Got a few problems with the otherwise problem-free Quadrajet.

Thought I'd throw out the specs on the motor first.

010 350 with flat-tops
416 heads (yes, on 87 octane...LOTS of timing retard)
Non-CC Q-jet
Performer Intake
comp XE 256
Hooker longtubes


Firstly, the carb was rebuilt a few months back by a shop and has had one problem since then. The AV flaps will NOT open on their own when the motor is running. I assume this is probably tension being too high, but the flaps just drop when you put your finger on them, and don't appear to have any tension.

To remedy this, I've had the AV flaps wired open. With them closed (and nothing going through the secondaries), the motor would choke itself at about 3000 rpms and wouldn't wind past. Since I've wired them open, it pulls all the way through it's powerband fine.

My only problem right now is a bog. Now, the jetting and rods on this carb aren't anything special and are probably the stock ones for a mild motor from the 70s/80s. Don't know if that will help you or not.

But, it only bogs if the car is sitting still and you punch it off the line. If you stall it up and punch it, it spins well into second, as it should. If you roll the car to maybe 3 or 5 mph and punch it, same result (it's a one-legger, traction doesn't exist). It's only when you punch it off the line. And it only bogs for a second, once the bog stops it pulls hard again.

I initially tried giving it more fuel via the mixture screws. It didn't solve the problem, but it did give it some more top-end pull. I tried giving it a little less fuel and it didn't seem to help either.

I've tried adjusting ignition timing as well, and no results there either.

The motor winds up in nuetral fine and has awesome throttle response. It sucks in air hard enough that it pulls down on the foam on my triangle aircleaner. If you're on gravel and punch it, it's fine. It's just when it gets out on the pavement.

I imagine this all has to do with the AV flaps being non-functional, but I'm wondering if the carb needs some tweaking (rods, jets, better accel pump, etc.) to work well with this setup. I did some searching, but thought I'd put up a post to get an opinion on it.

Also, the choke doesn't adjust itself, and hasn't since the rebuilt. I have the primary choke plates forced open at all times, otherwise it runs way too rich, which would suggest that I need to lean out the motor via the mixture.

 

First off, what makes you think the secondary flaps don't open? Just flooring the throttle while the car is sitting in your driveway won't be enough to open the top flaps. Those will open when the vacuum drops, which happens when the car is under heavy load. By hard wiring the flaps open means you have the secondary rods fully open all the time, therefore as soon as the bottom secondaries open your not getting good metering.

Try returning the top flaps to normal, and try changing the seconday metering rods to a thinner rod. The stock units weren't made to make that much power on a <200HP motor of the 80s. The secondary rods will have an ID Code stamping on them. You can look at this chart https://www.thirdgen.org/newdesign/tech/rods.shtml to see which one you have, and maybe get a few sets with longer/thinner tips.

 

The reason I had the flaps wired open was because it felt like the secondaries just weren't getting any air. I unwired them, and they seem to work sometimes, and sometimes not. I've spent some time messing with timing and mixture, and I've almost got the bog eliminated. The only thing it does now is bog at WOT regardless of when or how it's floored. It's fine up to about 80% throttle, but when you put it all the way to the floor it just bogs and stumbles.

 

I'm reading myself in circles reading your post, so if I give you a garbled answer, i'll try again:

your secondary air flaps 'flop' open when you push down on them, right? ok, do you know how to adjust the tension in it? if so, tension it up, until they have a bit of spring to it. Basically until you can push on the back tip of them to open them, with your pinky, and they will snap shut. If they rotate slowly (back closing), they might be gummed up, try carb cleaner or something.

if your choke doesn't pull itself off on it's own, you probably want to fix it, rather then work around it (kinda a pain...)
when the car is running, is there voltage at the choke electrical plug? Assuming yes, you may just need to replace the choke thermostat, not expensive.

you've got a similar motor to what i'm building, 010 350, flat tops, 416 heads, non-cc qjet... cool. Runs well?

oh yea, do you know what primary rods and jets are in the car, and secondary rods ?

PS. 2.14 gears in the rear? good *** that must be sleepy... with a 700R4? You must be able to cruise at 100MPH at 1200RPM or something, boy

 

Okay, this may seem dumb, but I'm learning about these carbs quickly.

I don't know what's missing, but the hangar is not linked to the AV flaps. If you drop the flaps, the hangar doesn't move up like it should, it stays in the same place (a K hangar, BTW). Wouldn't this just starve the motor? Isn't the hangar supposed to come up to raise the rods out of the jets?

