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Discussion Starter #1
First, as I don't trust anything on my car to be original, I checked my carb casting numbers 7041213 DM 1661, they do seem correct for my car.

Now my 2 questions.

#1 - I recently went out and bought what I thought was the correct carb to brake booster line but the nut on the new hard line is too big for the opening on the carb plate. So either I ordered the wrong part, power brake vacuum booster pipe, or the car I bought had the carb plate changed. Do I just go and buy a nut to adapt the small hole to the large pipe? I'd like it to fix it correctly without an adapater nut.



#2 - I think my spring for the throttle return looks a bit funny and kind of Bubba-ish but I'm not sure. I think the spring should be located differently but I can't find a good picture of what mine should look like. Is it incorrect?




I'll be getting my exhaust in on Monday, so hoping for a startup next weekend. :thumbsup:

Thanks,
Jeff
 

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I'm not 100% sure on #1 since I don't have power brakes and have never messed with it, but you might check to make sure the hole in the carb plate is meant to be used with an inverted flare. Looks like the old fitting has pipe thread. Maybe there's supposed to be a male pipe thread to female inverted flare adapter in between them? :huh:

As for #2, my '69 has that same thermostat housing with the little tab and hole in it for the spring. Standard operating procedure would be to have two throttle return springs so that if one fails you still have the backup to make sure the engine doesn't rev out of its mind. So I'd say leave your current spring (or replace it if you don't like orange) and add one in the location you have noted :thumbsup:

Looks like your primary throttle shaft bore is leaking as well based on the discoloration of the intake manifold just below it. That's a common problem on the Qjet and can be risky business as it allows fuel to pool on the hot intake. I used Cliff Ruggles' bushing kit to fix mine. He also has a great book on how to rebuild and modify these suckers. I think I found mine on the shelf at Barnes & Nobles.

Good luck on the first startup! :excited:
 

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You have the correct pipe but you're missing the adapter, NPT to inverted flare

The double spring goes where you drew the circles.

You may or may not have a gas leak, but the discoloration is common from the exhaust crossover.
Make sure the flapper on the pass side exhaust is open and operates freely.

 

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Discussion Starter #4
You have the correct pipe but you're missing the adapter, NPT to inverted flare

The double spring goes where you drew the circles.

You may or may not have a gas leak, but the discoloration is common from the exhaust crossover.
Make sure the flapper on the pass side exhaust is open and operates freely.
So an adapter is stock procedure then. Certainly the "thing" that's on there now is not stock with the rubber hose with hose clamps around it. The rubber the previous owner put on went to a hard pipe that had connections for both the brake booster as well as the main vacuum line. I couldn't find that specific pipe on any Corvette parts site I looked at. It's almost certain it's from a non-Corvette car.

Are you sure a 1971 base 350ci/270hp with the Rochester had a dual spring? I've looked at all of the big sites like Ecklers, Paragon, Zip, etc and all seem to have a single spring like this one:



and this:




As for a leak, there may be, I've probably had the engine running a total of 10 minutes before I tore into things and I'm not ready yet to fire it up. Either it's a leak from the carb or there was some oil leaking from the valve seals. This whole engine stuff is new to me, so knowing that Q-Jets are known to leak at the throttle shaft is important. Would it leak the same way on both sides of the carb as both sides of the carb in the middle above the valve covers are dark colored like that. I did look at the bushing kit and once I get it running again, if it's leaking I'll be sure to do the mod.

If you meant heat riser valve by saying "flapper on the pass side exhaust is open", I have my exhaust off right now and it looks like the previous owner basically made it into a spacer:



Thanks for the info!
 

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You can also find a Chrome GM Dual Spring Set at AutoZone and add a bit 'o bling for a few bucks.

pretty sure most GM vehicles w/Q-Jets had dual springs. My 69 Firebird 400 had both, as does my 78.
 

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Discussion Starter #8
It seems they came both ways. My water outlet has the tab for a spring connection. So there's one going from carb to water outlet. And there should probably be one in the picture where I drew the line as a backup. So in my case, the single one from Ecklers would probably be the correct solution.

However I'm replacing my thermostat and was thinking of going chrome for the outlet and it won't have a tab, so I'll be going with the double spring where I indicated a missing one.

I think the important note on this is that you should have 2 springs, either separate or one inside the other.



 

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Everyone is correct about the NPT to inverted flare adapter and the dual springs.
But a note of caution about both-

The NPT is short for "National Pipe Taper". As in tapered threads- tighten it too much and it's possible to crack the carb base. (points off)

The second is the carb return springs. Use just enough spring to return the carb to idle. Too much tension on the spring and it'll wear the throttle shaft bore, causing a vacuum leak. Won't happen right away, but it's still a point to watch for. The dual spring thing was installed by GM on just about everything. The thinking was that if one spring broke the other would still be there. And that's saying nothing about the leg muscle you'll get from using a too stout spring.:thud:
 

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Discussion Starter #10
Everyone is correct about the NPT to inverted flare adapter and the dual springs.
But a note of caution about both-

The NPT is short for "National Pipe Taper". As in tapered threads- tighten it too much and it's possible to crack the carb base. (points off)

The second is the carb return springs. Use just enough spring to return the carb to idle. Too much tension on the spring and it'll wear the throttle shaft bore, causing a vacuum leak. Won't happen right away, but it's still a point to watch for. The dual spring thing was installed by GM on just about everything. The thinking was that if one spring broke the other would still be there. And that's saying nothing about the leg muscle you'll get from using a too stout spring.:thud:
I went yesterday to my Corvette warehouse place where they carry old C3 parts and found a Rochester carb with my NPT to inverted flare nut, so I'm golden there! :thumbsup:

I tried the double spring from Advanced Auto but it's 4" long and I measured the space between the 2 connectors and it's only 3-1/2" long:

So that part is going back and I'm going to try the short, black spring from Paragon that I had posted previously. I'll just leave the one from the water outlet to the carb alone and will be my backup.

I'm also having trouble finding a *reasonably* priced 14" air cleaner to fit my Rochester carb. I bought one for $40 from Corvette Specialties an hour away from me thinking they'd know exactly what I need. Turns out my choke linkage is too high up for the inner flange so I'd need a spacer to lift the cleaner up. I'm not ready to throw some cheap spacer on there if I can find a correct 14" base that will work. I then bought another 14" one from Advance Auto that they had in stock (Mr Gasket) that was perfect fit on the carb base but it doesn't drop the air cleaner down enough for the hood. The reason I'm changing out my dual snorkel out? I just ordered my HEI distributor and need some extra room around the cap.

Any suggestions on a 14" air cleaner that will clear the carb top without spacers and still keep the filter low enough for clearance?
 
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