Yes, this sloppy throttle linkage is a common problem for these engines. Believe it or not, the slop usually comes from the plastic shaft and the way it fits into the two plastic gears…
#52, 53, and 65 The square ends of the plastic shaft get sloppy inside the two gears.
What makes you think the thermostat is stuck open? Is the engine actually running cold? If so, the thermostat water cover can be removed without pulling the powerhead, but it is a pain in the butt…Start by removing the cover latch to gain a little more room behind the water cover. Loosening up the two rear lower motor pan mounts will help also, this might allow the lower pan to drop down just a bit. Don’t remove the mount bolts completely, the mount washers will slide out and get lost in the lower motor cover.
Has this engine been used in salt water? If so, you may want to consider doing a more thorough cooling system overhaul which does involve pulling the powerhead. Changes were made the the upper water tube grommet in 1979 which were troublesome. The grommet is not fully supported by the water tube, which allows salt to collapse the grommet above the top of the water tube……
