Quadrajet carb adjustment question

1964CutlassSC · September 10th, 2009, 01:56 PM

Ok so my good friend has a 69 442 convert (400ci). He had the ignition upgraded to electronic ignition (not MSD or anything fancy) this year and had a rebuilt Quadrajet installed. No matter how much we play with the adjustment screws on the fuel/air mixture, the motor never seems to try to choke out like I expect it to. The car seems to run rich most of the time and to me, the car doesn't have as much snap as it should. With the old carb and points, the car used to really run rich too. They said the problem was a cracked fuel bowl on the old carb. The shop that put the carb on says they put the right one on and everything is set correctly (timing, etc.) but how can we tell if the carb and jets are correct?

Does anyone have an instruction sheet on the right way to adjust the Quadrajet or maybe can provide things to check? There are no vacuum leaks that we know of.

I appreciate any advice you can provide!

mugzilla · September 10th, 2009, 02:46 PM

Take some wd40 and spray around different parts of the carb like the basegasket etc. to see if you have a vacuum leak. If you have a leak you can shut off the idle air adjustment and it won't "choke out" ...

Erinyes · September 10th, 2009, 02:48 PM

This sounds like one of those cases where you might have multiple problems...

I'd start with the basics: Check compression, timing (initial and total), plugs, wires, vacuum hose routing (make sure it's ported vacuum to distributor, as well as other hoses), PCV system, and check for manifold leaks (simple job - let the engine idle, spray along the intake gaskets with carb spray - but have a fire extinguisher handy!). All that is just to rule out potential problems, not that I really think there is a serious risk of trouble.

Once you've definitively narrowed it down to the carb, there are a host of variables involved. "They say" it is the right carb, but is it? Check the numbers. I found a site the other day that details the numbering scheme on Q-Jets, but it's on my home computer that I won't see for two more days.

If it is not the right carb, any one or more of the following could be inappropriate for that engine/trans/rear end combo: float level, power spring, primary jets, primary rods, secondary rods, secondary hangers, secondary spring tension, total air flow, and possibly something else I'm not remembering after being out of the business for 20 years.

Assuming it's the right carb, your best bet is to find a copy of Doug Roe's QJet book, tear the carb down, and rebuild it yourself to ensure that all the internal specs are correct.

Afterwards, if there is still a chronic rich condition, I would start fine tuning the carb with different jets, rods and power spring - one change at a time!
Never make multiple changes when tweaking the guts of a carb. Make one alteration, then test it. Use a vacuum gauge, stopwatch, pull the plugs to see how they were affected... be scientific, or you'll never really know what has actually happened.

The site I found has various jets and rods available, which surprised me. He also has throttle bushing kits.

1964CutlassSC · September 10th, 2009, 02:51 PM

Quote:

Originally Posted by mugzilla

Take some wd40 and spray around different parts of the carb like the basegasket etc. to see if you have a vacuum leak. If you have a leak you can shut off the idle air adjustment and it won't "choke out" ...

What will occur when we spray the WD40?

1964CutlassSC · September 10th, 2009, 02:53 PM

Thanks Erinyes..

If you track that link down when you get back to your home PC, if you could pass it along, that would be great. I found a few links online before I posted but it got pretty complicated and I wanted to talk to you all here first to see where you recommended starting over from.

Erinyes · September 10th, 2009, 03:00 PM

I'll do that.

When you spray to find find leaks, if there is a vacuum leak it pulls the fluid into the engine; it will change the idle in direct ratio to the extent of the leak. I don't really expect a leak, though - if there is a strong vacuum leak, you'd be running lean at idle. I'd still check, just to rule it out. I've seen vehicles with horrendous vacuum leaks that also had carbs leaking horribly, and they more or less canceled each other out. Fix the leak, and it wouldn't run until the carb was rebuilt.

66ninetyeightls · September 10th, 2009, 04:53 PM

http://www.carburetor.ca/carbs/tech/...jet-index.html

This website has all the codes as well as the manuals.

Erinyes · September 11th, 2009, 08:39 PM

Here's the site I was thinking of:

http://www.cliffshighperformance.com

Let us know what happens. I'm curious to see what the problem actually is...

1964f-85 · September 14th, 2009, 10:00 AM

if you reboilt the carbs, pull out the metering rods. If not inserted corretly during the rebuild the tips can get bent, not allowing them to seat in the jets and causing a rich condition.

svnt442 · September 14th, 2009, 03:14 PM

Quote:

Originally Posted by 1964CutlassSC

Ok so my good friend has a 69 442 convert (400ci). He had the ignition upgraded to electronic ignition (not MSD or anything fancy)

What Dist? If it's a stock HEI from another car then you need to alter the initial timing to 20° @ 1100RPM. The 8° or 10° will not cut it because there is a different amount of mechanical advance built into the factory HEI.

