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Rochester 4GC carburetor question


West Peterson
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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.

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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?

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Screen Shot 2021-02-18 at 2.54.47 PM.png

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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.

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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.

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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 by carbking (see edit history)
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(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.

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