Hi all, I'm new to the board, I hang out a lot around NastyZ28.com, but now that my cousin picked up a third gen T/A, I need some help. The carburetor stumbles and hesitates sometimes. It's like the carb is getting no air, or fuel,when you get into the throttle a little. It's an '86 TA, with the carburated 305 motor. Anyone else had this problem? How would I go about fixing it? I'm thinking it could be caused by the fact that the car has no exhaust after the y pipe. If the o2 sensor thinks the exhaust is rich/lean, it will adjust the carb accordingly, right?
Moderator
Right when you first roll into the throttle? Check the accelerator pump first.
If you're engine is stumbling during idle (rough idle).... and everything as far as timing and vacuum checks out okay, you have a leaky accelerator pump (the little pump on top of the CARB that get's pressed down when the throttle lever is pulled back.... the accelerator pump can be accessed by removing the air horn)....
If you're engine stumbles ONLY when you're driving (when there's a load), it is DEFINITELY you're secondary plate..... its opening way too soon!
If you're engine stumbles ONLY when you're driving (when there's a load), it is DEFINITELY you're secondary plate..... its opening way too soon!
The idle is fine, but i'd still like to check the accelerator pump. How would I check the pump? How would I adjust the secondary plate to open later?
Firstly.... you need a torx screw driver, try to find one with multiple bit's, as the two center screws are a different size than all the outer ones (you'll see what I mean when you take off the air horn)....
1) Remove the air horn (top of the CARB) by removing all of the torx screws. You'll have to disconnect the mechanical arm coming from the vacuum for the secondary... to fully remove the air horn. Remove the old gasket(s), and remove the accelerator pump. Replace the accelerator pump, and gasket(s), and install by doing everything in reverse....
2) After you installed the arm for the secondary plate, you'll notice there is a very small screw facing you from the side of the CARB (look between the top of the arm, where it meets the linkage to open the secondary plate). After you find this screw.... DON'T try to turn it just yet (it's locked). There is another screw, a tiny torx screw (yeah.... GM made SURE you brought these back for tune-up's lol), UNDERNEATH the mechanical arm (it's ON the top left side of the air horn, but underneath). What you want to do, to make life a lot easier down the road..... remove that tiny torx screw, and with a hacksaw....cut a 'slit' into it, converting it to a flat screw type (I say this because if you use the torx screwdriver enough.... that little screw will warp and strip, especially from the engine heat if you're tuning while the car is running. Plus this should be done while you have the air horn off when replacing the accelerator pump). Loosen the torx screw just enough that the screw facing you can move, then turn the screw facing you CLOCKWISE (tighter). Turn the screw facing you 1/4 of a turn, then while you're holding the screw facing you (in place), TIGHTEN the torx screw underneath (basically.... the torx screw underneath acts like a clamp for the screw facing you, and once the screw facing you is adjusted to when you want it to open the secondary plate, the tightened torx screw underneath holds it firmly in place). Keep doing the above until the hesitation goes away....
1) Remove the air horn (top of the CARB) by removing all of the torx screws. You'll have to disconnect the mechanical arm coming from the vacuum for the secondary... to fully remove the air horn. Remove the old gasket(s), and remove the accelerator pump. Replace the accelerator pump, and gasket(s), and install by doing everything in reverse....
2) After you installed the arm for the secondary plate, you'll notice there is a very small screw facing you from the side of the CARB (look between the top of the arm, where it meets the linkage to open the secondary plate). After you find this screw.... DON'T try to turn it just yet (it's locked). There is another screw, a tiny torx screw (yeah.... GM made SURE you brought these back for tune-up's lol), UNDERNEATH the mechanical arm (it's ON the top left side of the air horn, but underneath). What you want to do, to make life a lot easier down the road..... remove that tiny torx screw, and with a hacksaw....cut a 'slit' into it, converting it to a flat screw type (I say this because if you use the torx screwdriver enough.... that little screw will warp and strip, especially from the engine heat if you're tuning while the car is running. Plus this should be done while you have the air horn off when replacing the accelerator pump). Loosen the torx screw just enough that the screw facing you can move, then turn the screw facing you CLOCKWISE (tighter). Turn the screw facing you 1/4 of a turn, then while you're holding the screw facing you (in place), TIGHTEN the torx screw underneath (basically.... the torx screw underneath acts like a clamp for the screw facing you, and once the screw facing you is adjusted to when you want it to open the secondary plate, the tightened torx screw underneath holds it firmly in place). Keep doing the above until the hesitation goes away....
When installing the air horn back on the CARB, before you do this, REMOVE the metering rods and hanger. Install them back on AFTER the air horn is back on.... otherwise, if you try to do it all in one shot, you might damage the rods, and tear your new gasket.
Thanks Street Lethal, all that info's gonna help a lot. Carburetors are really the only things that still baffle me about engine work. Set timing, new intake, new heads, rebuild the motor,sure. But ask me something about the carb, and I go running for a book.
Junior Member
SecondGenZ,
There's a good techbook put out by Haynes titled "Rochester Carburetor Manual" which is very good. It describes the Q-Jet in detail and how to rebuild it and also gives several carburetor related symptoms and possible solutions. You can find it at pretty well any parts store.
Jory
There's a good techbook put out by Haynes titled "Rochester Carburetor Manual" which is very good. It describes the Q-Jet in detail and how to rebuild it and also gives several carburetor related symptoms and possible solutions. You can find it at pretty well any parts store.
Jory