My 67 3/4 ton 4X4 has a knock/ping under load. It is basicly a stock
390 with the exception of 4v intake 600cfm edlebrock carb and hooker
headers. Timing is set at 10 initial 36 total in by 3000 rpm. I'm
using 89 octane fuel. It runs great but when accelerating up a grade
it starts to knock a little. Any ideas?

 

I'd look at engine ping first. Back the timming 2 deg at a time and see if it goes away. If it goes away then it's just engine pinging, not a real problem if you stop it in time. I've heard that cleaning the carbon of the top of the pistons helps to reduce this.

I rod knock or piston slap would be the next guess, but back off the timming first and see what happens.

Pinging usually happens more on a hot day under load.

 

part throttle ?

bad/wrong vacuum advance mechanics ?

pull the hose

 

Finally had time to play with the truck a little backed the timing
up a couple degrees still pinged a little when i got on it going
up a hill. I backed it off a couple more and no more ping
Seems to have lost a little zip it had but i feel much better with
out the noise and possible damage. Thanks for the help
this forum is the best site for info on these trucks