Posted by Dave in CA [108.162.215.103] on Monday, October 23, 2017 at 11:42:24 :
In Reply to: Still Overheating (Some) posted by Jim in Litchfield Park [162.158.142.7] on Sunday, October 22, 2017 at 22:25:23 :
Once you eliminate a head gasket leak or a fan moving air in the wrong direction, you need to have sufficient ignition advance and the correct air/fuel mixture. If you don’t have a degreed balancer or an adjustable timing light, a $10 timing tape on the harmonic balancer will allow you to set advance properly. A wide band oxygen sensor, plumbed into the exhaust system, with an air/fuel ratio readout (I use one made by NGK) will allow you to get the right jetting and metering rod combination. A vacuum gauge, in conjunction with the air/fuel readout, will allow you to pick the right metering rod springs. On a similar motor, running the Chrysler electronic ignition and Carter 4-barrel carb, I run 35 degrees advance under load, 10 initial + 25 on the distributor, all of which is available by 2000 rpm. At cruise, I have 50 degrees total, with 15 degrees of vacuum advance added to the 35 degrees of mechanical advance. The stumble and leaning out under load was caused by weak (only 4 in Hg) metering rod springs. This means that until the throttle is opened wide enough to drop the vacuum below 4 in Hg, the rods will not raise to enrichen the mixture. On the Edelbrock carbs, you can tell which springs your carb has by the color: Blue is 3 in Hg, yellow is 4 in Hg, orange is 5 in Hg, pink is 7 in Hg, and silver is 8 in Hg. In general, you want to pick a spring that is rated a little below your idle vacuum.
The old timers who did “power tuning” to set the advance were pretty smart, and approximate what you’re trying to do when you want to avoid overheating. In power tuning, the ignition was advanced until the motor pinged under load, then retarded a degree or two and locked down. They ended up with the most complete burn they could achieve, with the fuel they were using. The fuel was not continuing to burn any longer than necessary and just generating heat, rather than power. A higher-octane fuel will allow you to run more advance, but you need to run the lowest octane fuel that won’t ping after setting the mechanical advance close to optimal for your engine, which is in the range of 34 to 37 degrees, if I recall correctly.
Lastly, watch out for poor quality, Chinese made, thermostats. They are even sold by American companies that used to sell only quality parts. I bought a Mr. Gasket thermostat for $15, which was made in China, and it failed within the first few hundred miles. I ended up buying a Milodon thermostat for $25, which is made in the USA, and it has been reliable.
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