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CarburetorsCarb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
Trying to wrap my engine swap up but on my rebuilt quadrajet the fuel line inlet barb hits this other piece. Just to get things together I plan on using rubber fuel Injection hose until I get the other AN fittings I need. Is there a shorter piece? Here's an attached pic of another quadrajet with the same issue.
I'm not sure what the piece connected to the black hose is but the fuel Inlet won't fit since the hose and the rest of it is in the way.
That part is a vacuum diaphragm. Has 2 functions: it cracks the choke open a bit right immediately after a cold start; and it provides timing for the secondary air valve opening (without it, the AV just kinda flops open or otherwise responds too fast and the engine bogs, stutters, etc.)
Sounds like you need a different combination of parts.
My inlet piece won't even go in since the hose and diaphragm is in the way. Is there an AN fitting that would screw directly into the carb that's also short enough to fit?
QUOTE=sofakingdom;5960012]That part is a vacuum diaphragm. Has 2 functions: it cracks the choke open a bit right immediately after a cold start; and it provides timing for the secondary air valve opening (without it, the AV just kinda flops open or otherwise responds too fast and the engine bogs, stutters, etc.)
Sounds like you need a different combination of parts.
Is there an AN fitting that would screw directly into the carb that's also short enough to fit?
Yup; the one in the pic.
3/8" inverted flare to AN, then a right-angle sweep hose end. There's also an swivel elbow 90 adapter but I like the short straight adapter and sweep better.
I just tried a russells fitting that screws directly into the carb body and it won't even sew in since the end is hitting the diaphragm. The fitting above would stick out farther since it screws into the fitting that then screws into the carb body.
Originally Posted by sofakingdom
Yup; the one in the pic.
3/8" inverted flare to AN, then a right-angle sweep hose end. There's also an swivel elbow 90 adapter but I like the short straight adapter and sweep better.
I'm thinking this aeroquip fitting could work. Turns out there's a whisler bearing industrial supply in town so I'm going to give them a try tomorrow.
Originally Posted by armybyrd
I just tried a russells fitting that screws directly into the carb body and it won't even sew in since the end is hitting the diaphragm. The fitting above would stick out farther since it screws into the fitting that then screws into the carb body.
Something is wrong about that carb. The stock fuel line wouldn't even hook up to that.
Get acoupla pics where all the parts that are involved, aren't all in the dark and deep in the mud, where we can see em; one from in front, one from straight above, one from the pass side. Put a light on the parts we're trying to see instead of on the fuel bowl.
Something is wrong about that carb. The stock fuel line wouldn't even hook up to that.
Get acoupla pics where all the parts that are involved, aren't all in the dark and deep in the mud, where we can see em; one from in front, one from straight above, one from the pass side. Put a light on the parts we're trying to see instead of on the fuel bowl.
I ended up grabbing a quadrajet off of an 82 caddy Deville at the junkyard.
[QUOTE=sofakingdom;5960794]Something is wrong about that carb. The stock fuel line wouldn't even hook up to that.
Get acoupla pics where all the parts that are involved, aren't all in the dark and deep in the mud, where we can see em; one from in front, one from straight above, one from the pass side. Put a light on the pa0rts we're trying to see instead of on the fuel
Like an idiot i bought that first carb off of a supposed carb builder i found on ebay. He asked for all of the engine specs and said everything was rebuilt and tuned to my engine. I'll post a few more pics in hopes of figuring out what's up with that carb so hopefully i can fix it to be used.
You're right not sure what I was thinking. (or even, IF)
Still, it'd be real interesting to have some pics of that other one from the angles I described - straight in front, straight above, and straight from the right, and made under conditions of good lighting in the area in question - to figure out why its vacuum break diaphragm is so far forward.
You're right not sure what I was thinking. (or even, IF)
Still, it'd be real interesting to have some pics of that other one from the angles I described - straight in front, straight above, and straight from the right, and made under conditions of good lighting in the area in question - to figure out why its vacuum break diaphragm is so far forward.
Had me scared for a sec there. Lol before I pulled that carb I was about to have one off of a caprice when I noticed it didn't have an electric choke. :/
Anyways I'll try and get better pics of the old one but the car is in a small one car garage with not so good lighting. In the first corvette fever pic that I posted it also has the fuel inlet pretty close to that diaphragm. Also here's here's a link to the carb rebuilder.
That looks like they used the wrong bracket for the VBD as well as the wrong VBD itself. Looks like it's for an Olds or Buick, where the fuel line comes straight out the front.
Plus, it's all painted black... no telling what that's all about. But it sure isn't how any of it left its factory.
What does it look like from the right side? (pass side; the side it's on)
That looks like they used the wrong bracket for the VBD as well as the wrong VBD itself. Looks like it's for an Olds or Buick, where the fuel line comes straight out the front.
Plus, it's all painted black... no telling what that's all about. But it sure isn't how any of it left its factory.
What does it look like from the right side? (pass side; the side it's on)
Could possibly be... what did it look like when you swapped it?
The VBD is actually a calibration component for the secondary operation, so it might or might not be "The Best". I'm kinda thinking though, the combination of a bracket off of a carb for one of the divisions whose engines required the fuel line to exit straight out the front, plus the link part of the VBD, might be different from one that exited to the side; and the link looks REEEEEEEL long compared to what I'm used to seeing on a Chevy carb. IOW, the whole thing might just simply be WRONG, in that it moves it all too far forward to fit a Chevy carb properly.
A pic from the right side of the carb would help although might still be inconclusive. Maybe a pic of the carb that fits and one of the one that doesn't, to compare, would be better.
It's pretty obvious what's wrong with the black one. It's for an Olds or Buick. Simply, the wrong part for a Chevy. The bracket is clearly wrong, by mounting the diaphragm too far forward, and the VBD plunger piece is too long, since the diaphragm body is too far away from the green link.
If you can depress your LG4 one's plunger and then cover the fitting with your finger and it holds itself in, then it's at least "good" and should "work". The thing is however, the vacuum is fed through a tiny orifice, which is calibrated to provide some particular operating rate of the sec air valve, meaning you might end up with secondaries that open either too fast (bog) or too slow (delay in acceleration when you floor it). Only way to know, is to try it. You can replace it easily enough if it's broken (doesn't hold vacuum) or unsuitable. The "ideal" diaphragm spring and orifice combo is dependent on the vacuum that exists normally right before you stomp on it, and the engine's ability to immediately use more air right after. A great deal of tuning is possible by changing it.
Adjust the screw thing on it so that if the choke is held closed by its stat, and you either apply vacuum to the VBD or just mash it manually, it cracks the choke blade open by about 3/16" or so. Should get it close enough to run OK on a cold startup. You can tune it from there if it either dies shortly after a cold start (too lean... cracks it open too far), or if it seems to load up and labor and maybe even blows out black smoke (too little break).
Last edited by sofakingdom; 09-13-2015 at 01:52 PM.
09-09-2015, 07:54 PM
A few minor detail differences but overall, quite similar.
not sure what I was thinking. (or even, IF)
