GM carb'd 2.8 tuning??

I have a 84 Chevy S10 with a carbuerated 2.8. I have been having issues with getting it to run well.

When I get into the secondary it will stumble and seems to backfire and run poorly before it starts to move faster.

I was hoping it was just due to a air fuel ratio problem but it looks like when I get into the secondary it runs between 12 and 13:1 and from what I understand that is good?

Im assuming I may be having vacuum problems. When I get into the secondary the vacumm drops down low. Im not sure what the measurements are on the guage but one side sais between 5 and 10 and the other is around 100 and 200.

Can anyone please help me :CRY:

Im not sure what carb it is past it being a stock rebuilt carb.

How do I check the EGR valve?

take the egr off its got a diaphram inside see if the diaphram is torn or anything, its probably plugged up, if thats the case give it a good blast thru with brake cleaner