455 olds quadrajet

4speedracer · 02-10-2014, 01:39 AM

Working on car not a race car, with lean idle condition and unable to get low enough idle speed approx. 900rpm .Question i have is did some quadrajets have holes drilled in primary throttle plates from factory ? Have vacuum advance hooked to manifold vacuum, without manifold vac engine labors to much and shows late timing with vac gauge. Base timing at 8 degrees, also has no vacuum leaks found .
Thanks Jamie

Dave Noll · 02-10-2014, 02:22 AM

Possible plugged idle circuit.Quite common on a Q-jet. If you just mist the choke tower with carb clean does idle pick up ? (carefully)

Ed Wright · 02-10-2014, 08:28 AM

It's been a few years, but I used to rebuild at least one Quadrajets a day. I don't remember seeing primary throttle blades drilled from the factory. It's getting air from somewhere to idle at 900 RPM. Has to be a vacuum leak, throttle blade has moved so they don't seat, or holes somebody drilled. A stock engine should idle at 8 deg BTDC, of course vacuum will be higher with more spark advance. As mentioned before, try spraying something like Berryman's B12 in the top of the carb. If it's lean the idle will pick up. If not too lean, it won't like that stuff. It will like it just better than not near enough fuel. Normally, 2 1/2 turns out is close to where the idle mixture screws end up.
Most of the time, if the carb is too lean with no vacuum leaks, you will only find one side with something in the idle fuel restriction. Turning the mixture screw on that side will have very little effect.
Good luck!

Tom Meyer · 02-10-2014, 08:45 AM

I am sure you checked but make sure the secondarys are not open a little bit .Tom

Ed Wright · 02-10-2014, 11:05 AM

Quote:

Originally Posted by Tom Meyer

I am sure you checked but make sure the secondarys are not open a little bit .Tom

I had forgotten about that. Been close to 20 years since I worked on one. I made a little hook tool that I used, I put another half wrap on the spring on the secondary shaft. I also tweaked the link on the driver's side to push the secondaries shut when the primaries closed. Most had a good bit of slack there. When the shaft bores in the base wore enough they didn't always close tight, I drilled the shaft bores out and installed brass bushings. A place in Kansas sold the bushings and tooling to do it.

R. Thorne · 02-10-2014, 04:13 PM

If idle mixture screw circuits are indeed the problem, a quick fix is to take them out and spray some carb cleaner in (with the straw that comes with most cans), then a quick shot of compressed air through the holes.

02-10-2014, 01:39 AM	#1
4speedracer Junior Member Join Date: Sep 2011 Posts: 51 Likes: 0 Liked 10 Times in 6 Posts	455 olds quadrajet Working on car not a race car, with lean idle condition and unable to get low enough idle speed approx. 900rpm .Question i have is did some quadrajets have holes drilled in primary throttle plates from factory ? Have vacuum advance hooked to manifold vacuum, without manifold vac engine labors to much and shows late timing with vac gauge. Base timing at 8 degrees, also has no vacuum leaks found . Thanks Jamie

02-10-2014, 02:22 AM	#2
Dave Noll Senior Member Join Date: Nov 2007 Location: Div. 6, Eastern, WA Posts: 709 Likes: 2,671 Liked 238 Times in 111 Posts	Re: 455 olds quadrajet Possible plugged idle circuit.Quite common on a Q-jet. If you just mist the choke tower with carb clean does idle pick up ? (carefully) __________________ Dave Noll, EF/S ,?/SA 6526

02-10-2014, 08:28 AM	#3
Ed Wright Veteran Member Join Date: Mar 2005 Location: Sand Springs, OK Posts: 8,132 Likes: 896 Liked 390 Times in 170 Posts	Re: 455 olds quadrajet It's been a few years, but I used to rebuild at least one Quadrajets a day. I don't remember seeing primary throttle blades drilled from the factory. It's getting air from somewhere to idle at 900 RPM. Has to be a vacuum leak, throttle blade has moved so they don't seat, or holes somebody drilled. A stock engine should idle at 8 deg BTDC, of course vacuum will be higher with more spark advance. As mentioned before, try spraying something like Berryman's B12 in the top of the carb. If it's lean the idle will pick up. If not too lean, it won't like that stuff. It will like it just better than not near enough fuel. Normally, 2 1/2 turns out is close to where the idle mixture screws end up. Most of the time, if the carb is too lean with no vacuum leaks, you will only find one side with something in the idle fuel restriction. Turning the mixture screw on that side will have very little effect. Good luck! __________________ Ed Wright 4156 SS/JA

02-10-2014, 08:45 AM	#4
Tom Meyer Senior Member Join Date: Aug 2003 Location: Pierce NE Posts: 936 Likes: 78 Liked 354 Times in 120 Posts	Re: 455 olds quadrajet I am sure you checked but make sure the secondarys are not open a little bit .Tom __________________ Tom Meyer 5240 SS Stock ???

02-10-2014, 04:13 PM	#6
R. Thorne Member Join Date: May 2009 Posts: 182 Likes: 62 Liked 100 Times in 33 Posts	Re: 455 olds quadrajet If idle mixture screw circuits are indeed the problem, a quick fix is to take them out and spray some carb cleaner in (with the straw that comes with most cans), then a quick shot of compressed air through the holes.