Rough idle and takeoff 250 inline

[68gmcdude]

Originally Posted by '68OrangeSunshine

68gmcdude -- What's your Odometer reading?

Just over 55k original miles.

[68gmcdude]

Originally Posted by Rust_never_sleeps

Insulting question: you're setting the static timing with vacuum advance disconnected and plugged?
Also, vac advance is functional? (moves freely when vacuum is applied to the hose)

Yes to both questions...

[68gmcdude]

I checked for leaks around the intake manifold by spraying starting fluid then checking the bolts. No leaks found and all bolts were tight.
I advanced the timing to 6⁰ and took for a ride. Idle seems better but still off a little. Takeoffs were good with no backfires. The truck is a 3 speed manual. Seems a little off when I'm cruising at 30mph and I'm in 3rd gear. No problem accelerating from that speed or any other cruising speed though. Runs beautiful on the freeway at 65mph.
So I was always under the impression that advancing the timing was a bad thing. Evidently not as it seems a lot of people do it. Should I advance it even more?

[geezer#99]

Of course!
Jump right in the deep end of the pool.
Go right to 12.

What’s your idle vacuum?

['68OrangeSunshine]

What Geezer said.

About Advanced Timing. When these trucks were new, American gasoline was the best in the world. The Tetra Ethyl Lead created a cushion for pistons and valves. Zinc in the oil helped the lifters slide on the cam lobes easy. And Timing was good at TDC.
Since we're dealing with a totally different blend of automotive fuels today, with additives and ethanol, we have to compensate by advancing the timing.

[67 twins]

The only danger in advsncing the timing is going to far & causing detonation. As Geezer#99 said go to 12 & test drive it while listening for detonation on acceleration. If you experience no detonation then your good. Then enjoy the increase in power and trouble free driving.

[mr48chev]

Ran great until you got home from a 400 mile road trip?

Think back, where did you buy gas on that road trip? I'm a picky bugger and I don't care if I have to pay more but only buy gas at newer high volume stations or at Costco stations and never at old former gas station mini marts or cute/quaint out of the way stations.

My brother in law drove fuel truck for several years and Costco is the absolute pickiest about fuel delivery. They don't let drivers stick the tank because the stick on the truck might have contamination on it. Most high volume truck stop or similar stations move enough gas that they never get water or contaminates.

Before you go nuts run the gas in the tank out and down as low as you feel safe with and go fill up at the local station that you normally fill up and see how it acts.

I wouldn't put it past dirt or crud in the carb but at least think back to where you bought gas on the trip and when it started acting up.