I bought this remanufactured Edelbrock Thunder AVS 650 CFM carb from Summit Racing. The motor is a new mildly built 350 with about 2000 miles. Runs great except when I give enough throttle for the secondaries to open -the motor falls flat on its face. It goes so lean that it feels like I'm letting off on the throttle. It will never recover unless I ease off the secondaries. RPM or speed make no difference. EDIT: Richer secondary jets have no effect.

Today I took the airhorn off for the first time and saw what seemed to be old fuel in these two areas. (dark, less-strong smelling fuel) I can identify most components inside the carb but im not sure what these are. They are circled in red;

 

clean it out, spec it, and make sure no parts are missing, then what size fuel line ? how much volume and pressure do you have?

 

Cleaned it out, no parts seem to be missing. Stock fuel line into larger braided steel. Regulator set to 6.5PSI, its an externally mounted electric pump. I learned that those two areas with fuel in them are part of the secondary transient system and the "old" fuel was just distilled from heat soak.

My secondary bog is now the least of my problems. I was changing out jets and adjusting the air valve and after this one WOT pull the motor ran like crap. After cleaning out the circuits a few times it idles normally now but it is very LEAN in all operation conditions. The idle adjustment screws are now very touchy-- a half a turn in either direction will cause the idle to drop--wasn't like this before. The carb ran just fine before so something isn't right. Floats are correct, rods installed correctly, no vacuum leaks. And I heard Eddys are good for daily drivers....

 

Make sure your squirters are squirting fuel when you press the gas down. Pull the accelerator squirter and make sure the ball moves. I have seen a lot of people forget that on the rebuild.

Also tune the idle screws with a vac gauge.

Check for vac leaks

Those holes are where the weights for the air valve sit. Are you missing it?

#42 on page 34
http://www.edelbrock.com/automotive_...406_manual.pdf

 

Well I double checked the rods and turns out I forgot to put the stock rods back in when I changed everything back to stock. LOL I feel stupid. Runs perfect now except the secondaries bog from before.

This is a Thunder AVS series carb, so IIRC it won't have weights-- instead it uses the adjustable spring pressure for valve actuation.

Thanks for the replies guys. I still wonder what this secondaries bog is all about... I wonder if it's my 6 x 1.5" air cleaner LOL

 

Does the bog happen when you mash the gas? Does it go away when you slowly go to WOT?

 

I should rephrase what I said, it isn't just a WOT bog. It happens whenever I give it enough throttle for the secondaries to operate. It happens when I mash it and when I ease into it. From a complete stop and from 4k RPMs, it happens under all conditions.

 

Did the carb have the problem right out of the box?
Those rebuilt carbs are just the warranted carbs that were taken in and rebuilt and resold. If there is a machining defect in the carb or something like that they will never know because they can't test the carb. They just rebuild it and resell it as reman.

 

Yep right out of the box.

 

Have you tried adjusting your secondaries? Usually bogs like that I have fixed by making the secondaries open a bit slower.

 

Sounds like the same problem I had with my Q-jet carb. Anything past ~1/2 pedal and the motor would bog. I checked out my carb and the secondaries were not opening at all. I'd guess your secondaries are not opening.

Now with mine it was a piece missing on the choke not hitting a lock out lever keeping the secondaries closed. With Holley carbs you can put a paper clip on the vacuum rod and see if the secondaries open. I'm not sure how you could verify if the secondaries on the Edelbrock carb is working. I haven't messed with one over 20 years ago so I can't remember all the things pertaining to them.

 

Last night I had more time to fiddle with the air valve adjustment as well as secondary jets and I was able to get a small improvement. Maybe it is just fine tuning after all...

I had figured that such an issue as I'm experiencing could only be some sort of defect/broken part or installation mistake and not simply a matter of fine tuning.

I REALLY appreciate all the advice and replies. Thanks! I'll let you know when I get it straightened out.

 

Just an FYI

I looked at my Edelbrock that is sitting on my work bench and it has a secondary lockout similar to the Q-Jet but on the Edelbrock carb the lockout is on the throttle lever side. I held the choke open and the secondaries would open and with it closed the secondaries would not open. Although, because this carb is needing a good cleaning the lockout lever would not always move and keep the secondaries from opening. These linkages need to be kept clean to work properly so don't forget to check these out once in awhile

 

don't know much about carbs, but on the 750 DP it'll do that if one of the power valves is blown....