The Stovebolt Site Forums The Shop Area Engine Shop Another Carter YF2100S question

Hello Guys,
I've read and read and read but hoping for some guidance. Carter YF2100S on my 59 3100 w/235:
Rebuilt the carb, running nice until shut down then the "Main Jet" (at the top of carb bowl inside upper venturi) dribbles gas ontop throttle plate causing leaking down shaft, etc. You can see the gas fog lifting out the top. Even started doing at idle today? I have studied the carb for hours/days, and I'm wondering:
The base of the carb (cast iron base) has two(2) holes. The gasket covers one and has a cutout for the other (the one that is directly underneath the idle mixture screw). The other hole travels through the base, into a open section underneath the base of the carb body. In this open cavity, there is a small hole intersecting the "well" that the accel pump diaphragm sits on. Seems to me that passage should be under manifold vacuum to suck the diaphragm down? But the gasket prohibits this? The diaphragm while under idle vacuum would pull down whilst pulling the metering rod down to its more restricted position?
I hope this makes sense as this is driving me crazy, lol!!!

If you could grab a picture that would be great. I’d have to go study a diagram of the circuits to fully understand what’s going on there. The hole you’re referring to may or may not have anything to do with the symptom you describe.

That said, my rule of thumb is always: “If there’s a hole, make sure the gasket doesn’t block it.” You should be able to punch/cut a slot in your base gasket so the hole you’re referring to sees vacuum.

I have found that base gaskets are a crapshoot on any number of carbs I’ve worked on. “One size fits none” type of stuff.

Here are a couple of thoughts:

1. in the 2100S the only vacuum tube runs up to the bottom side of the well below the diaphragm (and there also may be a tiny vacuum bleed hole running off to the inside of the carburetor bore). It is very important to make certain the bonnet which holds the diaphragm down is completely flat. Somewhere here I have shown how to use a couple of pieces of sandpaper and a flat piece of wood with a 1 1/4" hole drilled into it to correct the warping you will find in some of these. If this isn't done and if you have a leak at the point where the diaphragm meets the float bowl, raw gas will be sucked into the manifold while the engine is running and raw gas will actually leak past the diaphragm and will dribble down out of the well when the engine is cut off. Plain old gravity will take care of this. You will see wetness from gas at the seam (gasket) where the float bowl meets the throttle body and also you will see it on the throttle valve and the shaft of that valve. It is critically important you never get gasoline into that well as nothing good can follow if that happens.

2. we have no idea where you got your rebuilding kit. It may have been one with an incorrect needle and seat. If so, you probably are allowing too much fuel into the float bowl. Carter engineers spent lots of time/effort designing these and they had instruments we (and the people selling the imitation kits) will never have. The "generic" kits out there may have a seat with a very large opening. It should not cause fuel to run into the engine after you turn it off, but if you have a problem there

3. the float adjustment is also very important...but it assumes you have the proper needle and seat.

4. make certain you have a fuel pump that is only providing at the absolute most about 4 psi. Preferably 3 psi. These engines and these carburetors do not need more than that. If your fuel pump is providing something like 10 psi, that's likely to force fuel past your needle/seat and into your float bowl.

Hopefully some of that is helpful.

Here is a link to that post I mentioned:

https://www.stovebolt.com/ubbthreads/ubbthreads.php/topics/1442663/1

I will take and post some pics shortly. Thanks guys

Sorry about the crude drawing of the gasket but it is the standard style with the four cutouts. Note that these gaskets only one of the bottom ports to be exposed.
Upon further inspection, it appears that both the base holes travel up to the base of the carb into a chamber. This chamber has one small hole that penetrates the throttle bore while the other has a larger hole that enters the accelerator pump bore (which sucks the diaphragm down and holds it). Gasket covers one yet they purposely engineered two. Some report cutting the gasket for the second port which in theory would provide a steady vacuum?
I was under the assumption that once the accelerator pump was pulled down that the metering rod would also come lower therefore restricting low idle flow. As I push the diaphragm down the metering rod doesn’t come with it. Rather the metering rod appears to rest at its lowest point then mechanically comes up once the throttle moves (thus opening the lower jet allowing more fuel.
At idle, which the throttle plate totally closed, I’m getting a slow drip from the main jet. Which continues to drip after shutdown. Then fuel accumulates and travels out the base of the throttle plate rod, etc.
Note the carb base to throttle body base gasket also has two holes for the vacuum to travel.

