I have 79 SR5 20r and it randomly started to over heat and idle a bit rough. I tried playing with the carb screws and it didn’t seem to help with the idle. As for the file it ides most rough when it’s cold but continues to idle rough.
What would cause this?
I just replaced the thermostat, and it’s still over heating.
I also just checked timing and it appears to be 11° advanced? This is a stock engine does anyone know the stock advance for a 20r?
According to the manual it’s located on a sticker I don’t have. So hopefully someone can help.

 

8 degrees BTDC is factory timing setting. If you’re running a Weber 32/36 I find 11/12 BTDC is a good setting.

Did you have an over heating problem before you changed the thermostat ?

If not, you may have a bad thermostat.

 

Yeah it randomly started over heating so I thought it was the thermostat. The rough idle and the overheating may not be in common but both happened out of the blue after it had been running fine.
Maybe I need to change the timing to 8° and see if there helps?

 

I changed the timing to 8°. Seemed to help with the idle issue a little bit. Still can’t figure out why it’s over heating.

 

Any contamination of the cooling system at all? Radiator cap isn't funky by any chance? Did you test the old thermostat, if you still have it, to see if it opens? Just thinking what might be a cause here....

 

No contamination that I know of. Radiator cap is funky, but it’s on secure and tight. I tossed the old thermostat.

 

Have you pressure-tested the cooling system? How is the radiator cap funky, too little or too much PSI on it? My cap is a 12-14 lbs cap; not sure about what the 20Rs cooling system is rated at however, could be similar.

 

It doesn’t happen often, but you might have an air bubble in the cooling system.

Try removing the new thermostat and then run the engine without thermostat for several minutes. This will purge any air trapped in the system. Reinstall thermostat and see if that cures your overheating problem.