I just installed my original Quadrajet (7041205) on my 71 LS5. I was running a Holley prior. I had the Quadrajet rebuilt by Cliff Ruggles and this was my first chance I had to install it. I was able to get the car up and running. The idle was a little high so I had to adjust it down a little. When I took it out for a test drive the idle is too high (about 1500 RPM). I don't know a ton about carbs so i'll do the best to explain what's happening. It drives great through the gears but as soon as I start to slow down and down shift with the clutch in, the idle is about 1500 Rpm's. The only way to get it to drop it to tap the gas and it will drop down to 800 Rpm's. I'm not sure what causes this and how to get rid of it.

Thanks for any help..

 

is your choke hooked up? and what type of choke does it have? but really call Cliff he is a helpful guy very knowledgeable. you sound surprised you had to play with the idle, are you comfortable working on carburetors? or is it the quadrajet thing?

 

Yeah, the choke is hooked up. I don't mind messing with the carb a little bit but don't know a great deal about them. I was just lucky when I had Lars rebuild the Holley I had on the car. I threw it on and it ran great. I guess I was just a little spoiled. I dropped Cliff an email but thought I would ask the forum as well..

 

Cliff will take care of you. i have gotten stuff from him and he is a good guy. it sounds like your high idle cam is staying on high idle.i run a quick fuel double pumper but the choke isn't hooked up. don't need it in florida. good luck

 

Sounds like your choke is not disengaging fully. Probably needs some adjustment. The detailed procedure can be found in the Chevrolet Chassis Service Manual for your model year (fuel section...carb and choke adjustments).

There are diagrams involved, so you'll need to find a copy; words alone won't give you what you need.

 

After looking it over for a while this morning, I think I found something. It looks like the throttle doesn't return back to it's original position after pressing the gas petal. If I tap it a few time it will go back but it seems to get hung up if I don't. I'm not sure if the accelerator spring isn't strong enough to pull it all the way back or if the set up it self is just too tight. Is there anything I can do for that? I'm using the same spring as I have always had on the car.

Edit...

I tried this same thing with the engine NOT running and the throttle snaps back in the correct position against the idle screw...

I'll add a few pictures because everyone loves pictures... I wasn't sure if I was "maybe" missing a spring around the fast idle cam???

 

Is it correct to have only one throttle return spring on a '71 LS5?

I did a quick search and found this pair of springs for LS6. Just wondering if LS5 needs the two springs also.

http://www.ebay.com/itm/55-88-NOS-Ca...8bd47f&vxp=mtr

 

I'm not sure, I asked the rebuilder and he thought there was suppose to be double springs as well.

 

 

Is your choke linkage correct? Look at the choke stove and attaching arm. your arm differs and also appears bent. It may be a problem.

http://forums.corvetteforum.com/c3-g...-70-454-a.html

 

The choke linkage may be binding on the coil cover, but I don't think that's your problem. If the choke operates properly (the choke closes, and the engine drops off the high speed idle cam after it warms, and the pull-off functions), driving the car won't effect the choke. Look at the solenoid that pushes the throttle (a/c or anti-dieseling?) and make sure that isn't holding the throttle open when the engine is running.

 

If the carb is positioned a bit off-center, the throttle plates can rub/bind in the holes in the gasket. Loosen the carb retainer bolts and wiggle it around some to find the best place for it. Do the same with the gasket. Tighten the bolts and try it again.

 

A vacuum leak can also cause a high idle, returning to normal after blipping the throttle.

 

I think what I have come up with is the primary shaft is a bit tight. I lubed it up some and it seems to be loosing up. It's getting better so I figure that was the main issue. I did loosen up the bolts that hold down the carb and move the gasket around some and them retightened the bolts. So maybe the combination was the trick.

I will say that the Rochester doesn't seem to have the same top end snap as the Holley double pumper had. It may still need a little more tuning to get it perfect..

 

Matt -
You don't have a choke problem or a vacuum leak. Your choke is hooked up correctly, and your linkage is correct for a big block. I can see that your fast idle cam is fully dropped down, so your fast idle screw isn't touching the cam in that position. That's not the issue.

When Cliff builds a carb, he does a total disassembly (which you have to do in order to do the plating), including removal of the throttle plates from the shafts. When you re-assemble the t-plates to the shafts, it's easy to get one of the plates not exactly, perfectly aligned with the throttle plate bore. The throttle will operate fine in the static condition, but as soon as you apply a little manifold vacuum below the asymmetrical plates (the t-shafts are not on centerline on the plates: they are designed so that manifold vacuum will pull the plates closed), the throttle plates can stick a little in the bores, causing the exact condition you describe. The fix is to remove the throttle plate and loosed all 4 of the primary throttle plate screws, "tap-and-jar" the plates into better alignment in the bores, and then snug them back down. It only takes a very small movement to fix the issue, and I'd suggest you let Cliff do it for you, since it's easy to make the problem worse. The other issue is that shipping damage (not necessarily noticeable) can cause a slight bind, contributing to the issue. If Cliff is backlogged and can't do it right away, I'll be glad to take care of it for you at no cost other than return shipping - Cliff and I have known each other for many years, and I'll be happy to help out.

Glad to hear the Holley worked out well for you - I can test your Q-Jet to assure the same level of bolt-on performance, too. I believe Cliff also tests the carbs like I do, so I can maintain the integrity of his work and tuning: Cliff, Henry and I all set the Q-Jets up the same way, and we all have the same philosophy on the tuning parameters. Of the three of us, Cliff is certainly the top-end guy with the actual restoration work he does on the plating and finishes, so there should be no issue getting the inconsistent idle rectified.

Lars

 

Interesting comment-I thought the same about my Holley 4175 when I switched to it years ago from the Qjet although most folks say there is no performance difference.

 

That's awesome Lars.. I think your right on with that. Cliff did have to take the whole thing down to replate which is the only reason I didn't send it to you.. I'll see how it feels the next time I get a chance drive the car around.. I'll check in with Cliff to see what his back log is if I need it. If it's too long that is amazing you would help me out with that. I certainly don't want to do it myself.

Lars.. Should the Quadrajet perform just as well as the Holley 4613 double pumper you built for me? The throttle response is the same but when you really got into the Holley it felt like it through you back in the seat. The Rochester response is right on but doesn't seem to have the extra.. It almost feels like the Holley has another 50 HP or something..

 

I've done quite a bit of dyno testing, comparing Holleys, Q-Jets and other carbs. As long as you compare Q-Jets and Holleys of comparable cfm, the top-end power of the two carbs is virtually identical, if both carbs are correctly tuned and set up.

That being said, "seat-of-the-pants" feel is a very poor way to judge actual performance. In a car as heavy as a Vette, you cannot tell "by feel" any performance change under 20 horsepower. The Holley and the Q-Jet will run within about 5 hp of each other on the top end.

However, the Q-Jet will make significantly more torque and power than the Holley below 4000 rpm - by about 35 hp. Above 4000, the Holley DP really comes on, so you tend to get an "artificial" sensation that the Holley is running stronger on the top end. The Q-Jet, if it's properly set up, is actually running the same, but it pulls stronger on the bottom end, making the higher-rpm transition less noticeable.

Lars

 

Nice Explanation Lars. Thanks.

 

Matt -
Don't tell people I build Holleys... you're going to ruin my reputation.


...and, by the way, where the heck is Gordon (Commander_47) in this conversation, anyway..?? Commando never takes this long to sniff out a good Q-Jet versus Holley conversation. Gordo - are you out there??

Lars