On my 66 C20 with a 2 barrel carburetor I had taken it to the mechanic a little over a month ago for valve adjustment since it was making noises on the passenger side

I notice the truck backfiring from the carburetor at high speeds and it felt almost like it was breaking while driving but the breaking was from the engine not the brakes

any how I decided to check the valve adjustment and I loosened the nuts just a little bit and the valves by piston #8 the one closest to the firewall was barely moving

I loosened till I saw it moving freely like the rest of the valves and check to make sure there where not too loose

that seems to fix the problems I was having
my question is for the experts here
can valves tighten too much create this backfiring and breaking issues?

i drove it around the block and it drove way better no problems so far no backfiring or breaking sensation

I must mention that I did took it back to the mechanic to see what the problem was since I didn’t had this problems before
all he said was that I need it to rebuild the engine

and also he had left the bolt for the distributor loose luckily I check and did the timing before doing the valve adjustment the old way

old man is retired working out of his garage maybe is time to find another mechanic but is hard to find mechanics that know how to work on this old trucks

i had also rebuild the carburetor and replaced the spark plugs and wires and the fuel pump water hoses etc because that’s what he said it was part of the problem but it never went away

till now that I loosened the valves less than a quarter turn except for the #8 I don’t know if it was intake or exhaust valve but it was too tight
I think it was exhaust valve

 

could be cam and lifters. as rocker arms dont adjust them selves . I had exhaust lobe /lifter go out in a 283 and backfires were common till I replaced cam and lifters