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Author Topic: 7040202 APT  (Read 2011 times)

Offline mcx

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7040202 APT
« on: January 26, 2019, 04:23:18 AM »
Hello Cliff...I picked up another cheap QJET from ebay this time...its a 7040202 and supposed to from 1970 350 auto Chevelle/Camaro/Corvette...it's a bit crusty but came apart easy enough and it seems all there...it's different from other two(Buick/Caddy) in the  air horn bleeds are not the small "bushed" type... and that the APT is set so low it's flush with the base plate, it's not even up to the gasket?  Is this how it came from the factory, it would seem the primary rods would never get out of the jet?...anyway, it's soaking in Wd40 as it is buried in carbon.   Thx, Mike
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Offline Cliff Ruggles

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Re: 7040202 APT
« Reply #1 on: January 27, 2019, 02:53:21 AM »
1970 was the first year for the large MAB's on the Chevy units.  They stuck with that for a few years then went to SMAB on the divorced carbs in 1977 an 1978 (truck carbs).  The larger MAB's were finally phased out by 1980 and the SMAB was used till the end of production on the non-CCC units......Cliff
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Offline mcx

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Re: 7040202 APT
« Reply #2 on: January 27, 2019, 05:51:52 AM »
Thanks Cliff...I know the factory  APT settings are differant from application to application, but is it common to see no primary hanger lift ,as this one?  The primary rod piston bottoms out? Thx,Mike
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Offline Cliff Ruggles

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Re: 7040202 APT
« Reply #3 on: January 28, 2019, 04:24:46 AM »
Yes, I've seen them from no lift at all to up pretty high on the same part number.

Those units were factory tuned and why we like to remove the stock APT screw and use our adjustable one with a spring on it to hold it's adjustment.

They can be a PITA to get out of some baseplates, but well worth the effort.......Cliff
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Offline mcx

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Re: 7040202 APT
« Reply #4 on: February 02, 2019, 07:05:19 AM »
Cliff...this 7040202 has no ported vacuum feature...you see any issue with me carefully drilling a passage in the main body and in the correct spot in the base plate? Thx,Mike
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Offline mcx

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Re: 7040202 APT
« Reply #5 on: February 02, 2019, 12:55:53 PM »
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Offline Cliff Ruggles

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Re: 7040202 APT
« Reply #6 on: February 02, 2019, 04:35:01 PM »
Yes, 1970 was a goofy year for carburetors as the factory used TCS to the vacuum advance instead of directly from the carburetor via ported vacuum.

When a Q-jet is set-up to apply the vacuum advance via ported vacuum it is "all in" right off idle as they used a very precisely located hole in the baseplate that is completely uncovered with very little throttle movement.

Even so you'll read all over the NET that your an idiot if you don't use MVA to the distributor with rumors of extra cooling to improved fuel economy to not pinging at heavy and WOT. 

ALL of that for the most part is just regurgitated and outdate information on the subject.  The real truth is that the ONLY difference between using MVA and ported (with a correctly located source) is that you have no vacuum advance idle and coasting, it is exactly the same in all other scenarios.......Cliff
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