Tuning The Q Jet

Performance Olds 307

Tuning The Q Jet

This page is under construction you are welcome to check it out, new articles will be added daily so check back. This Page is focused on adjusting the air fuel ratio of your Electronic Q Jet. If you are about to attemp to adjust your Q jet there are two things you first need to be sure of, first is too check the TPS sensor you can find an article on how to check and adjust this page Carburetor & Intakes 1 and second is to make sure your carb has had a rebuild somewere in its life because the adjustment screws are covered by "tamper free caps" that are usaly removed during a rebuild, if your has not been rebuilt and or the caps are still covering the adjustment screws then you should rebuild your Q JET carb first.

There are special tools that are needed to adjust your Q Jet, they cost just under $20 total. The tool to adjust the main metering of the M/C solenoid is J-28696-10, BT-7928, that is for part to full throttle mixture control of the primaries. Just above the red square in the picture to the right is the "Idle Air Bleed" adjustment screw, a simple flat head handles this task. 85 and later 307s Q jets do not have a M/C solenoid rich stop adjustment, on these carbs the M/C Solenoid lean stop handles both tasks. If the carb has never been rebuilt then it might still have the "Tamper free caps" inserted over the adjustment screws and may need to be removed but I dont suggest removing them unless you are going to rebuild the carb because drilling them out will leave junk in the carb.

The Idle mixture needles need tool # J-29030-B, BT-7610B. The Picture on the right show a carb with the caps still on this carb as you can see but that is the location of the idle mixture needles.

Adjusting The Engine Idle Speed (RPMs). The 307 likes to idle at about 600 in gear and 800 out of gear. I have fooled with these carbs for about 10 years now and this is the way I adjust the idle speed so that the idle speed is the same with the A/C on or off.

Basic understanding - There are two places to adjust when adjusting the idle speed, the first is the "base idle" this is the little spring loaded screw (on the base of the carb on the front drivers side just under the large vacume diapham called the ILC) that the throttle lever rest on. The other point of adjustment is the ILC (stands for "Idle Load Compensater") this is the vacume diapham on the front driverside of the carb that the throttle lever rest on. To make adjustements to this just grab the plungers base with a 1/2" wrench and turn the plungers tip with plyers.

FYI higher idle load from the A/C on will lower vacume and cause the spring inside the ILC to push the idle up alittle, thats the whole reason for the ILC is to keep idle consistant through idle loads. I adjust my idle speed by>>>

1. Taking the ILC off the carb but keeping the vacume line connected. Just set it aside for the next few steps. Then block the wheels and put the parking brake in, start the car and leave it in "N" for now. (The engine must be fully warm to make proper adjustments)

2. Then I adjust the idle (with the A/C off) at the idle set screw on the carb. This is the little spring loaded screw thats under the place the ILC mounts on the carb. the throttle lever rest on this at idle.

3. After I find a good idle speed in (600) and out (800) of gear then I put the ILC back on and adjust the ILC so that with the engine on at idle in 'N' and the A/C off the ILC's plunger is just resting firmly on the throttle lever but without actualy raising the idle off the idle set screw, then when I turn the A/C on the ILC should lift the idle off the idle set screw.
So basicly with the A/C off and engine on the idle should sit on the idle set screw at all times with the ILC's plunger as close to the throttle lever as possible without raising the idle off the idle set screw that way when the A/C is turned on the lose of vacume will cause the ILC to lift the idle off the idle set screw and hold the idle speed at the same RPMs. Hope thats understandable, If not let me know! Good Luck

Adjusting Idle Mixture,

Before doing this it is important that the tamper free caps have been removed from over the "idle mixture needles". Just so you know "IMN" is short for "idle mixture needles" and "AIB" is short for "air idle bleed" and thats how I put it to save typing space. The AIB is adjusted at the large flat head screw with the little hole in the center that it located on the very top of your carb just behind the "M/C solenoid rich adjustment stop" if you look at the image further up on this page you can see the large flat head screw with the little hole in the center just over the red square in that image. If your AIB is still being covered by the tamper free cap then you will need to remove that before adjusting the carb (I suggest a full rebuild if they are still in place because removing the caps will leave shavings in the carb that will need to be cleaned out). The IMN's are located on the bottom of the carb on the carbs base facing the front of the car, there are two IMN and both should away be adjusted equal, there is a image of them further up on this page, and them too will need to have the cap removed if they are not already. Now on to adjusting your idle mixture.

1. Start with the engine off, turning both IMN's all the way in (clockwise) then turning them both out (counter clockwise) 3 full turns, then start the car and place it into gear (A/C off) with the wheels blocked and parking brake on

2. Now go to the air idle bleed (for short - AIB) and turn it all the way in (clockwise) then turn it out (counter clockwise) to 2 turns out, then slowly (about 1 turn every 4 seconds ) turn the AIB out and pay attention to the idle looking for the best highest smoothest idle.

3. If you take the AIB past 5 turns you went to far, you want the AIB to be set between 4 and 5 turns when you are done so if the engine is happy with the AIB at 3 turns or less then you need to richen the IMN's by 1/2 (counter clockwise) and try step 2 again and keep doing so intill the AIB is happy at 4 to 5 turns out. Now if you find that the AIB wants 6 turns out with the IMN's set at 3 turns then you need to lean out the IMN's a 1/2 turn (clockwise) and try step 2 again, repeat intill the AIB is happy with 4 to 5 turns out. Basicly the more you turn the AIB out the leaner your idle is and the more you turn the IMN's out the richer you idle is. Its a balancing act, but when finished you should have a strong smooth idle. You may need to re adjust your idle speed after this!

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