I'm trying to identify the original style choke pull-off for a '70 W31 Q-Jet, 7040255. Any one what an original should look like? I've seen units that are entirely white plastic and units that are all metal. I also have an original '70 Chevelle Q-Jet and the pull-off is half plastic (white) and half metal (but unfortunately broken).

Thanks.

 

The original 68-9 units I have seen are gray and black plastic.

Choke changed in '70 though...

so, I don;t know I guess. Can find a part number, from which maybe you can find one for sale or a photo of it?

 

Thanks for that info. I have a part number but I haven't come up with any images.

 

What is the part number? I have an NOS one but not sure what it is correct for.

 

your vacuum break(pull-off) should be all metal. i should have the part number stamped into it(at least 5 digits). the bracket that holds it is considered a separate part, and has it's own part number stamped into it. since the brackets were all the same on Olds 4m carbs. during that era, that number won't do you any good. those vacuum breaks are quite hard to find, as nobody is making them now. the correct part number is 7040697 for the break unit only, the bracket and break assembly is 7026162.


bill

 

According to my parts book, the one for my application is indeed 7040697. I bought a couple of plastic aftermarket pull-offs, I guess that was a waste. Thanks Bill for the insight, I know what to look for now.

Brian

 

This certainly answers my questions. I should have thought to ask you guys initially. I'm a bit pessimistic about find the correct one-oh well.

Thanks!

 

Metal can for "exc. High Perf." apps

http://www.ebay.com/itm/CHOKE-PULL-O...449a69&vxp=mtr



Plastic replacement

http://www.ebay.com/itm/NORS-Choke-P...42c2e6&vxp=mtr

Here's the gray & black plastic unit I have seen on factory performance carbs of he 67 68 69 era

http://www.ebay.com/itm/VTG-NOS-DELC...c900d5&vxp=mtr

Save the above photos for your records.
Set up an epay search to alert you when things like this appear.

 

What is the difference of the pull-offs between the ones for OAI on non-OAI?

 

The difference in all pulloffs to my knowledge is the size of the pinhole in the vac line tube. That orifice varies in size between various pulloffs and affects the rate of opening. Some serious tuners in the old days would drill them out and experiment with them. The length of the arm can vary between pulloffs, some have a hole and some an oval slot. Depends if it's a 4 BBL or 2 BBL and the make/model of carb. But...mostly it's that orifice diam, a 4BBL hi per and a 4BBL stock would have a different size and number, but look identical. When you buy a new pulloff now, they have like a universal orifice size to fit many aps, they might fit 15-20 GM aps that originally had different size orifices.

 

Thanks mrolds69 for the insight. It would be instructive to see the standard and high performance variants together and make some measurements.

 

With lower vacuum of the W31 and W30, would one expect the orifice hole to be smaller? Do you have a 7040697 that can be measured, perhaps by inserting a drill bit?

 

Thanks Joe for sharing that insight. I'm going to speculate with a lower engine vacuum available the orifice might be larger and the spring tension lower--just a guess. Alternatively if the objective is to have the choke closed longer on the hi-perf engines than I guess the orifice may be smaller.

My car has a plastic pull-off currently. I'm not aware if the after market ever offered a metal one calibrated for the 70 OAI application.

 

Pretty much nobody is any fussier than I, and I wouldn't lose any sleep over not having the exact # dashpot. Joe is probably right, the sping is most likely different also. A replacement will do the job for you, nobody starts their W-car in Michigan when it's 25 below zero anymore. Finally, it's not a part you would be docked any points for at the OCA Nats or any judged show.

 

dashpot?

we're talking vacuum breaks.


bill