAB .041, screws were out 3.0-3.5. Now that IT .033, UIAB .052, screws are 4.0-4.5. I thought maybe it would go the opposite direction with larger orifices, but the screws are farther out now.
After adjustment, I set idle screw to about 750 in park and it drops about 100 when put in gear. Nothing odd about that.
On a side note, this carb has some casting irregularities down near the jets. No obvious porosity, just some lumpy looking areas. I might see if I can lower my air pressure as low as possible, fill the bowl with water and blow thru the idle tube channel with my finger over the jet hole. Just to help retain my sanity a bit....
Kenth:
I would have stayed with .031" IT and .041" UIAB.
Enlarging the UIAB´s to .052" and IT´s only to .033" will make the blend leaner than the previous. You may need at least .035" IT´s for .052" UIAB´s.
Also, .052" or thereabout DCR´s will make for better control of mixture screws and cure any off-idle issues.
JMHO
bry593:
I measured my fuel pressure and found it to flutter per pulse, between 5 psi (must be a checkball in the pump?) and 9 psi. I then noticed the airhorn gasket was soaked with fuel. It was flooding at idle and was the cause of my on-off switch at a stop light.
The carb was removed and I went to work figuring out what was going on with the float. First off, the air regulator was set to 9 psi dead head. Note that I double checked the pressure using the same gauge I used to measure the fuel pump pressure. Then the bowl was filled with gas up to about 1/4" from the top of the casting. Air was applied to the fuel port and bubbles came out under the needle. This was with the float set to 9/32".
The needle was removed and the seat peened with a checkball. The needle and float were reassembled and 9 psi applied. Still bubbled. I put my finger over the needle and it stopped bubbling. Apparently, not enough force on the needle.
I then removed the float and started bending and reassembling until it quit bubbling at 9 psi and the fuel level was about 3/8" from top. I thought maybe I should add a little safety factor, so I bumped the pressure to 10 psi. It quit bubbling at about 5/16" from the top. This float level ended up being 3/8".
Edelbrock says the 1910 should use a .300" setting. I looked at all the fuel pumps on RockAuto and most say pump pressure is 5-9psi. So, unless you have a regulator, I'd recommend a lower float level, around 3/8".
To speed the process of removing and installing the float for test purposes, I removed the little wire clip from the needle. Turns out, you don't need it. Just an extra part. Works fine without it and the needle ain't going anywhere so long as the float is installed.
The idle tubes were removed, the collars tapped back in place and then the tips soldered and drilled .031. I reinstalled the previous UIAB setscrews, which actually measured about .042.
The APT did have about .015" difference in the arms. I measured this using the depth side of my dial calipers. To do this, I stood the APT on the piston end on a steel plate. Then I put the caliper tail on top of the arm and measured down to the plate. Bent them until they were within a few thousandths using my crude method. For now, I've set the APT at 3.5 turns out and will lower a bit at a time until I get lean surge or off idle hesitation. Not today though...
What do you know, there is a screw on the 170 series choke pulloff. I applied vacuum to it and stuck a .140" drill bit between the front edge of the choke flap and airhorn. Then I turned the screw until the flap just contacted the bit. I still need to fine tune it in the morning when it is cold.
Reinstalled the carb and started the engine. Turned the idle mix screws in until the engine tried to die then backed out a half-turn. Let it warm up and then readjusted for verge of lean. Idle is smooth, very little engine vibration. At this point, I put a vacuum gauge on it and found this cam is pulling 19.5 in Hg!
Took it for a several mile cruise. No problems dying at the stop light. No run-on when I turn off the engine. Restart is instant, no having to fiddle with the pedal.
I'll fine tune the choke tomorrow morning when it is cold.
Plan to drive it like this for a few weeks to see how I like it.
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