Stereotypical idle issues

I have a 1986 mazda b2000 LX standard everything. i have upgraded the exhaust (headers, o2 sensor delete because i dont have to worry about emissions, cat delete, and a magnaflow exhaust), carburetor (32/36 weber that my father and i tuned for HOURS to get it right), a full egr delete, and had everything timed, the ignition coil, plugs, and wires all replaced. i have 2 issues, 1. when turning off the engine sometimes it sputters for a second THEN dies, and 2. idles high even though i have turned down the idle as much as possible. the idle doesnt start high. when i start the truck i give it a little throttle (im talking a pube hair) and it goes down to approximately the 1000 rpm mark (i have put in a tach) but slowly raises itself to the 1250 (ish) mark and does not move.

im wondering if it is the "dashpot" that i have seen a few things about, and if its something thats commonly bad in brand new weber carbs. is the dashpot something that can be adjusted to help? Another thing i was thinking was my distributor might be old and worn. the last is that there was a small wire (approx. 20 gauge) connected to the distributor that has fallen off, its connector to the ignition coil with a plastic "relay" that no mechanic friends of mine have any real clue about.

I am still new with cars so if you could speak to me like im an idiot (within reason) that would be completely helpful, and possibly funny.

First of all your idle is set too high. It should be set at 850 rpm at idle, so maybe you can start there. Have you checked to make sure there is a little bit of slack in the cable so that the carb plate can close fully?

You might also check for a vacuum leak between the intake manifold and the head, and also between the base of the carb and the intake manifold. You can use a can of either with a pinpoint nozzle and spray it at the seam where the intake manifold connects to the head while the engine is running, and the base of the carb to see if your idle quality changes. You may have a vacuum leak where the carb attaches to the intake manifold. You can at least eliminate a vacuum leak as a possibility by doing this step.

If you aren't experiencing surging or misfires under acceleration or at idle, I don't think the distributor is a problem.

If you could post a picture of what you refer to as a "relay" that might help with your diagnoses. Relays usually have at least three wires attached to them and so maybe what you are referring to is a noise filter for the radio.

The stock carburetors use an idle stop solenoid which opens when you turn off the key, to super lean out the idle mixture and cause the engine to starve for fuel. Without that, maybe you will have to leave your truck in gear while idling, hold the brake and release the clutch.

What kind of gas mileage do you get?

Approx. 19 mpg or 12.3 L/100km

my idle is set as low as it will go. No backfires (except what i was told should be expected) until i turn off the engine, and then it will stutter and die out within 5 seconds and it feels like there is slack in the cable, but not a large amount.

Have you tried turning in the mixture screw to cut back on the idle fuel supply? That would cause the idle speed to drop some 19mpg is low and I think you should be getting better fuel mileage than that. I know the mechanical carbs don't get as good mileage as the electronic carbs do (I got 24 with my bone stock b2200 extended cab) but I think you getting less than 22 means you are running rich or something. How far do you have the mixture screw turned out from stop? I think Cusser on this board has a Weber. Maybe he will have some ideas if he reads this thread. Without being in front of your truck, I still think maybe that your cable is holding the carb plate partially open, and maybe you need more slack. If you use a flash light and look down into the carburetor, the carb plate should be fully closed at idle. The cable should be sloppy loose. You will never notice it under operation. Something is preventing you from getting an idle below 1000 rpm.

I've had my '88 B2200 Cab Plus 5-speed since 1994. I had issues with intermittent stalling (dangerous), added Redline Weber 32/36 DGEV kit and distributor ignitor and pickup in Dec. 2005 to fix that (a mechanic diagnosed stock carb being the culprit, and after carb install he discovered the distributor issue, possibly he was wrong about the stock carb then). Of course, back then I didn't know that one should check or sand flat the adapter plates for the Weber, now I know.

The B2200 runs good, no running issues there. Now for mpg: I do have a cross-bed tool box, carry like 100 lbs in there, and being in Arizona, the AC gets used most of the year. Anyway, my own B2200 never got better than 19-20 mpg with the stock carburetor, and same 19-20 mpg after installing the Weber. That said: I do like the Weber, and chances are high that if my stock carb was not bad in 2005, that it would've gone south soon after. I just don't worry about the mileage on the B2200 (my 1998 and 2004 4-cylinder, 5-speed Frontiers both get about 25 mpg and have more hp than a B2600i).

For your issue, also check that when the engine is cold that the choke butterfly is essentially horizontal, and that after running like 15 minutes that the choke butterfly is essentially vertical. The wire to the choke heater on the carb should be plugged into the rear of the alternator. A choke butterfly that does not open fully can cause a rich-running condition, and the choke position is readily adjustable (adjust to fully open when the engine is warm). I'd also temporarily disconnect the accelerator cable and see if the idle stays high or can be adjusted lower.