Carter BBD confusion

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glhx

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I had the holley 2280 2 barrel on my 318. Started leaking around the throttle shafts. i decided to replace it with the carter bbd low top.

Funny thing i noticed about this carburetor is that the fuel pump diaphragm has a spring on the top and the bottom. so when i got the carburetor the throttle blades are always open. Upon installation i will have the throttle return spring on there and it will pull the throttle closed. if the spring ever happened to break or come off , the throttle would open to full throttle and make the car suddenly accelerate. I just dont like the idea of this.

so why was is designed this way and can i take the top spring (that is pushing the diaphragm down) out of there so the throttle blades are closed when the throttle return spring is off. google images will show pics of this carb in the wide open position. ive never seen a card do this....they always came out of the box with the throttle blades closed
 
??? That doesn't sound right. Where did you get this Carter?

You say "Funny thing i noticed about this carburetor is that the fuel pump diaphragm has a spring on the top and the bottom." I assume you're referring to the accelerator pump. I've had mine apart, it only has a spring at the top.

The throttle blades are closed on mine, the throttle return spring keeps it that way. Almost sounds like you got a carb someone's been messing with and got it installed backwards!

Here's some pics of mine on a 273, hope it helps.

Barracuda 052 (2).jpg


Barracuda 053 (2).jpg


Barracuda 054 (2).jpg
 
Yes, they open, or a better description would be that the blades relax open. I don't think the throttle shuts by itself with any internal spring.

Your statement: "Upon installation i will have the throttle return spring on there and it will pull the throttle closed. if the spring ever happened to break or come off , the throttle would open to full throttle and make the car suddenly accelerate." is correct. However, the likelihood of that happening is pretty remote. If you want to be extra cautious, you should buy a new spring, or you could always rig up a second return spring in case the first one fails (an old racer's safety trick, but this will put extra tension on your accelerator cable).

I gotta fiddle with it tomorrow, if I spot this thread open afterwards, I get back at you.
 
in thinking about this. a carburetor that stayed closed and would not relax open would have the same problem. you would be pressing on the gas pedal and it would fall to the floor. you would turn off the car or pull the pedal back with you foot if you could. only time it would ever be a problem is if the car were idling and you ran into the store. the spring would breake or come of and the throttle would relax. then the rpms would raise wide open and could possibly blow up the motor. it is a long shot but damn ive seen some stuff happen.
maybe that spring on top of the diaphragm should have been just placed on the bottom of it pushing the diaphragm up instead. i have not had mine apart yet. but the exploded view shows 2 springs. one on bottom and one on top. i wonder if the carburetor actually does have one on the bottom. and i wonder if if doesnt....could it be put there instead of the top.
 
This IS confusing...I have a bbd from a slant that has a spring on the throttle blade shaft between the linkage and the lower body... even with the carb sitting on the shelf ( relaxed ) the blades are closed by that spring.

carter return spring.JPG
 
i have a 68 carburetor. you may have a later design when the company had some common sense. check out this cool dual 2 setup with carter bbd's

318engine.jpg
 
It's been a long time since I had my 67 Plymouth Fury, but I can assert that this is exactly what could happen. I was on the freeway in heavy noon traffic when my throttle stuck wide open. No good place to pull over at the time either, so putting it in neutral and then shutting it down wasn't that good an option. I ended up really standing on the brakes, which just barely managed to keep that beast under 65. Found the nearest off ramp and got off the freeway, sweating like a pig.

At the time, I was able to make temporary repairs with some other spring that I could find, but I was unable to find the proper replacement. Fortunately, I was able to get another car and got rid of that mess.

Sucky.
 
It's been a long time since I had my 67 Plymouth Fury, but I can assert that this is exactly what could happen. I was on the freeway in heavy noon traffic when my throttle stuck wide open. No good place to pull over at the time either, so putting it in neutral and then shutting it down wasn't that good an option. I ended up really standing on the brakes, which just barely managed to keep that beast under 65. Found the nearest off ramp and got off the freeway, sweating like a pig.

At the time, I was able to make temporary repairs with some other spring that I could find, but I was unable to find the proper replacement. Fortunately, I was able to get another car and got rid of that mess.

Sucky.
 
This IS confusing...I have a bbd from a slant that has a spring on the throttle blade shaft between the linkage and the lower body... even with the carb sitting on the shelf ( relaxed ) the blades are closed by that spring.

That's a 2280 Holley...I can tell by the shape of the bowl.
 
1974 was the first year Federal regulations required a redundant double throttle return spring setup so that one spring could fail and the throttle would still close. That's why '74 and later carbs have a built-in throttle return spring but the '74-up cars still have the separate bracket-style throttle return spring. The most common way of retrofitting this easy, common-sense safety feature to an earlier car is to fetch a large-diameter regular pull-style coil spring with hook ends, just like the original throttle spring but larger in diameter. Place the original small-diameter spring (or its new replacement) inside the large-diameter spring. Hook both springs to the bracket and to the throttle lever. Voila…dual redundant throttle springs.

And no, you cannot remove the accelerator pump plunger spring and expect the carburetor to work correctly. It won't.
 
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