technical details- 87 z28, stock q-jet carb, 305 v-8, recent tuneup, 700r4 tranny

background- rebuilt carburator everything came apart good and everything went back together well.

problem- after doing the carb rebuild i set it back to factory specs. being the dumb dumb i am i didnt copy down the turns each adjustment screw was at thinking i wouldnt have any issues. well when the engine is fresh from cold start it has gobs of power. very happy with that. but after the engine is warm the top end power drops sufficiently and also im getting terrible mileage. if im driving on the freeway after about 5-10 minutes the ses light comes on and the code is 45- o2 rich. if i adjust the mixture screws down the ses light doesnt come on but the top end suffers more and i dont gain any mileage. i checked my choke and it is working. i just cant think of anything else. can someone help me?

 

Does the carb make a clicking noise? Did you set the Dwell for the MCS?

 

E2se Carburetors

1. Remove the carburetor from the engine.
2. Remove the plugs covering the idle mixture needles.
3. Turn the mixture needle in until slightly seated, then back it out 4 turns.
4. If the plug in the air horn covering the idle air bleed has been removed, replace the air horn. If the plug is still in place, do not remove it.
5. Remove the vent stack screen assembly to gain access to the lean mixture screw.
6. Using tool J-28696-10 or equivalent, turn the lean mixture screw in until lightly seated, then back out 21/2 turns.
7. Install the carburetor on the engine.
8. Disconnect the bowl vent line at the carburetor.
9. Disconnect the EGR hose and canister purge hose at the carburetor. Cap the ports on the carburetor.
10. Find the hose from port D of the carburetor to the temperature sensor and secondary vacuum break thermal vacuum switch. Disconnect and plug the vacuum hose going to the air cleaner.
11. Connect the positive lead of a dwell meter to the mixture control solenoid test lead (green connector). Connect the other lead to ground. Set the meter to the 6 cylinder position.
12. Run the engine on the high step of the fast idle cam until the cooling fan starts to cycle.
13. Run the engine at 3,000 rpm and adjust the lean mixture screw slowly. Allow the reading to stabilize, obtain an average dwell of 35 degrees. It is normal for the dwell to vary in a narrow range.
14. Return to idle.
15. Adjust the idle mixture screw to obtain an average dwell of 25 degrees. Allow time for the reading to stabilize.
16. Run the engine at 3,000 rpm and note the dwell reading. It should be varying with an average reading of 35 degrees. If it does not, repeat the earlier steps.

E4mc Carburetor (Hot Air Choke)

1. Using tool J-29030-B, BT-7610-B, or equivalent, turn each idle mixture needle clockwise until lightly seated, then turn each mixture needle counterclockwise 3 turns.
2. Reinstall carburetor on engine, using a new flange mounting gasket, but do not install air cleaner or gasket at this time.
3. Disconnect vacuum hose to canister purge valve and plug it.
4. Connect the positive lead of a dwell meter to the mixture control solenoid test lead (green connector). Connect the other lead to ground. Set the meter to the 6 cylinder position.
5. Start engine and allow it to reach normal operating temperature.
6. While idling in D (N for manual transmission), adjust both mixture needles equally, in 1/8 turn increments, until dwell reading varies within the 25-35 degree range, attempting to be as close to 30 degrees as possible.
7. If reading is too low, turn mixture needles counterclockwise. If reading is too high, turn mixture needles clockwise. Allow time for dwell reading to stabilize after each adjustment.

After adjustments are complete, seal the idle mixture needle openings in the throttle body, using silicone sealant, RTV rubber, or equivalent. The sealer is required to discourage unnecessary readjustment of the setting and prevent fuel vapor loss in that area.

1. On vehicles without a carburetor-mounted Idle Load Compensator (ILC) , adjust curb idle speed if necessary.
2. Check, and if necessary, adjust fast idle speed, as described on the Vehicle Emission Control Information (VECI) label.

E4me Carburetors (Electric Choke)

1. Using tool J-29030, BT-7610-B, or equivalent, turn both idle mixture needles clockwise until they are lightly seated, then turn each mixture needle counterclockwise 3 turns.
2. Reinstall carburetor on engine using a new flange mounting gasket, but do not install air cleaner and gasket at this time.
3. Disconnect the vacuum hose to canister purge valve and plug it. Readjust the idle air bleed valve to finalize correct dwell reading.
4. Connect the positive lead of a dwell meter to the mixture control solenoid test lead (green connector). Connect the other lead to ground. Set the meter to the 6 cylinder position.
5. Start engine and run until fully warm, then repeat the idle air bleed valve adjustment.
6. If unable to set dwell to 25-35 degrees and the dwell is below 25 degrees, turn both mixture needles counterclockwise an additional turn. If dwell is above 35 degrees, turn both mixture needles clockwise an additional turn. Readjust idle air bleed valve to obtain dwell limits. Repeat as needed.
7. After adjustments are complete, seal the idle mixture needle openings in the throttle body, using silicone sealant, RTV rubber, or equivalent. The sealer is required to discourage unnecessary adjustment of the setting and to prevent fuel vapor loss in that area. Reconnect canister vacuum hose.
8. On vehicles without an Idle Load Compensator (ILC), adjust curb idle speed if necessary.
9. Check, and if necessary, adjust fast idle speed as described on Vehicle Emission Control Information (VECI) label.

 

yes it does. i didnt know i was supposed to set dwell on it. none of my directions said to do that.

 

ok. so at idle and part throttle im great. i have all my power back. but at cruising speeds of 40+ im getting a code 45, rich o2. sit in the drive way and im fine but sit in the idle and rev up to 2500 rpms sets the code off again. where should i start

 

adjust the TPS (search on TPS adjustment in carb forum).

 

Are you sure your back two barrels are working? Rev it with the breather off and check to make sure the vacuum is sucking the top two secondaries open, if not somethings whack insde your carb.