I have a 1985 K5, 305 engine. I just rebuilt the Carb, Carter AFB 9000 series 4bbl. The Blazer was running real, bad, with black discharge and no power. After rebuilding the carb (which looks as though it has never been done) the K5 runs awesome with plenty of power unless you stomp the accelerator. You can quickly accelerate but just not stomp it. This occurs under load or in park. I checked fuel pressure which was fine and even checked the engine vaccum which was normal.

Tuned up a year ago and have only put maybe 1,000 miles since then, does not appear to be missing.

I changed the metering rods and springs which made it run better but did not solve the problem.

Cat. float settings or something else (double checked float hieght settings but who knows)?

 

If it happens immediately on WOT, and just falls on face, probably coil

 

Good call on the coil, needed changing but even though it drives better still stalls at W.O.T.

Next going to check timingi tried to find the timing mark, I believe on this 85 305 it is at twelve o'clock, possibly have to look behind the water pump?

Any tips on finding it and setting timing?

 

Well, I had a brain fart on that.
1. Accel pump
2. Secondary venturi

You specify 9000 series, but you need to address the CFM rating.

Check tag {hopefully has one} and compare to chart

Carter AFB Carburetor

Also here's a detailed doc on the afb series that may help
http://www.mymopar.com/downloads/carterafbtuning.pdf

I vaguely recall having a little of same problem on my 285/260 hp with AFB. I THINK I somehow adjusted secondary to never open all the way. Even a 640 cfm is a lot of carb for a mid CI SB

 

Yes I agree I was concerned about that when I researched the carb before I rebuilt it, I am sure back in the late 80's some red neck like me slapped it on there thinking bigger is better.

I am going to attempt the timing first cause it is backfiring from the carb.

 

Well, adjusted timing which was way off. Runs awesome but still dies when I stomp the gas! In park or underload but only from a dead stop. Other than that is is running great was even able to chirp the big mudders when taking off.

I guess I will get some smaller jets and replace them on a rainy day.

Is there something I am leaving out? Would it be worth the time to check the CAT? It is the original exhaust, looks in great shape but rusted pretty tight so I am afraid getting that CAT off could damage the exhaust.

 

WAIT A MINUTE. It's not necessarily jets.. It's that you stomp it, You're dumping into a LEAN condition. Disconnect the secondary linkage and see how it handles it.

That's why proper accelerator pump and secondary size matters. You dont draw fuel through the secondary venturis if you dont have sufficient airflow. That's why some carbs incorporated power valves for the secondary and others added on 'vacuum' enabled linkage.Blocked cat = low power at rpm. Not out of hole, necessarily.

PBlaster for several days plus heat does wonders.