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Old 11-20-2003, 05:56 PM
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edelbrock thunder carb

I got edelbrocks new thunder series carb a couple months ago when I did my rebuild. One feature is, it has a "quik tune" secondary air valve to kick in the secondaries early or late. What would be the point of having the 4 barrel punch in early or late??? To me instant response is what would be best. I don't really get the point of this?

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Old 11-20-2003, 06:07 PM
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If you want "instant response", you should've considered a double pumper HOLLEY or DEMON type carburetor...provided your motor combination could even handle the additional fuel and air.
EDELBROCK or CARTER (AFB & AVS) type carburetors are vacuum secondaries for streetability. They open when the engines vacuum signal says open up and let more fuel and air into the mixture. Some motors just can't take the extra volume of fuel and air and never open up completely.
The tuneability of the Thunder series carburetors is to give the owner somewhat more say as to when the secondaries will open up. Give it a chance, it could be the best of both worlds.
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Old 11-20-2003, 06:17 PM
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I'm no carb expert, but if you are getting some stumble when you floor it, it may be because the secondaries are opening too early. That's the point of vacuum secondaries. Some motors can't handle the secondaries opening up at low rpms (I'm not good with carbs, so I don't really know why), so that's the reason for the adjustability of the secondaries. Play with it and see the results...it's the best way to learn.
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Old 11-20-2003, 07:40 PM
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Your carb is the edelbrock version of the carter avs. It is In my opinion the best carb ever made. You could have saved yourself about 350$ by buying an avs on ebay. They are identical. You get your off idle and cruising performance optimized by tuning the primaries by changing rod/jet/acc pump holes etc. You can then tune your secondaries for wot performance by adjusting the air valve so that it opens justy barely slow enough to not get a bog when you really land on it. You can change secondary jets to a larger size, and tune it to open even quicker. They are alot like qjets without all of the complexity. They can be just as responsive as a double pumper if properly tuned without all of the wasted fuel.

Last edited by slyshar2; 11-20-2003 at 07:46 PM.
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Old 11-20-2003, 09:00 PM
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Before I rebuilt the 355 I tuned it out the best i could by using an 02 sensor. It's hard to fine tune it without it. I moved the accelerator pump to the third hole for the longest stroke and ended up leaning the primaries and richening the secondaries. It ran good but always had a "flat" spot when i punched it at a cruise. I tried changing step up springs but that didn't help. It's almost like a split second lean spot but can't be fixed by richening the jets/meters or changing step up springs. It's only momentary too. I'll punch it, then it will go real lean then take off. All in a matter of about a second. I think it's because it's not a double pumper, and therefore not meeting the fuel demand when excessive vacuum is applied. I played around with the secondary air valve but it really didn't do much. That's why I was asking what the actual purpose of it was. Sicne then its had a cam change (more lift and duration) and rebuild. I didn't have much time to mess with it except richen it a little before it went to the body shop. Where she now sits Let me know what you think, thanks guys. Oh yeah its a 650cfm, on an rpm intake, with rpm cam, on a 355 motor.
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Old 11-21-2003, 09:34 AM
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You need to richen your secondary mixture. Try going a step up in secondary jets, and slowly tightening the air valve until that bog goes away. Trust me, it will.
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