28 PCI Carb build question

[racecarguy1968]

Hi
I'm rebuilding a 28 PCI for my FV, I have the new Lybarger Venturi, and I have torn it down and cleaned it, I have removed the choke flap.
My questions:
1) Can you remove or modify the Float chamber vent tube?
2) Can you tap the holes where the choke linkage went through and install bolts to plug the holes? (Obviously not to long as to intrude into the air chamber)
3) I have 2 28PCI's one has an air correction jet in the top half of the carb and the other one just has a hole, whats the difference???
4) the 28PCI that has the ait correction jet in the top half also has a screw to the left of the accelerator pump, the other one I have doesn't have this screw, whats the screw for??

[racecarguy1968]

pictures of the 28pci

[sracing]

Can you remove or modify the Float chamber vent tube?

Nope

2) Can you tap the holes where the choke linkage went through and install bolts to plug the holes? (Obviously not to long as to intrude into the air chamber)

No tapping since that might be considered a mod to the carb. In the pasts protests were made and at the protest it was claimed that NOTHING could go inside the outer shell of the carb. Typically some tape was used to cover the holes. I BELIEVE now that a plug can be inserted (or RTP, etc) as long as it doesn't protrude INTO the bowl.

3) I have 2 28PCI's one has an air correction jet in the top half of the carb and the other one just has a hole, whats the difference???

You are missing the air correction jet and/or emulsion tube and/or emulsion tube holder.

4) the 28PCI that has the ait correction jet in the top half also has a screw to the left of the accelerator pump, the other one I have doesn't have this screw, whats the screw for??

Not sure of where you mean. However if it is really a screw and not an adjuster, it is simply there to plug an open boss that was used for cleanout.

This picture may help:
http://sracing.com/Store/FV_Stuff/REF10.jpg

[veefan]

GCR . Carburetor air cleaner and choke mechanism may be
removed. Choke shaft holes may be plugged. Plugs may
not protrude into the choke bowl.

Most electrical tape works well to cover the holes from the outside except some tape glue is not fuel friendly and will lose its grip over time. I use JB weld to make a plug and seal the holes. Just tape the choke shaft holes closed on the inside, pour in a little JB weld. After its dry, remove the take and make sure it does “ not protrude into the choke bowl”

[Dietmar]

A few comments:

I too do not know exactly what you mean by the screw next to the pump- but I think you are referring to an older (if there is such a thing) model carb that had a screw that held the venturi in place. If you take it out it should have a taper to it. Best guess on what you have described.

On the "jet" and hole on the top half with no jet- I THINK you might be referring to the
discharge "jet" that is built into the top of the carb. Some have screw in jets, others just have a hole. Both work the same.

In your initial satement you said that you removed the butterfly and shaft in the carb top. Does this mean that you have a stock carb and are making mods? If so you need to pay a lot of attention to the throttle plate and the throttle shaft also, not just to the top.

If you need plugs for the carb top, let me know. If you need more info on the carb bottom, also let me know.

Dietmar
www.quixoteracing.com
(619) 647-4728 today
(619) 561 7774 any other time

[sracing]

Yes, He sent me a pictue. He is referring to the throttle pump enrichment jet. The older carbs had a jet (brass) later ones did not. That is fine. The newer ones are metered via a brass tube under a screw above the throttle pump and adjustment of the pump throw. As long as your throttle pump works with a decent spray don't worry about it.

The screw you are referring to is just a gallery plug. It is removed for cleaning and then reinstalled.

[sracing]

I don't want to pee on your efforts, because you are certainly learning a lot. But to get a carb to flow to anywhere near decent specs will take a lot of experience, work and a flow bench. Give it you best shot and bring it down or send it and we will be able to flow it and let you know how good it is and what else could be done. As Dietmar points out, you wlll also have to remove the throttle plate and shaft and size them to the miimum GCR rules. You will also have to modify the screws in the throttle shaft so that they don't protrude into the flow. (heads and threaded ends) We have biult dozens of them and it is an all day job WITH a flow bench, and then it has to be jetted on the dyno. That is why they are so expensive.

(BTW, USUALLY, but not always the carbs with the brass jet in the fuel enrichment boss flowed a bit better.