Carb recommendation - 66 SBC 283 engine

[GTO Geoff]

Rgalajda,
Here is another lesson. It is actually a good idea on older cars that had points ign & resistance wire [ or bal res ] to use a relay to power HEI. HEI is inductive ign. More voltage means more spark energy. Connecting one side of the relay contacts to the alt stud, battery [+] terminal or [+] terminal on the starter will ensure that the HEI gets max voltage; use a 10 amp inline fuse for protection.
My car, a GM car, originally had points ign. With the engine running, there was a voltage drop of 1v at the fuse box. Quite normal. So if I had fed my HEI from the FB, it would have been down 1v compared to the above procedure.


Mark.
Set the idle timing [ init +MVA ] that gives you the highest idle rpm. Forget about idle vacuum. Vac will be highest with highest rpm, they will coincide. The high[er] rpm is the engine making more HP from the timing, whatever that might be. Same deal with idle mixture setting. If you turn the screws & rpm increases, engine is making more HP & likes that setting.
6 Volts will NOT damage the coil.

[rgalajda]

GTO Geoff
I understand your reasoning. Would this be a better solution ?

When running with mostly stock wire harness and HEI, it’s a good idea to install relays for the headlights. With original wire harness, the headlights draw power from the dash wire harness, resulting in lower voltage at the dash area when the lights are switched ON. RELAY kits make the headlight up grade simple, and it does stop the headlights from robbing power from the HEI. Of course, the headlights will be much brighter too.

[GTO Geoff]

Rg,
You are correct. High power items like h/lights, air con compressor, etc it is a good idea to use a relay.

[bigblockmark]

Checked out a few more things on the Chevelle. Used my bore scope to check piston TDC in comparison with the crank damper zero mark at zero on the timing tab on the timing cover. It is dead on as far as I can see. New spark plugs with 15 minutes run time were black with build up on them, but not oily. Took the Holley Avenger carb back off, it was black down the barrels and underneath was covered in black. Checked the power valve, it is not blown. I was wrong on the carb size all along. It is an 80570 so it is a 570 not a 670 like I thought. Primary jets are stock at 54, secondary are 65 stock. New Brawler 570 is back on the car. It had black build up same as the Avenger. It was run when the HEI only had 6 volts going to it and the alternator was not charging. Going to up the initial advance from 4* to 12* right off tomorrow and then add manifold vacuum advance for the distributor. (Had to quit to go watch Street Outlaws on Discovery Channel.)

[bigblockmark]

With the new 570 Brawler carb back on, spark plugs cleaned, initial timing set a 12 degrees and vacuum advance hooked back up. Test drive is much batter. Still a little flat spot leaving a stop light, but that is the sloppy Brawler accelerator pump linkage. Popped a little bit thru the carb at first, but came out of it after a few miles. Took out #3 spark plug and it is not black coated any more. insulator material is light gray.

I had the Avenger apart and noticed the primary metering block has low idle fuel restrictors at .026" and there are no emulsion holes at all. Also has back metering block. Holey book shows it is a 4160 model. Maybe this carb has mismatched parts. The metering block gasket had black streaks vertical in line with the idle air bleeds.

[Right hand drive]

Just spit ballin’ here but have you had the rocker covers off to see if the cam is telling all the valves what to do?

Black under the carb on a stock 283 and even signs of reversion in the idle channel I wonder if there is an exhaust valve barely opening and evacuating the cylinders exhaust, leading to some exhaust backing up the intake on intake opening? Wouldn’t think it would show up on compression and scope test.

[bigblockmark]

I have not had the valve covers off. It has stock hydraulic valve train. It does have aftermarket valve covers, so it is possible someone in the past did adjust them down to make up for valve train noise.Vacuum gauge is steady at 18" at idle. Scope shows even firing voltage. The owner said he has never done that in the last seven years he has owned it, but it is one last thing that would be easy to verify. I did find the the car has a new voltage regulator and I had changed the alternator due to not charging. Still the voltage running was only 13 volts. Traced thru the wiring and the white wire between the regulator and alternator was corroded. cleaned that and now have 14.2 volts running. seems to run better now. Friday the owner will be back in town and going to take it for the weekend. Depending on his satisfaction I may put some more time into diagnosis.

[Right hand drive]

[bigblockmark]

Update again. Phone rang at 8:01 this morning. Qwner agreed it ran better but not the best at first. Got worse the rest of Saturday. Sunday he could not get it to back out of the garage, just kept backfiring out the pipes and carb and died. I went there and did get it back to the shop, but it was backfiring bad and would not go above 20 MPH again or pull itself up a hill. I did a cylinder short test on it at 1500 RPM. Every time it dropped a cylinder it backfired. Balance was all over the place. Pulled the plugs. They were black coated again and insulator was coated black. I did a compression test while plugs were out all 8 were at least 90# on first hit and at least 140# 5th hit. compression is good as can be expected I think. Recleaned the plugs and took it for a teat drive. At mild acceleration it runs with out back fire. I had it up to 70 mph. From a standing stop, If I floor it it does "sneeze" out of the carb and rolling along at cruise if I try to accelerate rapidly it sneezes. It is no ball of fire at any speed when accelerating. Pulled a plug after the 5 mile test and it is dark gray on the insulator, and the flat surface above the threads is already getting black. I believe it will get worse and start back firing again because it is fowling the plugs.

So what is the cause? 2 different carbs do the same basic thing, one brand new 570 Brawler. It has an aftermarket intake manifold installed when the throttle body 4 barrel injection system was installed because it was a 2 barrel carb intake before. That was done because the 2 barrel carb was "smelly" according to his wife. And the injection was removed by me because it did not ever run right after that. Can the Edelbrock Air Gap RPM Plus be the cause? Can the HEI aftermarket distributor be an issue now that it has 14 volts at 1500 RPM verified instead of the 6 volts it had when it came in? The charging system is working properly now when it was not charging when it came in. Can the new plugs be fowled so bad after less that 20 miles and being cleaned 2 times? Can there be an issue with the camshaft even though there is no noticeable noise and cranking compression is even on all cylinders. Can the new Brawler carb have a blown power valve causing it to fowl the plugs? It has an anti back fire check valve circuit, supposedly. The Choke does not work very good also. The adjusting screw for RPM and the 3 step plastic cam barely line up and it slips off to the side. Kinda how the accelerator pump lever slides of the cam lever and does not give instant pump shot. Junk parts i guess.

[GTO Geoff]

[1] 14v to the HEI is ok.

[2] RPM intake might not be the best, but not the cause of the problem.

[3] Could be wiped cam lobe[s].

[4] I would put a good carb on it like an AFB, anything but a Holley or clone.