1970 Rochester Carburator

[Terry B.]

Re: 1970 Rochester Carburator

Terry, Thanks for the clarification, I'll give it a try

[Terry B.]

Re: 1970 Rochester Carburator

Jim, my understanding is that only the 1970 4 speeds came with the dashpot

[Terry B.]

Re: 1970 Rochester Carburator

I've tried a new return spring and that helped a little but not enough to return the idle speed fully to 750rpm. Maybe a slightly stiffer spring would do the trick if i could find one that fits.

[Jim T.]

Re: 1970 Rochester Carburator

Terry did the Holley equipped 1970's with 4-speeds as well as the QJet equipped 4-speeds come with the dashpot?

[Terry B.]

Re: 1970 Rochester Carburator

Jim, Only the LT1's in 1970 came with a Holley and to my knowledge, they did not have the dashpot

[Terry M.]

Re: 1970 Rochester Carburator

Jim, my understanding is that only the 1970 4 speeds came with the dashpot

In 1970 ALL Corvette Rochesters, BB & SB, manual and auto, came originally with that dashpot. Note the picture I posted was of a small block M40.

[David L.]

Re: 1970 Rochester Carburator

In 1970 ALL Corvette Rochesters, BB & SB, manual and auto, came originally with that dashpot. Note the picture I posted was of a small block M40.

Terry,

I have my doubts that all 1970 Corvette Quadrajet 4-BBL carbs, both SB & BB, came with the dash pot but, of course, anything is possible on the assembly line or at the Chevrolet dealerships. The part number of the dashpot is 7038765. One sold on Ebay last May (see photo below and Ebay auction # 350567855631).

According to my Delco Rochester Bulletins 9C-170 and 9C-171 (in link below, on 2nd page of each bulletin) dated December 1969 the only 1970 Quadrajet 4BBL carbs that had the 7038765 dash pots are as follows: 7040201, 7040501, 7040203, 7040503, 7040205, 7040505, 7040207, and 7040507. These would be models with manual transmissions. I realize that this is only vintage documentation and not physical evidence.

The only physical evidence that I have is a one owner 1970 Camaro SS350 w/Muncie with it's original 7040213 Carter Quadrajet and no dash pot which checks out the bulletins. The "early" 1970 Camaro SS350 models w/Muncie were issued the 7040203 carb.

I have two 7040203 Quadrajets, one Rochester dated "2619" and one Carter dated "A0". Both do not have the dash pot but I bought them at swap meets back in the early 1990's and anything can change in 20 years.

Dave

http://imgur.com/a/FH7TR#0

http://www.ebay.com/itm/NOS-1970-CHEVROLET-CHEVELLE-CAMARO-NOVA-ROCHESTER-4BBL-SLOW-IDEL-DASHPOT-7038765-/350567855631?ru=http://www.ebay.com/sch/i.html?_sacat=0&_from=R40&_nkw=350567855631&_rdc=1&nma=true&si=kBI7cr4uwc7LxkMAP9L%2BNQ03VIw%3D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557

[Terry M.]

Re: 1970 Rochester Carburator

Very interesting documentation Dave. From a functional standpoint I can see where that dashpot may not have been necessary with the M40. I am going to have to go back over my notes and look again at what I have observed over the years.

[Joe L.]

Re: 1970 Rochester Carburator

All------


Also, while we know these things were used on 1970 Corvette Q-Jets, I can't find that they were ever cataloged in the Corvette P&A catalogs for any application.

[Bill L.]

Re: 1970 Rochester Carburator

I have a 70 L46 with original carb. We installed bushings and still had a slight problem. Does it move freely without the accelerator cable attached? Sometimes the bracket and or cable can be off a bit or the bracket can be bent and cause the problem. I just had to make sure the accelerator cable was securely attached properly and it gave me the 1/32-1/16 i needed to dial in the idle.

The other problem I have experienced with Qjets is that it may appear that you run out of idle adjustment with the screw or dashpot (70 only) when it turns out that either the timing and/or distributor needed to be properly set up. Before taking everything apart it is definitely worth double checking. I had this problem with my GTO.

I am guessing that when you apply a little pressure to the throttle linkage you can get the idle down where it should be.

Best of luck,


Bill

[David L.]

Re: 1970 Rochester Carburator

All------


Also, while we know these things were used on 1970 Corvette Q-Jets, I can't find that they were ever cataloged in the Corvette P&A catalogs for any application.

Joe,

! agree. My 1970, 1972, and 1981 Chevrolet (exc. Corvette) Parts Catalogs ( Jan. 1970, Oct. 1970, Jan. 1972, and April 1981) list the following in Gr. 3.440:

70 Nova, Chevelle, Camaro w/Roch. 4BC........7038765.....DASHPOT ASSY., slow idle.

My 1972 (Sept. 1971), 1979 (June 1979), and 1982 (Nov. 1981) Corvette Parts Catalogs do not list GM # 7038765 in Gr. 3.440.

Dave