Carb recommendation - 66 SBC 283 engine

[Nick_nl]

I have also used a 570 cfm brawler carb on my 283. It never ran right. On the old board a very long thread is about this problem. You need to take it apart and check all orifices and plug the unnecessary holes according to gntkillers recipe.

[rgalajda]

If it ran good enough for the owner to drive it with the 670 cfm carb then it should with the new 570 cfm carb. I have never installed a properly sized new carb that did not perform well on a mild engine. You had the cap and wires off for testing before installing the new carb. Now it backfires. Maybe do some backtracking.
Double check plug wiring and cap installation. Ohmeter readings for plug wires is part of the puzzle. Confirm no 1 location on distributor cap and firing order 18436572. Remember someone could have installed the distributor one tooth off and moved the wires on the cap to coincide.
Personally I prefer to install new wires unless they look new.

[Nick_nl]

Did you already verify that the timing mark is correct? These old crank dampers slip over time. Also, the 66 had points, so the current distributor has been charged, but is the resistor (wire) also bypassed?

[bigblockmark]

When the rotor is pointing at the #1 position on the cap, the timing mark on the damper is lined up with zero on the timing pointer on the timing cover, so I think it is correct, but it sounds like it has too much timing. If I retard the distributor, the vacuum falls off fast and rpm drops enough I have to turn the idle screw in pretty far. Could the timing chain have jumped a tooth? Could it have done that and the timing marks still be lined up? I put the old 670 Avenger carb back on and it does run better at idle than the new Brawler 570, but it back fires out the carb if try to give it any throttle moderately. Cant get it too accelerate on the road with out it backfiring and just about dieing. also back fires out the exhaust when trying to accelerate.

Did not check the voltage to the HEI. Good suggestion.

[Right hand drive]

[bigblockmark]

I checked out the HEI power wire. The HEI plug wire to the distributor is butt splice to 2 original wire loom wires, one being the old fiber braided one. It wouud have 12 volts to start and then run on 6 volts originally correct? Turning the key on the plug shows 12 volts, but may go to 6 volts after starts right? I hot wired off the alternator output post. Did not seem to improve anything though. That is when i read out with a meter and alternator is not working. 12.16 volts reved up. So running off the battery only. That might explain why the owner said the further he drove it the worse it ran? It would not start the next morning when he was going to bring it back and he went and bought a new battery. New alternator and proper wired 12 volts to distributor and we will see if that changes anything. Thanks for the suggestions. Will check out piston TDC and crank damper zero degree in the morning. Hope it is not a tooth jumped on the timing chain.

[6.50camaro]

If I remember correct chevys of that era got 12v off the starter thru the key switch for starting then its power source in the run key position for ignition went thru a resistive wire lowering the voltage to ? (don't remember) so the points didn't burn out. For an HEI you need power with full 12v source all the time from start to run key positions . I took a 12v source out of the fuse box run it thru a relay switched by the original resistor wire going to dist. It was always pulled the relay in and has not failed me in 7 years . I hope this helps. Dan

[GTO Geoff]

This is where a little knowledge .....is dangerous. The typical automotive relay will operate by connecting it to the original resistance wire. It 'works' because the relay has a 70 ohm coil & the res wire [ or bal res ] is about 0.5 ohms. So the relay gets almost all of the 12v & can draw more than enough current through the res wire to operate. Remove the relay & hook up a HEI module in it's place. The typical HEI coil has a primary res of about 0.6 ohms, say 0.5 ohms for easy maths. With the res wire still in the cct, the res wire gets 6 volts out of the available 12v & the coil gets the left over 6v [ not 12v as it was designed to do ].
The lessons here are:
- that because a 12v relay operates, it does not mean that there is sufficient current & voltage to operate another 12v device that requires more current.
- taking ign voltage readings without the engine running can give misleading readings.

[rgalajda]

This is getting embarrassing. HEI hooked to alternator? Relays to run an HEI ignition . Then a lesson on relays.

Not all relays work as explained

A 1966 chevy has a voltage regulator outside of the alternator (unless its been converted]
The HEI ignition needs 12 volts from the ignition side of the fuse panel. No relay.

[bigblockmark]

I have replaced the alternator with a NAPA rebuilt one. Ran a new 12 volt wire to the HEI direct from the fuse block under the dash. (It has 2 12 volt ignition Lugs.) Battery is charging from alternator now. Shows 12.8 volts after shut off for 15 minutes .

Engine idles smoother. Will rev up better when opening the carb up. The miss seems to be going away. Tried to test drive it and it is still dong the same popping back out of the carb when trying to accelerate but not out of the exhaust, so not fixed.

I reset the distributor to highest vacuum and reset the idle A/F screws. Best at only 1/2 turn out.This is still with the Avenger 670 carb. It only has 4* initial time right now. Going to move that back up to maybe 14* and readjust carb RPM down as it gets too high. Maybe the new plugs got fouled due to the 6 volts? I will pull and clean. Maybe the coil got damaged by the 6 volts? Still have not checked TDC and timing mark at zero agree. Also switch back to the new Brawler 570. I only get a couple hours at a time to work with it.