set my timing so engine wouldn't diesel when hot..,when hot and trying to start it, it is kicking back so bad I almost didn't get it cranked...scared it's going to bend a valve rod or damage something...I have stock 454 with dome pistons and HEI. diributor and Edlbrock 650 carb... engine I guess was built like a 427..anyway...what in the world do I do to solve this problem...motor has 7 blade fan for air conditioning plus electric fan...my temp guage says it never gets over 190 degrees...maybe getting hotter than guage says..thats one thing I can check...suggestions?

 

How are the seals around the radiator that force the incoming air to go through the radiator? Do you have any kind of recovery system for the coolant that gets past the radiator cap as the coolant expands? This system should allow the radiator to draw the coolant back into the radiator as the engine cools. If you have an operational coolant overflow it keeps the radiator full when the car is started the next time. This makes a big difference to how hot the engine runs. Without an overflow recovery system that works the radiator will run partially full and that is not a good thing.

What is the timing set at currently? How much Total Advance does your timing curve allow for? A dial type timing light makes this easier to check if you have one. Do you have any idea which camshaft your engine is using?

If your engine is dieseling after shutdown it can be caused by a couple different things. Normally I would start with pouring cool water down the intake of the carburetor while manually revving the engine. Cooler water will cause any carbon on the pistons or in the cylinder head to break off and get blown out. This was a simple way to stop engine from running on after shutdown IF carbon or hot spots are causing the run on.

Here on the Corvette Forum we have seen more engine running on (dieseling) when their idle screw might be too far in and this exposes a "transfer slot" built into the carburetor body. If the idle screw IS too far in then the solution is to have somebody re-adjust the carburetor to get the transfer slot back down where it belongs. It seems that when the transfer slot is exposed the vacuum can draw extra gas after the engine is shutdown and it starts or promotes "running on" or" dieseling".

What kind of compression are you using in your 427/454? What kind of temperatures does it run while on the road or just sitting in your driveway? It is likely going over the indicated 190* so I would suggest using a infrared thermometer and verify how far off the sensor is reading. It might help to test the temperature gauge or try another sensor. Are you using the cylinder head temperature sensor hole between spark plugs of the drivers side? I am now using the sensor mounted on the intake manifold for my engine's temperature gauge.

Another item that makes engines run hotter is retarded timing. Check your distributor for a good hose on the vacuum advance. If the vacuum advance stops working the temps will start to climb on my 427. I have a MSD Billet Distributor which allows me to use both the centrifugal and vacuum advance mechanisms and the extra ajustability has been useful.

I also have a 1968 C3 with it's 427 and 4 speed but I built my 427 like an L88 engine with the compression and everything forged down below the pistons. My engine runs HOT, I have seen 240* before when I was cruising in the summer months. I modified the timing controls and found a better way to keep it cool. Today I have a Holley EFI system which offers complete control of the timing and ignition settings. My MSD has had the advance mechanisms "locked-out" and the timing control is all done with the fuel injection controller by Holley.

Best regards,
Chris

 

You say you set your timing.

I assume with a dependable timing light and the vacuum adv hose disconnected & plugged.
So what is the magic number your total timing is at currently?

If your temp is 190 ish, I do not believe this is a hot start "kick-back" issue.
But rather some ridiculously high initial setting.

 

the engine like I said is a 1971 stock 454..newly rebuilt...maybe 20 miles on it...I have the old style timing light so I have been guessing on the timing..I need to get one to work with HEI distributor...and get a thermal thermometor....got to start somewhere

 

Bingo ! Guessing at the timing. Been there, done that, when I didn't have the money to buy a stupid timing light.
Now, a hundred yrs later, still don't have the money, but bought one anyway.

Some Timing Lights have difficulty reading the more modern HEI systems. They have to pick up the pulse from the plugwire, figure out what the signal is, then activate the light flash itself. All under a millisecond.
And that is why the strobe mark on the harmonic balancer appears to dance around sometimes.
It's not the timing chain. It's not the distributor. It's not the cap & rotor. It's the light.

I have a "Dial-back" from Summit, but someone will tell you the better units to buy, with a tach included.

 

Also be aware that newly rebuilt engine will produce more friction/HEAT as they continue to break-in. Header coatings are not supposed to be used on engine before they are fully broken in, the extra heat can burn the coatings permanently and change their appearance.

I have an old sears and fastbuck dial back timing light from the 1980's and it works great on my HEI (C4) and my MSD distributor (C3).

Doe you have a harmonic balancer marked with the degree's or is it the simple marking used by the factory? It is not that hard to set the timing without running the engine for initial setup of the timing.

One more question, you have both a 7 blade mechanical fan and an electric fan for cooling the radiator. How far in does the mechanical fan go into the Radiator Shroud? For a mechanical fan to work effectively you need a "working" thermal clutch on it and the fan must reach inside the radiator shroud to be able to pull the most airflow. Where is the electric fan on this engine? Is it pushing the air into the radiator or pulling through the radiator? Have you cleaned out the space between the radiator and your A/C's condenser. Sometimes leaf and other matter builds up in there on some air conditioned Corvettes.

Is the engine still running-on after shutting down the ignition? It could very well be the timing is too advanced causing the engine to have to work hard to spin the engine over. If the engine still runs on (dieseling) then the timing could still be part of the problem. My 427 likes 36*-38* total timing for it to make the most power. My starter worked really hard to start the engine when hot until I was able to "unload" the starter during the cranking mode. You need to verify that both your vacuum and mechanical advance mechanisms are working properly. It takes both of them to get the timing to the the 36* of total timing when running at 3000 rpm.

The reason I asked earlier, where the temperature sender is on your engine. On the side of the cylinder head, the temperature sender can read a more steady, stable number on the temp gauge. On top of the intake it moves around more because it is in direct contact with the coolant. The side mounting hole for the sending unit does not have direct coolant contact, as it is the "cylinder head's" temperature.

The Intake manifold upper temperature sender location can read a "steady" number when the coolant level is low or if an air pocket is trapped in the thermostat housing. When the coolant level was higher and there was no air trapped inside the thermostat housing the sensor had fluid touching it and read a changing number of the coolant passing by it. My 1968 BB can hold a small amount of air inside the body of the thermostat housing as it is one of the highest points in the cooling system.

I apologize if I am not explaining it clearly, basically air trapped in the coolant loop can cause issues for the engine's cooling ability. I do not have to Burp my engine or anything like that. While the front end is on ramps I will loosen the sending unit until I get coolant leaking out the threads and it is done, on my 427 BB. I don't have a stock type of thermostat housing on my engine, it swivels and has an extra hole for another sending unit.

Please let us know what you find as you work on your Corvette. The help is "free" but we here, like to learn what made your issue an issue so we can help others avoid the same problem. That can only come from you after you fix your Corvette!

 

What Chris /|\ said.
I had some initial 'running-on' issues with my 489 stroker when freshly built and very new...........and the reason? an overly rich idle mixture required due to poor vacuum at idle (due to cam). My reckoning was that carbon deposits were retaining combustion heat on sharp new edges of machined piston valve reliefs and combustion chambers. If a manual transmission you can stop the engine in gear. I'm running an initial advance of 22 degree at idle so certainly wasn't a retarded ignition issue. Poor quality gas doesn't help........getting a few miles on the engine helped - as did weakening the idle mixture. And yes, I did later have a 'kick-back' issue once when starting which broke a tooth off the OEM starter pinion......

 

Did you advance or retard it? Did you mark it in any way before moving it so you can go back to where it was?

 

Sorry guys ..I have been remodeling bath ..everything on the engine is new......have not had the chance to do anything with timing...will update sometime later...