Tim Burgess

Just rebuilt the carb for an '87 LG4 & the O2 sensor shows rich always & I get a code 45 from that. The mixture control (MC) solenoid is new & makes a clicking sound when the ign is turned on, so it is functioning - is one of the two MC sol adjustments out of wack? There's one that is adjusted from the top of the air horn & one that sets the height of the MC sol that can be adjusted if the air horn is removed - I set them to the same number of turns down as they were when I took the carb apart. Any ideas as to what to check?

Tim Burgess

Was able to fix the rich condition @ idle by cranking in the idle mixture screws from the factory spec of 3-3/8 turns out to 1 turn out. Guess those factory setup specs aren't cast in concrete - unless something else on the carb is still out of proper adjustment. The O2 crossing count now increments rapidly @ idle, but incrementing slows considerably @ part throttle - with the O2 sensor reading mostly rich.....how do I lean out the part throttle mixture a bit?? My guess is that the M/C solenoid height needs to be decreased....any other ideas??? I think the factory M/C sol height spec is like 1.3" from the top of the primary metering rod seat.

99Hawk120

I'll give this a shot, let me summarize the problem:

Originally it was rich at idle. Turning the screws in fixed this.
It's rich at part throttle.

Have you checked the MC dwell (or duty cycle) at curb idle (in gear for an auto) and high idle (~2000 RPM)?

Because you're getting a code 45, I'm going to assume the computer is correcting for a perceived rich condition. The dwell should be fixed over 50* (70%+ duty cycle) in this case.

Adjusting the idle screws in made the O2 better. Okay, that tends to tell me the feedback portion of the computer system is working fine.

1 turn in seems WAY to little. My 84 won't even run with less than 3 turns, and my Oldsmobile (3.8L V6) wants about three to run "right"--at 1 it adds a lot of fuel to compensate.

Did the exhaust smell rich before adjusting the idle screws? Does it still smell rich at part throttle?

If the answer is yes, then unmetered fuel must be getting in somewhere. I bet I can tell you what your problem is. I bet the float bowl plugs on the bottom of your Qjet are leaking. Did you cover them with epoxy (JB weld is my tool of choice) when you did the rebuild?

I had that problem when I first put the Qjet on the olds, it smelled rich as stink and woulnd't idle below 1500 (it would flood out if you closed the throttle blades more).

As far as the MC solenoid height, I know the travel is supposed to be 4/32". I've always done it by setting the lean stop with the air horn off with a special tool, and then setting the rich stop to adjust the total travel. FYI, the MC adjustment doesn't have as much effect on the mixture as you would think.

Tim Burgess

Thanks for the info. Code 45 did not occur after the idle screw adjustment & the MC sol duty cycle was in the 70's on the Autoxray, @ idle, if I recall correctly. Can the plugs be glued inside the float bowl - access by removing only the air horn - or do they have to be glued from the bottom of the main body?

99Hawk120

Mid 70's eh. On my camaro 75% is a FULL LEAN command. On my Olds it's 80%. Either way, the computer is pulling out the maximum amount of fuel the system will allow. I'm almost certain you've got the dreaded leaky float bowl plugs, because that's EXACTLY what happened to my Olds. Unfortunately, they have to be glued from underneath.

You can do this by removing the carb from the car. Unscrew the back two screws behind the secondaries (the reall long ones). Flip the carb over and unscrew the 3 remaining screws that hold the throttle body on. Pull the throttle body off.

You should see five plugs. Two large ones that are vertical and right next to each other. I believe the other 3 are "angled". They should be pretty obvious. Cover them all with epoxy.

Don't try to test for leaks simply by filling the carb with gas while off the car. It's been my experience that the plugs don't normally "leak" without engine vacuum pulling on them.

Wait for the epoxy to dry and reinstall the throttle body. For piece of mind, turn the carb over and remove the air horn and make sure nothing has moved inside (when I did mine, nothing had, AND i'd had to shake it while it was upside down, too). The only things that could really move involve the float system and the primary mixture rods.

Reinstall on the car after resetting the idle screws to three turns out.

Tim Burgess

Thanks for all the info - I very much appreciate it! Will glue those plugs.....

Tim Burgess

Gluing the plugs fixed the problem - the M/C is now running in the 50% range - thanks for the help!

I also discovered a new problem - and one solution - & was wondering if anyone else ran into this. When the car was cold, it would not run very well under load - it idled OK, but coughed & sputtered when driven, until it warmed up, at which point it would run fine. The problem was exaggerated in very cold weather. The choke and thermostatic air cleaner were functioning as they should. I had installed a set of intake gaskets with the EGR blockoff plates & I thought that the absense of the exhaust heat under the carb necessary for EFE was causing the cold run problem. I removed the gaskets & replaced them with the stock type that allowed the hot exhaust gas to flow under the carb & that fixed the cold run problem. Anyone else experience this problem or have a different solution that would allow the exhaust gas blockoff plates to remain in place?