The Stovebolt Site Forums The Shop Area Engine Shop Carb to manifold gasket ... ?

Can you reuse the carburetor to manifold gasket from a Rochester B when switching out to a Carter YF, or are the vacuum/idle circuit holes located differently?

Asking for a friend who is having idling issues because he did not use the gasket that came with the YF and wants to know this before removing the YF ... which is a minor PITA ...

Make sure that any vacuum passages in the carburetor flange aren't blocked, and that there's no way for outside air to get drawn into the manifold. There's nothing particularly magical about gaskets- - - -I've made dozens of them with nothing but an X-Acto knife and a few brass cartridge cases for hole punches.
Jerry

John. I don’t think your question can be answered without pulling the carb. Going from a very fuzzy memory, I do think the vac passage in MY Carter is clocked in a slightly different position than the Rochester.

There are a few different versions of the base gasket. The one often supplied is multi-slot affair with a few different options. I do think that one will work on either carb, but if you don’t recall what your gasket looks like᠁you better just “embrace the suck” and unbolt your carb.

I have seen 2 different locations for the vacuum signal passage on model "B" carbs.

Will definitely run rich / poor mileage if passage is blocked.

When adapting ANY donor carburetor to anything it is wise to ALWAYS (and you know how I detest that word!) use the gasket for the carburetor under the carburetor.

It is sometimes necessary to use a second gasket to seal the intake manifold.

The correct Carter YF gasket has slots that will allow intake manifold vacuum to the passages that need vacuum. SOME of the YF's have an access hole cut in the throttle body that goes nowhere. So check the passages, but use the Carter gasket, not the Rochester.

Jon

Here’s a Carter yf 2100s and two Rochester was told one is for a 216 and a 261 ??? Maybe these will be some help.

Well... come to find out, after pulling the carburetor, I DID use the right gasket. Nothing was blocked.

Next step is to rebuild the carb once Carbking's kit arrives. Hopefully the issue is in the idle circuit and a good cleaning and rebuilt will correct the naughtiness of this unit.

In the meantime, I'll set the idle high and go back to woodworking. :-)

Did you ever sell that table saw you had posted some months ago?

Joh,
Is your engine running rich? YFs have an accelerator pump diaphragm which is prone to developing holes in them. This causes a slightly rich condition until the hole opens up later, then its really rich. Not a big problem in terms of making it back home. All you need to do is pull on the throttle cable to keep the throttle open enough to burn the excess gas at stop lights. Found that out one day.

Jon G -- Yes, I did.

Thanks Carl. I think that's essentially what I'm doing with setting the idle higher.

Carl - I tore my YF apart yesterday to replace pump diaphragm. It exhibited symptoms of a faulty diaphragm, but nothing I was able to visually SEE during inspection. When you speak of pin holes, are you able to see them?

I replaced it anyway, and I can’t seem to replicate the flooded hot start condition it had developed. I guess it must have helped.

Truck still isn’t performing quite up to its usual standards. I did check dwell (was good at 28-29) ran out of daylight before I could do any more diagnoses. It runs like it needs more timing. Maybe the dizzy slipped somehow. I’d find that weird but possible, I suppose.

A few years ago (while doing the work on straightening the Rochester B carburetors) I set out to find anything else that may have been warped or not flat and I discovered the bonnet piece that sits atop the diaphragm in the YF can be warped. If this is the case (and the one I used for the example was warped by .008" on one side and .006" on the adjacent side) what happens is the ever-present vacuum that regulates the diaphragm/metering rod assembly will suck raw fuel right into the manifold. In other words, the chamber loses the air-tight nature it needs to work and two things happen: 1---there isn't enough vacuum to hold the metering rod down so it moves upward into the area where it allows more fuel through the main jet and 2---it sucks fuel through and into the engine. Makes for a rich situation. There was a gasket developed to help remedy this but Jon H doesn't use it, feels it worsens the situation and I agree.

So using a flat piece of wood and some sandpaper I "machined" the casting to correct this. Some of the images of what I did below.

Jon-

Good call out, I did check my bonnet when I rebuilt the carb a couple years ago…..based on your work. Mine was still true enough that I couldn’t get a feeler gauge underneath it.

Good! A way I discovered to know if this is happening in your YF is to look at the gasket between the throttle body and the float bowl. If gas is getting by this junction, that gasket will look damp on the edge as gas will dribble down and saturate it. Image below for anyone interested.

Edit...two more images showing the path of vacuum to the diaphragm chamber and you can see why the gasket will be wet if this seal fails.

If you stretch the rubber diaphragm, the pin hole may show itself.

If you stretch it enough, the hole will be REALLY BIG.

And if the diaphragm is leaking, it will have the same effect as my last post above...gas will run into the area between the float bowl and throttle body and you'll see a damp gasket edge where the little red arrows point...

I should have paid closer attention before I tore the carb apart….to that gasket/parting line.

It can be a clue.