Poor Fuel Mileage on 4.3 V6 with Quadrajet 17056250

[Cliff Ruggles]

Are you saying that you swapped baseplates during the rebuild using one from another carburetor part number?....

[don3194]

Well I think so, I don’t know what number it came off of.
 I swapped it because I discovered that the one from the 17059222 was actually cracked around the primary shaft and very worn out on the secondary shaft. I thought I could just try it and hope those holes didn’t make a difference. I don’t think it did, but obviously it’s developed a vacuum leak somewhere and it could be related.

[Cliff Ruggles]

It's supposed to be loose on the secondary side as the large throttle plates need some room to seal in the bores each time they close.

A crack means it was dropped at some point and doesn't hurt anything.  Using my bushing install kit you can bore in deeper to install a bushing.  I've done hundreds of them that were cracked and even had a chunk missing out of them.

In most cases the shaft is also bent and will need a little "tweaking" after the bushings are installed....

[don3194]

When I say loose, I mean that the secondary shaft moves enough so the throttle plates will actually stick in the bores until the primaries reach wide open throttle, then they fly open.

[don3194]

Upon some inspection I noticed that the gasket is not sealing the the middle, I can see where the gasket has been crushed in most of the areas but right in the center I can see where the air is seeping passed. Its right in-between the two primary bores. The gasket has no witness marks of being crushed but lines where I could see the air. I’m not too sure how to resolve this issue but neither baseplate seals it.

[Cliff Ruggles]

Not possible unless someone put too much "monkey chit" (JB Weld or other useless epoxy for sealing up bottom plugs) on them to push the two parts away from each other.  The main casting to baseplate gaskets are really thick and will seal up those parts without much effort.

I actually see that a LOT with carbs that come in here with those issues, either too much glue or the plugs they installed are too high.  Most carburetors built after 1968 do not leak, but for some reason EVERYONE gobs tons of JB Weld over them, which woln't hold back fuel right to start with.....FWIW......

[don3194]

Actually there is no epoxy or glue or anything on the plugs, which is why I'm confused too.

[don3194]

I really didnt want to have to do this, but I think I will just re-bush the original baseplate. How much do your kits cost?

Unfortunately I think I need to do both the primary and secondary shaft bores.

[Cliff Ruggles]

I'd leave the secondary alone.  They seal tight on the large throttle plates and need a little room at the shaft to settle in each time they close.

You can order the primary shaft kit right off the website or call me at the shop, I'm here 7am-4pm, M-F EST...tks...

https://cliffshighperformance.com/product/5-16-throttle-shaft-bushing-kit

[don3194]

Okay thanks, I’ll see how it works out after the primaries have the bushings. The fact that the secondaries were sticking in the bores worries me but I guess we’ll see.

[tayto]

try adjusting the secondary throttle plates and/or checking to make sure the shaft isn't bent. make sure to grind the ends of the screws off so they don't snap off

[Kenth]

The throttle blades are bevelled so they wont stick.
I have seen "frankencarbs" with blades installed upside down sticking.

[don3194]

Hmmm ok, well unfortunately I took it apart before I read this I so I guess I can't tell if that was the problem.
I am, however, unfortunate enough to have had the baseplate taken apart before (god knows why, they didn't even install bushings) and one of the screwholes is no longer a 3-48 sized hole. The threads are completely gone. Is it ok to resize it for a 4-40? Otherwise I'm kinda stuck.

[Cliff Ruggles]

Go to 6-32 threads.  I supply 6-32 screws with the bushing install kits for that reason.  You'll also have to open up the holes in the throttle plates slightly for the larger diameter screws......

[don3194]

Oh ok, I didn't know you supplied a larger size. I guess I feel better having even larger screws that 4-40 anyways.