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I bought a ‘71 coupe in July that was consigned to a dealer after the passing of the owner, so I don’t know much of the car’s history. There was a lot of stuff wrong with it, but I’ve made good progress EXCEPT with ignition timing. I set the dwell and timing and it runs good for 20 or 30 minutes then the timing retards and it runs crappy. Rinse and repeat. I have changed cap, rotor, points and condenser (2 sets), wires, and plugs. Can anyone suggest what I should look at next? It’s a base small block.
Hello kb,
Welcome!
Your 71 base engine originally had a 'Combined Emission Control' system.
If it's still on your engine but not operating properly it could be causing you some timing issues when the engine reaches operating temperatures.
Is its there?
Regards....
This system affects idle rpm when the engine is cold and when it's warmed up.
Nope, not there. The engine is not from a ‘71 but the ID is ground off (stolen?) so not sure. Intake manifold casting number is from a ‘73. Carburetor is aftermarket Holley slant bore QJ replacement.
I bought a ‘71 coupe in July that was consigned to a dealer after the passing of the owner, so I don’t know much of the car’s history. There was a lot of stuff wrong with it, but I’ve made good progress EXCEPT with ignition timing. I set the dwell and timing and it runs good for 20 or 30 minutes then the timing retards and it runs crappy. Rinse and repeat. I have changed cap, rotor, points and condenser (2 sets), wires, and plugs. Can anyone suggest what I should look at next? It’s a base small block.
Curious about this self-adjusting timing... You set it to 12° and it resets itself to what? Are you sure the distributor clamp is on the distributor shoulder and snugged down? Is your bolt too long and not clamping securely?
Clamp is tight. I cannot budge the distributor by hand. The last time I pulled the cap and rotor and the points had closed almost all of the way at the high point of the distributor cam. I read that some new replacement point sets have a phenolic rub block that would soften with heat and would wear super fast, causing just what was happening with mine. I changed to NAPA points as suggested elsewhere in this forum but problem remains. I am stumped at the moment.
If the rubbing block is no longer wearing either the points plate is moving allowing the points to close or you have side play in the distributor shaft?
12 BTDC at idle, 30 BTDC at 3,000 RPM with vacuum advance disconnected. The car was completely warmed up and the choke was off.
You need another 6 degrees of advance.
Dwell can't move but the distributor can....set it again, lock it down and make a mark at the base of the distributor and intake with a sharpie....inspect later for movement.
Also....it isn't just 3000 rpm....it may go higher....rev higher until the mark quits climbing....
In order to best approach this motor as you move ahead, I suggest you make every attempt (to the best of your ability) identify it; from those clues that probably do exist.
Find the block casting Number (driver side rear ledge aka shelf between rear of driver valve cover and bellhousing (the ledge faces Up) Number characters are Raised.
Find the block casting Date (pass side rear ledge aka shelf between rear of pass valve cover and bellhousing (the ledge faces Up) Date characters are raised and are alphanumeric.
Find EACH Cylinder head's casting Number And casting Date (underneath valve cover) they're both raised and date is alphanumeric code. Located around the valve springs. Verify Both heads for match, No-match.
Casting numbers and dates can help to narrow identity of motor that you have. ID which type and displacement, its year of production, perhaps help ID which vehicle it was initially installed in.
** rubbing block made of phenolic resin is not, in and of itself, a bad thing. Perhaps the particular recipe of resin has been unworthy. But plenty of Very old contact sets had good quality rubbing blocks made of phenolic resin. Other newer sets have had rubbing blocks made of some neutral color plastic and some of those didn't wear well either.
Points Cam Lobes have always Required Lube with a specific points lobe grease. Can be Hard to find nowadays. It's available from Standard Motor Products aka Standard Ignition as part number SL-2 for a small tube that'll last a lifetime. Just a thin coating of cam does it, plus if there's an adjoining wiper-wick, just a dab onto it as well. RockAuto and Summit sell it.
Last edited by Rebelyell; Dec 29, 2025 at 10:19 PM.
Reason: contact points
sounds like your distributer has a issue, I would get a new small head tack drive HEI distributer and be done with it, I put those on all my old vettes
they work great
Also....it isn't just 3000 rpm....it may go higher....rev higher until the mark quits climbing.
You can also remove the springs, disconnect the vacuum and set the 36 degrees at idle, then play with springs until it's all in at 3,000 rpm. I hate having my face two feet from the fan blades with the motor running at 4,000 rpm.
Also suggest you pull the distributor and go through it per Lars' paper on the subject. Take out the end play. inspect the gear, clean and lube the shaft and set the centrifugal and vacuum advance to the right numbers.
Hijacking a tread a bit but if you have all of the Combined Emission Control system removed from the car (from the carburetor and the sensor in the passenger side cylinder head) do you still have to connect the connectors on the relays on the firewall? Would that cause any issues?
I'm thinking that your vacuum advance or your mechanical advance is sticking in the advanced position and once warmed up it's moving freely to it's resting position....and thus the retarded timing. Once cooled down and the engine is started again to set timing (for the 100th time) it sticks again and the process repeats.
I'd pull the top of the distributor off and the rotor off, and have a close look at the components to confirm that everything is working as it should. Use a vacuum pump to test the vacuum advance.
Ignition Timing Issues
