I've got a rebuilt QJ from Advance - a number of applications including 69 396, and 350hp 350 (vette) on my machine shop 330 hp 350 with Edelbrock Performer intake. I noticed the secondary air valve is sticking about 1/3 open when I open it manually. I need to apply some amount of force to get it passed that point, after which it opens all the way, then it sticks on the way back closed. I have yet to see it open while I'm running the engine. I know it stays closed under high vacuum so it won't open at idle, but it doesn't budge when revving the engine or anything. Makes me wonder if it's opening at all, which would at least partially explain the crappy performance I'm getting (it seems to fall on it's face when the secondaries kick in). I stopped by Advance to get them to order a new one, since it's still under warranty but before I lug my old one over does it sound defective to you guys? I'd hate to look like a moron while at the same time wasting everyone's time. Thanks again for the help guys

Andy

Did you loosen the little-bitty hold-down screw thats on the pass. side end of the top butterfly's shaft?

Then you need to use a little-bitty Allen Wrench stuck in the end of the shaft to set the tension on the butterfly's return spring!

It doesn't take much and be carefull that you don't pop it off it's location b/c then you will have to start over again!!

AND fwiw, the top butterfly's HAVE to be set, ran, then adjusted AND ran each timer b/c running w/o a load on it WON'T really kick them in properly!

In other words the motor needs to be under running conditions to set the top butterfly's right! IMHO!!!

I have mine on my old 406 where they would not kick in until like almost 70 mph on the highway in forth gear, but around town, I could floor it in second gear at 30 mph and they dropped right in NO BOG at all!

It took me part of a Sat. afternoon testing and a tuning to get them this way back then...

pdq67

try spraying some WD-40 in the shaft bushings (3 places) and into the area where the return spring rides on the peg sticking out of the shaft. this is the same area pdq67 was mentioning. if you use a small mirror, look up at the passenger side end of the the air valve shaft from the bottom, you'll see where this little spring is. Occasionally that spring doesn't slide right, usually a little WD fixes it. Also, sometimes the link that goes to the choke pull-off gets in a bind where it attaches into the curved slot in the little plate swedged onto the passenger side of the air valve shaft. Either the link or the plate can be bent. Also, you can check the senter of the shaft where the plastic cam lifts the secondary metering rod hanger as the air valve opens, make sure there's no problems there. I've seen the cams partially melted from a carb fire and suchlike. Remember, these carbs are rebuilt be people in a factory, most of them have never seen a carb installed on an engine in their life. Sometimes real obvious (to us) stuff is missed. Might want to check if the secondary metering rods are the same, I've seen several rebuilts with random jets and rods. Advance are usually better than that, though.

It's also possible that the airhorn (the carb's top section) is warped, or the secondary air valve plates are scraping. The only thing that you could try in this case would be to loosen the screws holding down the plates and see if moving the plates slightly allows the shaft to turn more easily. (Be warned - these screws are peened on the bottom, they will break if you try to loosen them without filing of the peening.) If the airhorn is warped the only cure is to straighten it, or remachine the secondary air valve bore that the shaft turns in.

Having said that, if you bought this carb recently I would get a different one. You can fix this one, but it's going to be tricky. Why fool around if you paid good money for a "rebuilt" carb?

Mike

Andy,you have posted mult issues here in T/C with that cookie cutter rblt q-jet from the get go and your spinning your wheels trying to get it fixed on your own when you dont seen to have the experience to do it which is ok,we all have to start somewhere.

But,you cant expect an advanced auto rblt q-jet meant to cover many applications of stock motors with 200hp to work correctly on your 330 hp motor,just isnt going to happen. That's why i gave you the info for a good fuel calibration setup for the q-jet to start with for your motor setup including all the pt#'s for jets,rods,power piston spring etc . When these q-jets are rblt at some assembly line buisness you have no way of knowing what fuel calibration meaning jets/rods/power piston spring etc are in that carb . That carb is likely setup for the late 70's early 80's when the motors were weak with very mild cams & 160-200hp and your trying get the same calibration to work on a perf 330hp motor with 50% more power which is a big mismatch to begin with.

