Rochester 4GC carburetor question

[West Peterson]

I'm looking for a couple of choke thermostats for two Rochestrer 4GC carburetors. Any idea where I can get a pair of these?

[joe_padavano]

Many of the carb specialty vendors sell these. Here's one source. $20 new.

Here's another.

 

 

[carbking]

It would not seem to be the case, but there are MANY DIFFERENT of these things.

 

New old stock is best, and probably quite expensive if you find the correct one.

 

Good used is second best, and somewhat less expensive, if you can find the correct one.

 

Repairing what you have would be the next choice.

 

The brand new powder cast versions have no rigidity, and will not hold up, other than as paperweights.

 

Both of the ones you picture are fixable.

 

Jon.

[deaddds]

If you have the carb info I can check my nos stock. Drop me a line at dead@mchsi.com.  Cheers

[West Peterson]

2 hours ago, carbking said:

It would not seem to be the case, but there are MANY DIFFERENT of these things.

New old stock is best, and probably quite expensive if you find the correct one.

Good used is second best, and somewhat less expensive, if you can find the correct one.

Repairing what you have would be the next choice.

The brand new powder cast versions have no rigidity, and will not hold up, other than as paperweights.

Both of the ones you picture are fixable.

Jon.

 

Thanks for the information, Jon.

What are the differences? You state there are many different ones... I have found a good used one and a NOS on Ebay, so how do I know if they'll work for my 1955 Packard Caribbean?

[carbking]

West - check the "rich - lean" direction arrows to start with; then check that the inside "slot" is "clocked" the same as yours. Of course, you can always ignore the original setting by number of bars, and just set the choke, but if trying to keep original, then clocking is important.

 

There are other differences in the lettering that probably is no longer important, but I have had some very "intense" customers over the years.

 

The springs also have a different coil length to control the timing, but again, one can generally adjust for this.

 

Automatic chokes were one of the "cash cows" for the carburetor companies. Change the clocking 2 or 3 degrees, change the part number each year; and EVERY dealer would order 2 of each at the beginning of the model year!

 

Jon.

[West Peterson]

3 minutes ago, carbking said:

Automatic chokes were one of the "cash cows" for the carburetor companies. Change the clocking 2 or 3 degrees, change the part number each year; and EVERY dealer would order 2 of each at the beginning of the model year!

 

Jon.

 

!!!! No wonder I have so many questions. It sounds like they'll all fit, but will have to be adjusted accordingly. Do I understand correctly.

[padgett]

And make sure the metal spiral goes the same way.

[carbking]

No, they won't all fit, but most of the ones with the male fitting on the outside of the choke will fit, and can generally be adjusted to work.

 

Jon.

[West Peterson]

Here's the inside of one of mine, and apparently the "tab" that holds the spring isn't even there.

[West Peterson]

1 minute ago, padgett said:

And make sure the metal spiral goes the same way.

 

Yes. I see that some go one way and some go the other, but all you have to do is flip the spring.

[carbking]

3 minutes ago, padgett said:

And make sure the metal spiral goes the same way.

Also, make certain, the spring is activated by heat the same way.

 

Have not tested all of the Rochester chokes, but Carter made some that were wound the same way; but uncoiled in opposite directions when heat was applied.

 

Jon.

Edited February 18, 2021 by carbking (see edit history)

[padgett]

But some springs can be reversed.

 

Meanwhile needing two 4GC chokes makes me think of all of those neat dual quad GM engines of the 50's.

[West Peterson]

7 minutes ago, padgett said:

But some springs can be reversed.

 

Meanwhile needing two 4GC chokes makes me think of all of those neat dual quad GM engines of the 50's.

 

This is for the dual-quad set-up in our 1955 Packard Caribbean.

[padgett]

Yes Rochester sold to a lot of companies. So did Delco.

[West Peterson]

3 hours ago, carbking said:

Both of the ones you picture are fixable.

Jon.

 

Nothing left of the male portions... no threads. How do you fix that?

[carbking]

(1) Mill the remaining projection from the outside of the choke cover

(2) Machine a custom brass fitting on your lathe. The fitting should have the correct male thread on one end, and a small shoulder to fit against the outside of the choke cover. On the inside of the shoulder, the fitting is tapped to thread into the choke cover. The fitting should have approximately the same inner diameter as the original. The very inside end  should be milled on either side to have a slot that will hold the spring. The threads that thread into choke cover should be approximately 1/8 inch too long (standing proud of the cover on the inside by 1/8 inch).

(3) Tap the choke cover for the same thread as you used on the fitting

(4) Machine a brass nut 1/8 inch thick with the same thread.

(5) Assemble the fitting into the cover, and secure with the nut.

(6) Re-install the spring

(7) Re-install the cover on the carburetor.

 

The inner clocking will be off; although this can be corrected by only threading the last 1/8 inch going through the cover, rotating the fitting until the correct clocking is obtained, and then secure with the nut. I prefer to have the cover threaded.

 

Some items are made of unobtainium or verypricium and must be fabricated. If you found two on ebay, then this item made not be one that deserves this amount of fabrication.

 

Jon.