1980 20r Tuning Difficulty
 

I posted in Newbie Tech about two weeks ago and didn't find a solution, so I'm hoping someone here will have some more insight. I have a 1980 4x4 pickup, 20r, 4spd L43 with a new weber 32/36 manual choke and Heddman header. Trying to get it going again after getting the top end redone. This my first major engine work.

My issue:
Truck starts just fine, but idles rough and slowly, misfiring or backfiring (not 100% sure how to tell the differences) occasionally. The header gets red hot after running for about 5 minutes. When throttle is applied, the engine bogs down or dies.

What I've done so far:
-Initially thought it was timing, so I struggled trying to adjust the timing with no success. The timing mark shows that it is set at ~12-15 degrees after TDC in the position that it runs (displaying the above conditions). Adjusting the timing causes a no-start or engine failure. Thinking I may have rushed the reassembly, I removed the timing cover and oil pan, set the engine at TDC (ensuring the #1 cylinder rockers were both loose), and reset the timing chain on the cam drive gear and crankshaft timing gear using the timing marks. The double chain timing set is new since the head work.
-Suspected carburetor problems (brand new pseudo-Weber). New adapter set with new gaskets, carefully went through set-up, removed and inspected jets, floats, idle screw, etc and reinstalled. Installed fuel pressure regulator, which indicates that the carb is receiving 2-3 psi. Checked for vacuum leaks around the carb by spraying carb cleaner on it. The truck has the entire emissions system removed, so there are only 3 vacuum lines (booster and the two advance lines). All are new with new hose clamps on the booster line.
-Checked valve lash per my Chilton guide
-The tank has fresh gas in it

I'm totally lost, sad to say. Hope someone out there can guide me in the right direction :think:

If the exhaust header is glowing red in my experience it has been because of timing. Have you checked with a timing light? Is the distributor installed properly? What are your mixture screws set at?

Was the truck running before the work was done? If so were any of the issues present?

Glowing header could be a variety of things. What do you have for an exhaust system? Possible that could be plugged up.

As far as timing goes, if you turn the dist (either direction) while the truck is running it just immediately dies? May have bigger issues if that is the case. 12-15 sounds about right but I always prefer to time my vehicles by ear.

12 to 15* AFTER TDC? that sounds wrong

Before top dead center. Mine is set at 14 that what it likes best, but I only run premium fuel. Factory recommends 5 btdc for 22r. People usually prefer around 8btdc with a stock 22r on 87 octane.

I have almost the exact same set up. A 1980 4X4 with a 20R, Weber 38/38 and thorley header. Timing should be 8 degrees Before TDC. If it is running at 12 degrees After TDC, something is way wrong!. I'm old school, I use a vacuum guage and ears to set my timing. If you are truly after TDC, you have the distributor in a tooth or two off.

Well I had a friend who's super into Landcruisers help me out and we finally got it running decently with the proper timing. We carefully redid the valve lash and adjusted the carburetor as well. The engine idles like a dream and it revs, but it backfires out of the carb at ~3K RPM. To me this indicates a lean fuel condition, however, I have been absolutely thrashing spark plugs with black buildup. Currently there is a new set of NGK iridium plugs in it that have only been run for about 10 minutes, with no change in backfiring behavior. There is also black gunk shooting out of the exhaust, making a delightful mess all over the wall and the hood that I had leaned against it. Next chance I get, I'll be doing another intake vacuum test. Anyone had experience with this kind of backfiring before?

Check spark plug gaps make sure they are within spec, and I wouldn't use an iridium spark plug in a 22r, they'll run just the same or better with copper NGK or Denso. Also check rotor and cap, make sure your vacuum timing advance is working.

The cap, rotor, wires, and ignition module are all new (gm ignition module) and the coil has been tested per the FSM and is within specs. The vacuum advance was tested by disconnecting it and sucking on it while using a timing light. Iridium plugs do not have adjustable gap as far as I know. The last set of plugs I used I checked the gap and ensured they were all within spec. I checked for vacuum leaks by disconnecting my brake booster line and blowing hella cigar smoke into it, no leaks that I could see.