BTW- regarding that small hole from the vacuum chamber to accelerator pump well that goes into the bowl bore, what does that do? Seems that would also provide some small ported vacuum?

Lastly, should I pull the carb back off and provide a route for the other covered hole? Couldn’t hurt!?
And if so, is the slot in the gasket enough or should the carb heat insulator be milled alittle also. I notice the the insulator has two milled slots but neither lines up with the Carter Carb or the gasket. Maybe they were always designed for the Rochester B. Thanks for the ranting guys, I’m neck deep trying to solve this. Don’t want a fire in my two year project.

Engine idles and runs fine btw. Just the leaking fuel issue

First, where did you buy your rebuild kit?

If it didn't come from carbking (Jon H) / The Carburetor Shop, there may be missing or incorrect parts. It's also possible that your YF is a cobbled together frankencarb sold by auto parts stores as a Fitzall when in reality it fits none.

Contact carbking with all the numbers on your carburetor and the numbers on the metering rod. He'll make sure you're starting off with the correct carb for your engine and see to it you have the right internal parts.

He's a member of this site and can be contacted via PM. carbking

Jon H
The Carburetor Shop
573-392-7378 (8:00-5:00 Mon-Tue)

Carb was bought from a guy who said he “rebuilt” it. Unknown who’s Kit. Spoke w/John on phone. Have measured all the components based off an old post from John C., who provided specific measurements. All parts measured out correctly. I have a second YF2100S i found Have verified that all the parts are installed, have tore down measured, cleaned (both w/ carb cleaner pushing through offices and a dip in the untraditional ceaner). Re-double check float level, etc.
Does in fact run and accelerate properly, just the flooding at idl(low idle) and after a shutdown the main jet drips. Also rebuilt orig A/C fuel pumps my stor brought was pushing over 20psi (which was suggestions from John). Rebuilt pump checked at 4 psi. Needle/float cannot be over riding by blowing w/ mouth pressure. When I lift the top cover off, fuel is resting about half way in resivour. Which seems correct ( not over full approx 1” down from top).

Just FYI. Blowing with mouth pressure won't overflow anything. Humans can produce no more than about 2psi from their lungs, which is right in spec with a Carter YF.

Perhaps the leaking is coming from the accelerator pump?

Here’s the gasket and heat insulator. Insulator has port relief consistant with original Rochester B. Gasket with kit only lines up with the port that’s on the side of idle fuel screw. The other is plugged from gasket. So it seems that both the gasket AND the insulator needs a slot to both openings? My thinking is that Carter seem to know what they were doing and the gasket manufacturers today aren’t providing the correct gasket and insulator for the Carter!!??
Hope this is making sense. All of you that have commented are sharpe guys as I’ve read your responses over the years. I baffled. By the way I’ve got about a 1/4” of raw fuel sitting inside my intake manifold right now after my start up yesterday. Ughhhh

When I've had dribbling and pooling of fuel on the intake runner in the past, the culprit has always been a faulty accelerator pump. Usually that's accompanied by a performance problem which you don't have.

Still, I'd look closely at the accelerator pump assembly.

I will. The drip is defiantly coming from the High-Speed Circuit (tip of nozzle, in the center of the bore, near the top of the opening).

John G- I read your previous post you referred me too and I must say it is excellent. Absolutely makes me think and hope it is my problem. Symptomology is consistent for sure. Curious though, it seems my rubber bonnet on the bottom of the accelerator pump is attached? Can I remove it without some type of damage? I didn't want to pull it too hard.

Worst case scenario, you can buy a new accelerator pump diaphragm without buying a whole new kit.

If it’s stuck to the metal part you might tear it, but it’s not the end of the world. Just don’t be a meathead about it and damage the metal surface.