How do I check if the back barrels of my carb are working?

Question

I have Chevy 355 w/ a quadrajet carb. I've been told that some of my vacuums & back barrels arn't working. I have and edelbrock 600cfm getting shipped to me but just out of curiosity how much more power do you think I can get from the new carb compared to the carb w/ the broken back barrels? How do I check if the back barrels are actually opening all the way when im at WOT?

Answer 1

Back barrels don't just break niether do front. You need to check your idle jets and make sure they are clear and not plugged up. also all main metering jets front and rear has to be clear with proper float adjustment. If rear barrels are vacum controlled you will have to check the vacum pull off or secondary linkage. To check all barrels you take a timming light and point it strait down each barrel a give the carb a quick punch to the floor while looking down the barrel you should see an even amount of gas around the input barrel with the light. Remember even at full throtlle your adle jets must be working. So for full fuel tighten down on them until they seat then back off three turns to each one of them, then start turning them until you reach you highest RPM reading on you meter. You will have to do this with your new carb.

Sincerely yours,
Fred M. Hunter
[e-mail]

Answer 2

The motor can be off. Just take the air cleaner off and grab the throttle (where it's hooked up to the accelerator cable) and rock it back as if accelerating and look down the barrels. You will see the "flaps" begin to move and see gasoline squirt in and the top and bottom "flaps" or plates will open the further back you rock the throttle.

You can mimic this with a new carburetor right out of the box minus the gasoline squirt.

Answer 3

with it idling and the breather off of it gas it once and see if it try's to open up you,ll see if the top flap starts to move on it,and you can also check the vacuum part of it with a vacuum pump to see if it opens it up,and the engine doesn't have to be running to do this,but usually those are good carbs,and don't give many problems the new ones didn't open up as good as the older ones did,but there still a good carb,try that and see if it helps any with it,good luck with the edelbrock also, i own a 600 on my Chevy,it does ok.

Answer 4

Disconnect them, drive it, reconnect them, drive it, did it have the effect you expected?

I suppose you could stick a light and a webcam in there or something too...