Let me start by saying that yes I know that it would be easier to "get the right carb" but my finances aren't able to support that right now.

So, I have a feedback carburator with out the computer on a 350. Headers, small cam, Torker II intake, MSD 6. My problem started about a year or so ago. I hit WOT, and the revs climb, the engine starts to miss heavily at upper rpms. I thought that it was the wires so I replaced them. Same problem. Then I replaced the plugs. Then the cap & rotor. Then the Coil. My ignition is all new, and I still have this problem. So I thought it could be a vaccum leak since I need to use a carb adapter for the Q-jet to mount on the Torker II. I sprayed carb cleaner all around the base and no change in idle. So I go out for a test drive to see exactly when it happens. If I open the secondaries (pedal to the metal!) it really gets up and goes. Then when I get up there, it starts missing. I took out my tach cause someone broke into my car and tried to steal it so I don't know what the rpms are. But if I take my foot out of it just a bit, It stops. But the power isn't there. And if I put it back in, it happens again. I don't drive this car everyday, just once a week, but when I do, I love the power, until it starts missing.
So, my question is this: I know that I need specalized equipment to start messing with the carb, (other than idle speed and mixture), but what happens if it was already out of adjustment. Could that cause this problem? How (in my back yard with no special equipment) could I get it adusted well enough to get my acceleration back? I have a Harbor Freight infered thermometer, if that helps. I have a home made tool that fits the other two adjustment screws.

 

I cant quite figure out what car you're talking about, what engine, and what engine it came with. Is it a car that came with the computer quadrajet system and you put in a 350 replacing the 305, keeping the same carb?

I'd tell you that you really should have a voltmeter to check your tps and a dwell meter to check your mcs, but since this problem is only after it goes wide open and has been there for a while, your idle mixture's not going to have much to do with it anyway. I almost want to guess that maybe your secondary rods arent right for your engine, like its starving for fuel and having a lean misfire.

Also are you sure your distributor is advanced properly?

 

If you've got the computer controlled carb but the computer is not connected, it's never going to run 'right'.

Aside from that, issues at higher RPMs are NOT the result of vacuum leaks or idle mixture settings. That's kinda a law.

If it's missing under load that's indicative of a weak ignition system. You've replaced everything except the distributor? A weak pickup coil could cause your problems OR a completely wore out distributor. Check the shaft play on the dist. If it wobbles there's not much you can do to save it.

Of course if this is the original small-cap dist then the computer isn't controlling the timing advance anymore and you're running on the base timing of the Ignition Control Module, essentially a 'limp home' feature.

If you're at all interested in getting decent throttle response and much improved mileage you'll need to swap the carb AND the distributor for mechanical units. I wouldn't invest any $ in either now that should be used for replacements.

 

Ok, let me go a little further. The motor was built for my '82 T/A. So it had to be smog legal. It came from a '77 Impala. Same with the 350THM. I pulled the computer out of the T/A. And then later changed to the vaccum advance dist. still using the CC carb. I wanted it to be correct, (pull the CC quad and run the other one) so I took the non CC quad, rebuilt it and installed it. It really didn't run well. So I went back to the original CC quad. It ran really good for a couple of years.
The MSD is connected straight to the distributor's magnetic pickup. The ignition module has been removed. The coil is an Accel unit. It's not too old. I've tried other coils too.
The missing only happens at high rpms with full throttle. Anything more than like 80% throttle. When I back off just enough, it stops. But I don't have the top end power like before. It used to pull reallly good. Even up to 7000rpms with this carb. Nothing has changed, except the missing. Since I've replaced all of the ignition, (except the dist. which I've checked and is in good condition) All I can think of is the carb needs to be adjusted. And I understand that at high rpms the idle mixture won't change that, that's why I'm not talking about the idle mixture screws. There are three other adjustment screws that "your not supposed to touch". Maybe they need to be adjusted like I said in my original post. And I understand that it won't work perfect, I'm not worried about that, but that's why I tried to replace the CC with the non CC originally. I just want it to run like before with the same set up.

 

Is it 'missing', as in mis-firing, which is your ignition or just running out of steam? Does it miss and sputter or just stop running then pick back up when the throttle is pulled back?

 

It's missing and sputtering. That's why I first went after the ignition. It seemed as if the wires were bad. The headers that I had on it before would melt the boot for #6 or #4 I can't remember right now. It would miss, but at all rpms. I've since changed the headers. But it doesn't feel like when it gets to a certain rpm then it starts to miss, but when the throttle is all the way down. I've checked the butterflies and they are at a 90* angle when WOT. It feels like a lean condition, but this carb should go full rich when the computer isn't connected. The soloniod for the main metering jets isn't energized so it pulls out the jets, right? But like I said, this only happens during WOT, not part throttle. And not just when the secondaries are opened, but when they are all the way open. What about the secondary choke? I haven't adjusted the tension screw. Could it be too loose? Would that cause a problem at WOT and not say 80% throttle? If I hit it hard, and the miss starts, I'll let off and get some more power, and the rpms climb, but slower than if there was no miss at WOT.

 

A weak ignition system is more likely to cause problems when cylinder pressures are higher and more energy is required to ignite the charge. Try a spark tester to see how strong your spark is. The pickup coil is maybe the only part you haven't replaced?

 

When you say the "pick up coil" are you talking about the magnetic sensor in the distributor that the MSD is connected to? How could that be weak, and still working? I was under the impression that it either worked or it didn't. Essentially, it is just a trigger for the MSD. I can't see how that would cause the problem. I understand that with higher combustion presure, the more spark is needed, but like I said, it only happens when the throttle is all the way open. Cause, like I said, when I let off the throttle just a little bit, then the problem stops, but the rpms still climb. So if it was the magnetic trigger being weak, then as the rpms go up, the more the miss would happen.

 

Sounds like a carburetor problem to me, in the secondaries (lean miss, most likely). Once you've confirmed ignition base, mechanical, and vacuum timing are working properly, obtain a carb gasket kit, tear it down and blow out all passages with compressed air then slap it back together. Or, buy an unmolested mechanical Q-Jet off EBAY or fleamarket and rebuild it. These are great carbs when matched to the application and properly tuned. Incidentally, on the old CCC Q-Jets, the computer didn't have any control over the secondaries, only primary mixture control. With your current configuration, you could probably take out the CCCQ-jet primary control parts (solenoid, solenoid plunger, and primary jet needles, but not the airhorn valve) and not even notice any difference (the part throttle would still run too rich). Not a lecture, just facts: The problem with running a CCC Q-jet without the computer is the part-throttle primary mixture will never be correct(always too rich). Using the two baseplate mixture screw needles, you can probably get the idle mixture dialed in. Too much fuel will cause your exhaust to run hot and could overheat/melt your cat converter ceramic elements, restricting the exhaust. I'm surprised it passes California emissions, but who am I to argue? By the way, Not that it matters at WOT(no vacuum) but there isn't really a good vacuum port on the CCC carb for distributor vacuum advance, although the EGR port on the passenger front corner should get you close. Good luck!

 

Its hard to know based on the info we have but I have seen cars misfire when they are not getting enough fuel. At WOT it is possible that it is not getting enough fuel or starving for fuel as someone mentioned.

Kevin