1968 GMC 250 Inline 6 4.1L Chugging

[RichardJ]

*
*
*
*
*
*
Confirmed vacuum advance arm is working -- vac adv should be connected to Ported Vacuum port with no advance @ idle with 0 in.hg.
*
Checked vacuum at carb -- Vacuum = ? in.hg. @ rpm, checked WHERE ? Port on manifold or does you carb have manifold vacuum port?
*
Confirmed points/dwell set properly -- With vacuum hose plugged, does dwell stay @31 when engine is revved, With engine @idle, use hand vacuum pump to operate vacuum advance through its full range. Watch timing on balancer with timing light. Again check that dwell stays @ the 31
*
Confirmed RPMs -- What is the Idle rpm with choke off and engine warm
New exhaust -- Did you check the Intake/Exhaust gasket against the head? Look for black soot on the block below the manifolds.

NEW Exhaust? Did you get the LMC exhaust?

[68gmcdude]

Originally Posted by RichardJ

*
*
*
*
*
*
Confirmed vacuum advance arm is working -- vac adv should be connected to Ported Vacuum port with no advance @ idle with 0 in.hg.
*
Checked vacuum at carb -- Vacuum = ? in.hg. @ rpm, checked WHERE ? Port on manifold or does you carb have manifold vacuum port?
*
Confirmed points/dwell set properly -- With vacuum hose plugged, does dwell stay @31 when engine is revved, With engine @idle, use hand vacuum pump to operate vacuum advance through its full range. Watch timing on balancer with timing light. Again check that dwell stays @ the 31
*
Confirmed RPMs -- What is the Idle rpm with choke off and engine warm
New exhaust -- Did you check the Intake/Exhaust gasket against the head? Look for black soot on the block below the manifolds.

NEW Exhaust? Did you get the LMC exhaust?

I'm a do it yourself mechanic so please forgive me if my answers don't make sense or I'm not understanding something..

Vacuum advance is connected to port on carb in the picture I have attached. When disconnecting and checking with vacuum guage and engine at idle the guage read 0. When revving the engine the guage would read up to 20. I did not have a meter hooked up for RPMs when revving the engine.
Idle for this motor with choke off and warmed up is 700rpm. I believe normally it would be 400rpm but according to the shop manual it should be 700rpm because mine has the A.I.R. smog pump.
I have not checked your third suggestion. Will do that.
I ended up getting the LMC exhaust. Ended up working out good.
Thanks for everyone's help... Hope to get this figured out soon.