Need some advice with a Q-jet
09-28-2002, 09:22 PM
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Need some advice with a Q-jet
The Caprice has a real bad bog when you punch it, but only when it's warmed up, when the engine is cold, it runs like a raped ape. absolutely wonderful.
I tightened the air door, and that helped a little, but not enough.
It bogs for about 1.5 seconds when it's floored from any speed. If you punch it fast enough, it will almost (and sometimes does) stall.
Shifts are also extremely slow, not nearly quick enough for a 700 at WOT. Adjusting the TV cable has little effect other than shift points.
Any ideas?
The carb is a 1985 stock LG4 Q-jet (only mod is the air door adjustment), the engine is a basically stock smog 350. 76cc, 1.94/1.50, flat-tops. "summit" cam, whatever the hell that is..
LO3 manifolds, stock LG4 intake.
Running about 8* advanced base timing, which should be perfectly acceptable, and damn near dead-on, for this combo, I'd assume.
Could use some advice.
I tightened the air door, and that helped a little, but not enough.
It bogs for about 1.5 seconds when it's floored from any speed. If you punch it fast enough, it will almost (and sometimes does) stall.
Shifts are also extremely slow, not nearly quick enough for a 700 at WOT. Adjusting the TV cable has little effect other than shift points.
Any ideas?
The carb is a 1985 stock LG4 Q-jet (only mod is the air door adjustment), the engine is a basically stock smog 350. 76cc, 1.94/1.50, flat-tops. "summit" cam, whatever the hell that is..
LO3 manifolds, stock LG4 intake.
Running about 8* advanced base timing, which should be perfectly acceptable, and damn near dead-on, for this combo, I'd assume.
Could use some advice.
09-28-2002, 10:36 PM
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Sounds like the carb is giving the engine more gas than it can handle. When the engine is cold, the secondaries are locked out and you only run on the primaries. You noted an improvement when you tightened the air door for the secondaries which delays their opening, so you're on the right track.
Now as for your timing, if it's not computer controlled you can run 10-12 degrees with no problem. Have you checked to see if your vacuum advance can is working properly? does it leak? Is it actually moving the advance assembly inside the distributor? Has anyone changed the weights and springs of the distributor advance? If someone put in lighter springs, you'll have way too much advance way too soon. You don't want max advance until 2400rpm.
If you have a timing light, you can do this in the driveway. Set the initial timing and while the vacuum advance is still disconnected, gradually speed up the engine and use the timing light to see at what rpm the advance stops increasing. You should get another 12-14 degrees between idle and 2400 rpm. If all 12-14 degrees are 'in' before that, you need a stiffer spring. You can get a weight and spring kit at a speed shop. If you're not getting 12-14 degrees, you may have to play with the weights, filing and shaping them until you do get 12-14 degrees of mechanical advance. Once you get the mechanical advance settled, reconnect the vaccum advance. I did this to an older Corvette a few years ago the the results were amazing.
I'd start with the distributor/timing first then move to the carburetor. Good luck
Now as for your timing, if it's not computer controlled you can run 10-12 degrees with no problem. Have you checked to see if your vacuum advance can is working properly? does it leak? Is it actually moving the advance assembly inside the distributor? Has anyone changed the weights and springs of the distributor advance? If someone put in lighter springs, you'll have way too much advance way too soon. You don't want max advance until 2400rpm.
If you have a timing light, you can do this in the driveway. Set the initial timing and while the vacuum advance is still disconnected, gradually speed up the engine and use the timing light to see at what rpm the advance stops increasing. You should get another 12-14 degrees between idle and 2400 rpm. If all 12-14 degrees are 'in' before that, you need a stiffer spring. You can get a weight and spring kit at a speed shop. If you're not getting 12-14 degrees, you may have to play with the weights, filing and shaping them until you do get 12-14 degrees of mechanical advance. Once you get the mechanical advance settled, reconnect the vaccum advance. I did this to an older Corvette a few years ago the the results were amazing.
I'd start with the distributor/timing first then move to the carburetor. Good luck
10-01-2002, 12:59 AM
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So, it's totally computer controlled? No vacuum advance, weights or springs? If so, you're stuck with whatever the computer's programmed for, which takes you back to the carburetor. Keep tweaking that air door. Is the carb a computer controlled model, too? Have you rebuilt it? You also have about a mile of vacuum hoses running around your engine bay. Ever checked those for cracks or leaks? The car is 17 years old and if that's never been done, who knows what the problem could be. A lot of those hoses are bypassed when the car is cold then begin to operate as the car warms up. Also, there's the charcoal canister that may be trashed after only 17 years of service. I had an 84 Citation X-11 and at the five year point developed a heavy ping and knock. Finally, I went through all the hoses and the problem went away. Some of them fell apart in my hand.
You have a really heavy car and it's never going to launch like a Camaro. But it could run a lot better. It's got a **** converter and probably 2.56:1 rear gears. Maybe a rear from a Monte Carlo SS would fit in there!
You have a really heavy car and it's never going to launch like a Camaro. But it could run a lot better. It's got a **** converter and probably 2.56:1 rear gears. Maybe a rear from a Monte Carlo SS would fit in there!
10-01-2002, 10:10 AM
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I have two vaccum hoses on the whole car, choke pull-off and brake booster. Forgot one, the hose for the fuel return..
Yes it's a CCQJet.
<img src="http://www.nethirdgen.org/mac/87caprice/caprice03.jpg">
Yes it's a CCQJet.
<img src="http://www.nethirdgen.org/mac/87caprice/caprice03.jpg">
10-02-2002, 01:36 AM
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Dude, yer making it hard for me to figure out this problem! Were there supposed to be more hoses and you don't have them? Let me go back to a more basic question. Did the car just start doing this or has it been doing it all along?
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