Dropping Engine RPM's and Stalling
I have a 1969 Z/28 with the factory 302. I take it out only about once every 2-3 months. I drive it on a combination street and highway route that totals about 36 miles. Beginning about a year ago every so often when I had travelled most of the route and was heading home whenever I stopped at a red light the idle would drop down to about 500-600 rpm; normally it idles around 1,000. This would make me wish I had a third foot to keep the idle up while stopped. This problem seems to have gotten worse over the past year. Sometimes it will die completely at a stop and then is really hard to restart. It does seem to happen more often and get worse the hotter the weather is. The temp gauge never reads above the second small line past the first quarter mark on the gauge so I don't think the engine is running hot. When I turn the engine off it does go up to the halfway mark or a little above, but I have been told this is normal with the fan not running after turning the engine off after it was running at normal operating temperature for awhile.
Sometimes this above described problem never happens. I never know ahead of time when it will though. The other day in my driveway the engine kept killing and wouldn't even idle after just a short drive. It seemed to do this more when I had it in reverse as opposed to first gear. I've had the carb tuned and adjusted, front float adjusted and a new power valve and needle and seat installed.
I've been told that the valves might be too tight and that this would cause the engine to not idle right and that they should be adjusted. The car seems to run fine under acceleration and holding a steady speed; it just won't keep the idle up where it should be. I am not experienced enough myself to diagnose correctly this problem and unfortunately haven't been able to find a mechanic that can either.
What do you guys think? Any ideas or other things I should try or look into? Thank you.