I have a 1985 K5 with 305 and 70,000 original miles. About a year ago I rebuilt the carb which is a Carter AFB 4b with electric choke. The Blazer ran alot better but would die at WOT and while trying to tune it and sometimes it would backfire through the carb at WOT. I tried several things but I just drive it around town and don't ever stomp it so I was going to pull the carb and check the float levels when I had a chance. I thought maybe the choke was off and tried adjusting it and tuning the carb again. I checked the timing and it was off set it at factory specs, 4. Now it began to clatter under load (uphill, while towing) and sometimes dies after letting off the gas. So I adjusted the timing to 10 based on reading alot of people go to 8 or 10 after putting an after market 4b carb on. I drove it around the block and it had a ton of power, did not die at WOT, in fact chirped the tires (large mud tires at that). I went inside and realized I did not hook the Vacuum Advance back up. I hooked it up, drove around the block again and it ran terrible, more clatter and not as much power, although it did not die at WOT.

I have read this problem with the vacuum advance being disconnected alot but no one ever seems to post what the solution was. But most times it has been when people are dealing with the carb.

I feel like I have had problems related to the carb since I bought the truck I was thinking of just buying a new Edelbrock (they ususally come pretty much tuned right). I suck at tuning the carb and I am not sure the choke is even working properly.

 

Sorry vacuum advance not assist!

 

If you can't tune your Carter AFB then an Edelbrock won't do you much good because they are the same thing.

I'll assume that you are plugging the vacuum line when you're setting the timing.

For your issues I would look at the mechanical and vacuum advance on the distributor. Assuming that it is original to the vehicle it might be time to replace it. For under $200 you can get a good HEI from Mallory, MSD or any other good brand name that will work well for you.

 

Are you sure the advance springs are working properly in the distributor? If they're stuck, it can cause all sorts of problems like you're having.

 

Yall are right they are the same carb, I am just getting frustrated, I did order a new distributor, it probably needs one any way and the Vacuum advance looks like it has barnacles on it. I am going to pull the carb as well and measure the floats again, make sure all the gaskets are good and sealed. I was just thinking at least a new or remanufactured carb will come tuned pretty close and only need minor adjustments. I actually think I have it tuned pretty well but something is causing it to die at WOT, which if it is not the distributor then I probably am off on the floats.

 

The only external adjustments on the Carter AFB / Edelbrock are the stroke of the accelerator pump and the A/F screws on the front. Turning them all the way snug then backing off 2.5 turns is the base setting.

Beyond that it is your jets and metering rod springs.

Have you checked for vacuum leaks?

 

Yeah prior to this post I went back and put the screws at 1 1/2 turns and adjusted from that point, I had backed them to far out tryinging to adjust it and I fixed the chock plate that was sticking which did not change anything. The only thing that has made a difference is when I accidentally left the vacuum advance plugged after adjusting the timing it ran almost perfect. I have a new distributor on the way which even if that is not the cause it needs replacing anyway.

Vacuum leak is a real possibility as well. Since I bought it I have been hooking up stuff here and there, there are unhooked wires and ports everywhere.

The only reason I was thinking of checking the floats is just in case i didn't set them right when I rebuilt it. That is something I have been asked when I first started having this problem and it is something that pops up a lot when looking the symptoms up on line and in books. Believe me I don't really want to take it apart again but just want to eliminate the distributor then the carb as the problem.

 

FIXED! First thanks to y'all for talking me out of buying a new carburetor. I got my new distributor today! I replaced the old one, took it for a spin and problem solved! No more bogging down or dying at WOT, drove better than it ever has. Looking at the old distributor the previous owner must of replaced the cap but the rest was in really bad shape.

Thanks for everyone's advice.