September 10th, 2009, 01:56 PM	#1 (permalink)
1964CutlassSC Registered User Join Date: Jul 2009 Location: Keswick, Ontario, Canada Posts: 81	Quadrajet carb adjustment question Ok so my good friend has a 69 442 convert (400ci). He had the ignition upgraded to electronic ignition (not MSD or anything fancy) this year and had a rebuilt Quadrajet installed. No matter how much we play with the adjustment screws on the fuel/air mixture, the motor never seems to try to choke out like I expect it to. The car seems to run rich most of the time and to me, the car doesn't have as much snap as it should. With the old carb and points, the car used to really run rich too. They said the problem was a cracked fuel bowl on the old carb. The shop that put the carb on says they put the right one on and everything is set correctly (timing, etc.) but how can we tell if the carb and jets are correct? Does anyone have an instruction sheet on the right way to adjust the Quadrajet or maybe can provide things to check? There are no vacuum leaks that we know of. I appreciate any advice you can provide!

September 14th, 2009, 10:00 AM	#9 (permalink)
1964f-85 Registered User Join Date: Mar 2008 Posts: 74	if you reboilt the carbs, pull out the metering rods. If not inserted corretly during the rebuild the tips can get bent, not allowing them to seat in the jets and causing a rich condition. __________________ My 64 F-85 455, 4sp, 3:25's

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September 10th, 2009, 02:46 PM	#2 (permalink)
mugzilla is Fast Enough ... Join Date: Jul 2008 Location: dogtown Posts: 848	Take some wd40 and spray around different parts of the carb like the basegasket etc. to see if you have a vacuum leak. If you have a leak you can shut off the idle air adjustment and it won't "choke out" ...

September 10th, 2009, 02:48 PM	#3 (permalink)
Erinyes Registered User Join Date: Aug 2009 Posts: 29	This sounds like one of those cases where you might have multiple problems... I'd start with the basics: Check compression, timing (initial and total), plugs, wires, vacuum hose routing (make sure it's ported vacuum to distributor, as well as other hoses), PCV system, and check for manifold leaks (simple job - let the engine idle, spray along the intake gaskets with carb spray - but have a fire extinguisher handy!). All that is just to rule out potential problems, not that I really think there is a serious risk of trouble. Once you've definitively narrowed it down to the carb, there are a host of variables involved. "They say" it is the right carb, but is it? Check the numbers. I found a site the other day that details the numbering scheme on Q-Jets, but it's on my home computer that I won't see for two more days. If it is not the right carb, any one or more of the following could be inappropriate for that engine/trans/rear end combo: float level, power spring, primary jets, primary rods, secondary rods, secondary hangers, secondary spring tension, total air flow, and possibly something else I'm not remembering after being out of the business for 20 years. Assuming it's the right carb, your best bet is to find a copy of Doug Roe's QJet book, tear the carb down, and rebuild it yourself to ensure that all the internal specs are correct. Afterwards, if there is still a chronic rich condition, I would start fine tuning the carb with different jets, rods and power spring - one change at a time! Never make multiple changes when tweaking the guts of a carb. Make one alteration, then test it. Use a vacuum gauge, stopwatch, pull the plugs to see how they were affected... be scientific, or you'll never really know what has actually happened. The site I found has various jets and rods available, which surprised me. He also has throttle bushing kits.

September 10th, 2009, 02:53 PM	#5 (permalink)
1964CutlassSC Registered User Join Date: Jul 2009 Location: Keswick, Ontario, Canada Posts: 81	Thanks Erinyes.. If you track that link down when you get back to your home PC, if you could pass it along, that would be great. I found a few links online before I posted but it got pretty complicated and I wanted to talk to you all here first to see where you recommended starting over from.

September 10th, 2009, 03:00 PM	#6 (permalink)
Erinyes Registered User Join Date: Aug 2009 Posts: 29	I'll do that. When you spray to find find leaks, if there is a vacuum leak it pulls the fluid into the engine; it will change the idle in direct ratio to the extent of the leak. I don't really expect a leak, though - if there is a strong vacuum leak, you'd be running lean at idle. I'd still check, just to rule it out. I've seen vehicles with horrendous vacuum leaks that also had carbs leaking horribly, and they more or less canceled each other out. Fix the leak, and it wouldn't run until the carb was rebuilt.

September 10th, 2009, 04:53 PM	#7 (permalink)
66ninetyeightls Registered User Join Date: Aug 2009 Location: Burlington, Ontario Posts: 166	http://www.carburetor.ca/carbs/tech/...jet-index.html This website has all the codes as well as the manuals.

September 11th, 2009, 08:39 PM	#8 (permalink)
Erinyes Registered User Join Date: Aug 2009 Posts: 29	Here's the site I was thinking of: http://www.cliffshighperformance.com Let us know what happens. I'm curious to see what the problem actually is...