Slant Six Forum :: 71 Duster w/ 225 & Holley 1920 problems

Quote:

I'm no carb expert.
This may help, I thought the "old car" method was to open up the butterflies, back out mixture screw until you get max rpm's, then turn it back in 1/4 turn.

Don't know whether you mean choke or throttle when you say "butterflies", but idle mixture is never set with the throttle anywhere but closed, and if you have to go and open the choke, the engine's not warm enough to set the idle mixture.

There is no magical number of turns that is too rich, too lean, or just right for any kind of carburetor. Each and every carburetor needs a different adjustment; that's why the adjusting screw is there. There's also nothing such as an idle adjustment that's correct in the driveway but not on the road. Either the adjustment is correct or it isn't. Proceed per the Holley 1920 operation and repair manual (pdf).

Author:	shoncook [ Thu Dec 11, 2008 9:17 am ]
Post subject:	71 Duster w/ 225 & Holley 1920 problems
I figured I'd come straight to the source of the best help. My 71 Duster is coming along. It runs well, except a few really annoying problems. The carb, the Holley 1920, was giving me trouble, so I rebuilt it with a kit from NAPA. The part number they gave me and I ordered based on numbers on the carb matches the part number listed on this site, so I figure I'm safe there. The problem is that the car dies after traveling at speed and coming to a stop. At speed, push in the clutch and brake and the car dies. It will start immediately after, and you can even get it started by popping the clutch if you are still rolling. The car runs really well besides this (and one other small annoyance below), accelerating with no hesitation and whatnot. Could this be poor setting of the float? Bowl vent? I'm lost. Another problem is that while the car idles smooth at fast idle, when that kicks off the idle can be a little rough at times. I should mention that I only set the mixture screw by the old "old car" method of going all the way in, then back off 1.5 turns from there. Something I picked up from my dad, I guess. I pulled the plugs last night, just to make sure that wasn't causing the rough idle, and they look fine. I wire brushed them and put them back in and it ran the same. Thanks for any help, folks.

Author:	stonethk [ Thu Dec 11, 2008 9:56 am ]
Post subject:
I'm no carb expert. This may help, I thought the "old car" method was to open up the butterflies, back out mixture screw until you get max rpm's, then turn it back in 1/4 turn. I think the way you did it was to get a "baseline" setting.

Author:	Aggressive Ted [ Thu Dec 11, 2008 10:00 am ]
Post subject:
shoncook, 1.5 turns is too lean for these one barrel carbs. It may work in the drive way but not while driving. It is fine on a four barrel, but with a one barrel your idling too lean. Any idea what size main jet you have installed? My 1920 is set at 2.5 turns and runs great. Hopefully you are running the stock MOPAR PCV. If not, and your running a GM unit, yo will need to richen the idle mixture even more, maybe 2 and 3/4 turns out. The GM PCV units will pull a little more air out of the crankcase and cause the carb to lean out at idle. Richen the idle mixture screw up a little and let us know how it goes....

Author:	shoncook [ Thu Dec 11, 2008 10:32 am ]
Post subject:
Thanks for the help guys. I'll take a screwdriver with me after work and see what I can make happen. Do you think running rich might cause my stalling, or would this just help my idle issues?

Author:	Aggressive Ted [ Thu Dec 11, 2008 10:37 am ]
Post subject:
No, running lean will cause stalling. Running rich will make it load up to the point where it would be running rough, but it will still run unless the plugs get fouled, and you can smell the difference at the tail pipe. At 1.5 turns you will not be running rich. As long as you have a good ignition system/coil/good spark the plugs will run tan even at 4 turns out. Reference: I see 10 volts at the coil @ 750 rpm.

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71 Duster w/ 225 & Holley 1920 problems https://slantsix.org/forum/viewtopic.php?t=32727	Page 1 of 1

Author:	shoncook [ Thu Dec 11, 2008 10:49 am ]
Post subject:
Gah, sorry, totally mistyped that. I meant lean.

Author:	SlantSixDan [ Thu Dec 11, 2008 11:26 am ]
Post subject:
Quote: I'm no carb expert. This may help, I thought the "old car" method was to open up the butterflies, back out mixture screw until you get max rpm's, then turn it back in 1/4 turn. Don't know whether you mean choke or throttle when you say "butterflies", but idle mixture is never set with the throttle anywhere but closed, and if you have to go and open the choke, the engine's not warm enough to set the idle mixture. There is no magical number of turns that is too rich, too lean, or just right for any kind of carburetor. Each and every carburetor needs a different adjustment; that's why the adjusting screw is there. There's also nothing such as an idle adjustment that's correct in the driveway but not on the road. Either the adjustment is correct or it isn't. Proceed per the Holley 1920 operation and repair manual (pdf).

Author:	stonethk [ Thu Dec 11, 2008 11:29 am ]
Post subject:
DOH!

Author:	shoncook [ Thu Dec 11, 2008 11:56 am ]
Post subject:
Quote: Quote: I'm no carb expert. This may help, I thought the "old car" method was to open up the butterflies, back out mixture screw until you get max rpm's, then turn it back in 1/4 turn. Don't know whether you mean choke or throttle when you say "butterflies", but idle mixture is never set with the throttle anywhere but closed, and if you have to go and open the choke, the engine's not warm enough to set the idle mixture. There is no magical number of turns that is too rich, too lean, or just right for any kind of carburetor. Each and every carburetor needs a different adjustment; that's why the adjusting screw is there. There's also nothing such as an idle adjustment that's correct in the driveway but not on the road. Either the adjustment is correct or it isn't. Proceed per the Holley 1920 operation and repair manual (pdf). Wow, could have used this these last couple nights. Thanks Dan, must not have seen that around.

Author:	wjajr [ Thu Dec 11, 2008 12:15 pm ]
Post subject:
A Holley video on adjusting idle mixture. The instructions work for one, two, or four barrels. http://www.holleytv.com/featured_landing.php?reset=true

Author:	shoncook [ Wed Dec 17, 2008 12:45 pm ]
Post subject:
Folks, I'm still having a heck of a time getting this thing running well. I pulled the carb off and reset the float according to that guide Dan posted. No difference there. I've tried all three positions on the pump cam linkage, with no difference there. I'm beginning to think that I screwed up the rebuild somehow. To me it smells to be running too rich, but adjusting that screw doesn't seem to do me much good, and I unfortunately do not have a vacuum meter to check with. Could this be indicative of too much gas being dumped somewhere? Part of me suspects that "Hot Idle Compensator." That gasket was all buggered up before the rebuild. Covering what I thought was the hot idle inlet port in the horn just killed the engine, though, which didn't smooth out idle... I'm getting a hair frustrated. That always seems to happen when carbs get involved though!

Author:	SlantSixDan [ Wed Dec 17, 2008 1:37 pm ]
Post subject:
Well, you know what I would suggest!

Author:	Aggressive Ted [ Thu Dec 18, 2008 12:29 pm ]
Post subject:
See if you can make a new gasket to keep the compensator from leaking vacuum.

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