1970 Chevy C20 sluggish and bogs out?

[1970 C20 Surf Wagon]

I have a 1970 Chevy C20 truck w/ a fresh stock 350, headers, electronic ignition, new plugs, wires and alternator. It ran and sounded great for about 500 miles. All of a sudden it goes from roaring to puttering, I cant give it too much gas cuz it wants to stall. It feels as if its starving for gas but the clear filter is full, the gas pump is new. One of the funnest parts about driving the truck is its fast starts and great sound with dual exhaust all the way to the rear. I hope some one has ideas for me to try, it has a older Q-Jet that was rebuilt about 5yrs ago.

[TexasT]

have you checked the filter in the q-jet where the fuel line threads on? Is the fuel line new? Are there sections of rubber hose that could be collapsing and/or deteriorating from the inside?

[1970 C20 Surf Wagon]

Thanks Rich, Well so far I have changed the filter in the q-jet, the fuel line, the fuel pump and all the rubber hoses starting from the tank, that sits behind the seat in the cab. Its kinda embarrassing I was climbing a long hill today and I had to go real slow cuz if I give it allot of gas it bogs out and starts to cough. Big nice Chevy truck w/ a new motor and I gotta crawl up hills.

[TexasT]

So, it idles good and runs good as long as there is no load? is the vacuum advance working? There are some nylon bushings in there that get deteriorated over time. do you have a timing light that can show you that the distributor is adding advance as it should with rpm ?

[AzDon]

There are a whole lot of things that can cause this! A carburetor has five circuits that handle different rpm stages and load circumstances. It's not necessarily metering fuel just because fuel being provided to it. Carburetors provide fuel to the engine as the result of the engine vacuuming it from the designated openings in the carb. Any dirt in the passageways will disrupt this flow.
Another requirement for a carb to work is that the engine has proper vacuum. If the cam chain and gears have jumped timing, the engine may still barely run at an idle but sputter out with the slightest change of throttle position.
I would first put a timing light on the engine to assure that the timing is correct.
I would then swap out that QJ for a carb that I fully understand... a holley double pumper. Maybe before I did the carb swap, I'd make sure the distributor shaft is not loose in worn bearings and that the centrifugal advance mechanism isnt frozen. Also, I'd suck on the vacuum advance hose to make sure that diaphram is working.
Couple of other things: Vacuum leaks, especially manifold vacuum leaks can be a problem. things to check: hoses to the pcv valve, power brake booster and trans modulator. The trans modulator can also have a bad diaphram (do the suck test, and if you get atf out of the hose, replace the modulator)
Check for vacuum leaks around the carb by spraying wd40 or carb cleaner around the carb and along the intake manifold mating surfaces with the engine running and listen for an increase in RPM. DO NOT spray on exhaust maifolds unless you like dealing with FIRE

[capev86]

dielectric grease needed? modern GM products love that stuff and probably a good idea on your truck also.

my dad had episodes of sluggish performance with his 87 burb 350 tbi. after spending big bucks on a new distributor, he found out about using dielectric grease in all the plug wire boots, etc. a fresh coat of grease was just the ticket on several occasions over the years.

[magicoolbus]

Could be a clogged fuel pick up in the tank.

[simp50]

the float in the carborator could be bad. it'll make ur motor sound like its flooding and you will burn gas.