You have posted here in T/C a very rich idle situation going on which i and many others have tryed to help you with. As we told you before the rich problem shows issues with float lvl,wrong fuel calibration like jets,prim metering rods,wrong power piston spring for the cam your running ,too high of fuel presure,and now the latest issues is a sticking upper secondary air valve and your chasing your tail with all these issues and not knowing what to do with them.

The only way to get your rich idle fixed you posted the other day along with this latest issue of the sticking upper secondary valve is you have to pull that carb appart to check the float and float level,ensure the the correct jets,rods(prim & secondary),and power piston spring are in primary side of the carb for your specific motor setup and fix the now sticking sec upper valve at the same time too.

If you dont have the experience to confidently pull that q-jet appart and get it fixed you need to take it to a local carb person that does or send it to sean murphy induction in CA to get it fixed. Sean runs the carbs on a motor to chk them out before they leave his shop to ensure they are working correctly and he is an honest person to deal with too,look up his website to check his services out.

So either get a good q-jet rbld book/video and dig into it or send it out to Sean or you will continue to spin your wheels and cause many of us here to spend a lot of time trying to help you out when you seem reluctant to pull the carb appart which is what needs to be done.

Good luck.

Scott

Scott I appreciate the help you and others have been giving me while I puzzle this out. I AM trying to get it to run better but at the same time I'm also learning about how the QJ is put together and how it works. This is the first QuadraJet I have had and all this fumbling around is all part of the learning process for me. It would certainly be easier to send it out to someone for a going over but I've never been a black-box type person - I'm at least trying to learn a little about these things so I'm not completely in the dark. I probably will end up sending it out to have it optimized for my particular engine combo, because like you said those out of the box carbs are built for many different applications and logically it would make sense that they are optimized for none of them. As I learn more about the QJ I'm realizing they are a very complex thing and there are many subtleties that can be changed to make performance better, but will also make performance worse if you don't know what you're doing. I could easily end up spending a lot more time spinning my wheels (a lot more than I already have, I would say) when I should be out driving around with the top down.


Please don't think I am ignoring anyone's advice. Every little bit of information is very welcomed and I very much appreciate the patience you and everyone else has shown while I ask my silly and seemingly disjointed questions.

Cheers,
Andy

Andy,

Good advice above. On paper it looks as though the QJ you bought should be a pretty close match to the the 350 you have.

As was pointed out these rebuilt, budget minded, units are probably not subject to the strictest quality control measures so you really don't know what's in it (rods, jets, springs) unless you disassemble it. I don't think it would be a stretch to say that the listed application means that the unit will actually bolt on and accept the choke, fuel line, vacuum lines and such. Probable has less to do with correct calibration. Again, won't know unless you open it.

Try to free up the air valve like was said. If the secondaries are adjusted correctly you actually should be able to get the air valve to crack open a little sitting in your driveway.

If I understand these things right from studying my own QJ (all too often) all fuel for the primary side goes through the primary jets (accept for the acc pump), but the primary rods, jets, or the power piston spring don't actually have anything to do with the idle circuit. You could remove the jets and rods altogether and it will still idle (can't remove the power piston because doing so would cause a vac leak). The idle circuit is metered by the air bleeds and the adjustment screws.

As long as you have the primary throttle blades closed almost completely - ensuring the engine isn't pulling fuel from the transfer slots, that your timing and idle speed is appropirate, that you have no vacuum leaks, and that the carb isn't leaking fuel from the boosters (easy to check by letting the engine idle and looking down the primary side of the carb with a flashlight) the only other cause of a rich idle would be the idle circuit air bleeds are too small for the cam you are using.

Even with my mild-ish solid lifter cam mine runs rich at idle. I just don't have the itty-bitty drill bits to open up the bleeds.

Dan

Andy69,

I didn't realize that the carb you were having problems described in the other thread was a NEW parts store rebuild. In that case, keep taking it back until you get one that runs right, IMHO. That Lars paper I linked to you SHOULD have something in there about what he thinks about those carbs- sometimes they can be pretty bad, other times, they aren't that bad BUT aren't usually as good as decent core to rebuild/rejet/etc. yourself.

