Quote:
Originally Posted by Gromit
I did notice the 850 RPM idle speed you mentioned sounded about 200 RPMs high but since some people like what I would consider a high idle so I didn't want to judge.. I prefer a putta-put-put - maximum 650 RPM or as low as I can get it to run smoothly in that neighborhood.
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I did test your theory, I used to have a Harley so I like the Potato Potato low idle rumble too! lol So I tested at 700 RPM idle which yielded a 500 RPM while stopped in Drive or in Reverse. Truck did not like that real low 500 RPM and would shake and hesitate and really struggle idling smoothly. Also there was no change in the overheating, again it was fine in Park/Neutral and temps started climbing in Drive/Reverse with my foot on the brake. So I had to pump the RPM at idle back to 800 where it is happiest, but it was worth a try.
Quote:
Originally Posted by Gromit
You definitely don't want your centrifugal advance coming in at whatever idle you wanna use.
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I wonder if you are on to something. The idle timing with manifold vacuum is 35* (13.5 initial + 14 vacuum? + 7.5 centrifugal?) that would mean I may need to adjust my ignition curve as the mechanical is coming in too early. I don't recall what color springs I am running on this Accel HEI distributor, may be time to check. My vacuum canister is adjustable so I may be able to take some advance out that way too.
Here is a brilliant article by Jeff Smith:
Understanding Vacuum Advance and Why You Need It
Quote:
Originally Posted by Gromit
Hey I may have been wrong about your initial timing being the cause of your overheating...
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Hey, don't count yourself out just yet brother, I know for a fact timing was the initial culprit. Remember when I discovered I had a bad vacuum advance canister, well, replacing that can fixed my overheating problem at idle, ie in Park/Neutral, since the truck likes Manifold Vacuum, ie lots of advance at idle