 

Gobs of torque and throttle response, seems to be good so far for a budget build (I got the 416 heads for $40). I'm in bad need of a posi (and better gears), though. It would be nice if I could put her to the floor without a bog though, .

The gears are pretty horrible. If your cruising around town and mash it in 3rd, the tach needle basically doesn't move at all as the mph go up. Even with the stupid 14" stock wheels and small tires, if I take it to 6000 rpms in 1st I'm doing 60, and this with the first gear of a 700. Gears and posi are definitely next on the list .

 

yea, as you push the secondary flaps open, the hanger should be pushed up, maybe 1/4" or so. If you remove the hanger, and push open your air flaps, you should see a 'cam' type of thingie, rotate, and push up on where the hanger was....
not sure what would be causing that. Got a digital camera? Can you take a pic?

 

I looked, and apparently the guy rebuilt it without the cam lobe in there!

Any idea on where I can get just a cam lobe? Will a rebuilt kit include it? Can I buy it separate? Is it going to have to be a JY find?

Also, I looked at a buddy's BBC Q-jet's cam yesterday, and noticed it has a parts number stamped on it. Do they sell multiple/different cam lobes for that, perhaps for tuning? If so, any one I should look for in particular?

 

that would definately be a JY item. You might be able to just snag (5 finger discount) that one part, but you're probably better off buying the entire carb (one very similar to yours), for spare parts.

Not sure about the P/N on the cam, your hanger choice will probably do the same thing as a slightly different shaped cam.

 

http://www.carburetion.com/quadrajet.asp

P/N 85-104.

 

Thanks for the help guys. I think I may be able to kill this bog. Will update the thread on how she runs after getting the cam lobe in there.

 

geez, essentially running with the secondary rods plugged, no secondary flow at all... That musta been a bit of dog.

Thx 57, I guess you can buy anything online. Too bad they don't have post '75, pre-cc q-jet rods.. Oh well, edelbrock's still there for that.

 

Got the cam along with a set of DH rods and an O hangar from a JY find. Performance is obviously more substantial with the newly usable secondaries.

However, I do have a high RPM bog/stumble that only happens when the motor winds itself up past about 4500 rpms. The AV flaps are at zero tension, so I'm thinking maybe better rods hangar, or perhaps fuel pump?

Only one fuel pump on this car (stock mechanical on the block), and a new fuel filter on the line, will check the in-carb one again tomorrow.

I'll make a short film while driving the car at WOT to give the best illustration and post it later...

 

I'm not familiar with dh rods, or the O hanger... Perhaps check on the guide on the main page I think, to see where DH stacks up.

? I've heard people say zero tension, and to me that sounds like a bad thing, so your secondaries should bog that way. Give them the proper tension (5 second mod) and try it that way.

Other then that, a lean and rich bog feel similar, so you'd have to find out which it is, before you go changing things. One thing to do is disconnect your acc pump, if better, it was rich, if worse, it was lean....
click here:
https://webdisk.ucalgary.ca/~jmknopp/public_html/
and download the 3 q-jet tuning papers. Lots of reading, but one part tells you how to optimally set up your q-jet, from primary rods and jets, to secondaries. I think it'd be worth your while to tune your carb just right for your semi oddball combo.
oh right, the gist of that is that those articles also give VERY good, totally un-ambiguous ways to identify and tune out a bog, give'r torque!

 

I'll definitely check out the site.

As far as the zero tension thing, I was goin by the tech article on here. I had thought the concept was to set it at zero tension, and keep trying richer rods until the bog was gone. With the way this particular bog is, I don't know if the AV flaps really have anything to do with it, because it's not related to throttle response.

Most of the time it will pull all the way through in first well, and then to about 4500 rpms or more in second, and then it will start lurching, where it will bog slightly and then pull and then bog again fairly rapidly. Sometimes it does it in first as well, but it's usually a bit later in first (like at 5000 rpms or more). I've never tested it in 3rd, as my tires just aren't speed rated quite that high .

Tomorrow I'll break out the digital video camera for it, that's best way to illustrate it.

 

Two things work together to prevent bog:
- Initially, the choke pull-off.
- After vacuum drops, the AV tension takes over.

You need both. You can't adjust the AV tension properly without the pull-off (unless you are very, very astute with q-jets and know what else to modify). The pull-off may do the job by itself with zero AV tension, but most likely it will not.