If you go to www.corvettefaq.com, not only will you find the link I posted for you, but you will also find Lars's Qjet Rebuild paper. Download all that Lars stuff and read through it. Its at LEAST as good as the Doug Roe book, IMHO. He also has jetting/rods spreadsheets on there.

I know the deal with those parts store carbs. I had one on my car quite a while ago, and it leaked from the airhorn gasket, bogged, had parts from 3 different carbs (IMHO), it just was not great. I had basically totally written off Qjets until a cool guy here at TC a few posts up helped me out with one I had actually found in a shed. With his help, and a few parts, it runs great! Some starting woes made it pretty hard at first until I pulled my head out of the sand and realized that it was an ignition problem I CREATED, because the carb pumped out gas everytime I hit the pedal.

This isn't to say that my car is a daily driver- far from it, but I was running a Holley Spreadbore, and the FIRST AND ONLY Qjet I rebuilt was WORLDS better than the parts store carb, and a little better overall than the spreadbore Holley, which I do still like.

If it was a nice core, I'd be all for sending it to a tuner, but a parts store carb? Why not just take it back and order one from SUmmit? They say in the catalog that they are all bench tested BEFORE they hit the warehouse. They are $290 though.

I read through the stuff you sent, Buzz. Very good info. I'm still trying to wrap my mind around the complexity of this carb. It looks like there are a zillion things that can be out of whack. I guess I just assumed I would bypass all these problems by just buying a brand new carb and that it would would be set up correctly. Well, that's part of the process I guess. I think Lars did say he thought Advance carbs were better than most, but that none of them were best. Part of this flailing around is I'm trying to figure out if I really want to get into opening the carb or just call Sean Murphy or Summit and be done with it. I also want to be sure that what I am seeing is actually the carb and not something else.

Thanks again for the help, guys.

Cheers,
Andy

Have you rebuilt a Holley, Andy? IF you have, a Qjet is really not that hard- REALLY. Its reputation really overshadows the fact that its NOT that difficult when you have stuff like that Lars info. Here is another link for you:

http://www.tocmp.com/manuals/Carbs/Rochester/QJet/index.htm


I am nowhere near as adept at building Qjets like Uncle PennyBags or others who have posted here, but I took a shot and rebuilt mine and it runs great. I DID have a starting problem which I thought was the Qjet, but finally figured out (from help here of course :) ) I had my starter R wire and resistor wire wired together and then attached to the ballast resistor I should have never been using :p .

There are more linkages, etc. on a Qjet, but the bright side to that is ONCE you get it set, its set. You just have to be very methodical with taking it apart and going through it, and TAKE YOUR TIME- thats the key, IMHO.

I rebuilt a Holley years ago when I was like 19 and it still ran like crap afterwards, but that was before the internet and the fine folks here at Team Chevelle :) . I also spent a lot of time messing with a Rochester 4-Jet (4GC, I think?), which worked pretty well on my otherwise stock 1973 350. The Quadrajet seems to have a lot more odd looking parts than the 4-Jet :confused: but I like to think I'm at least halfways smart enough to figure it out. Hmmm maybe I can tackle this...

Andy

OK here's an update. I took another look at the air valve and it's definitely restricted in its travel. I wanted to just return it for a refund but since it has been almost a year they said I'll have to settle for warranty replacement. That's OK.

I called up Sean Murphy Induction and had a chat (he doesn't say much...), and I'm going to pick up one of their Stage II Quadrajets. I figure as much as I'd like to play around with it I want my car on the road more, plus the new one will have an integrated electric choke instead of that fussy divorced choke. Besides I have other projects I have to attend to (wifey want's a privacy fence and a brick patio, and the house painted. I figure those should buy me at LEAST 6 months of car projects without getting the Evil Eye and the "you spent HOW MUCH??" comments :) ).

I'm going to hang on to the parts store carb then when I get a chance I can take it apart and start looking at how they're put together. That way I won't be in a rush to get it back together and on the car.

Thanks for all the help and links.

Cheers,
Andy