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7/8/16 9:58am - Original Message: 'carb'
dwa175 Gold Member
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oakville, CT - USA

Vette(s):
1979 coupe and now 2007 c-6

Joined: 7/19/2014
Posts: 183
looking for help. this old man .79 l-48 stock engine and carb,at ilde  when I full throttle are the rear   throttle plates don't open    what I use,t remember I don't,any advise   dwa 175 

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7/22/16 3:48pm - Reply: 'Re: carb'
snake97
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Metairie, LA - USA

Vette(s):
1979 Black, Oyster interior purchased in March 1980

Joined: 7/7/2013
Posts: 24

I 'm having trouble understanding your question. I have a 79 with a quadrajet and I'm guessing that is what you are talking about. The secondaries are controlled by vacuum. At idle and then raising rpm's to check if secondaries are opening may not be an accurate way to tell if secondaries are opening. I have a q-jet that was built by Sean Murphy, and when you are driving and give it full throttle, when the big secondaries open up you know it. You can feel and hear it. Even on a stock L-48 like I had, you know. If your secondaries aren't opening up, I suggest a carb rebuild and make sure you have no vacuum leaks. I've rebuilt stock q-jets and they are easy to rebuild. I wanted a tricked out q-jet so that is why I bought a SMI q-jet. Once again, check vacuum as there can be plenty of places for a leak on a corvette and then rebuild carb if needed.


Sorry if I led you to believe there is a vacuum secondary linkage like holley carbs. The quadrajet vacuum for the secondaries comes from the venturies on the primaries. The choke does have to be wide open and the engine will have to be at higher rpm for the secondaries. The quadrajet is a bit more technical than a holley , but on a street engine, a good quadrajet is great. It takes a bit more time and effort to adjust, but when you have it adjusted properly, it flat out works. The small primaries give it super throttle response and like I said earlier, when the secondaries open up when your engine is at the higher rpm range, it almost feels like you gave it a shot of nitrous. I've been playing with caes since the mid 70's street racing and drag racing at the local strips and the first thing I would always do was ditch the quadrajunk and get a holley. I even did that when I bought my Corvette in 1980. Afew years later I decided to go back to the quadrajet because I wanted the original back on. Once you learn about how they operate and fix the few things that were problems[fuel drippage from the plugs on the bottom], you will find out they are a good carb



|UPDATED|7/22/2016 1:48:22 PM (AZT)|/UPDATED|
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7/8/16 12:33pm - Reply: 'Re: carb'
dwa175 Gold Member
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oakville, CT - USA

Vette(s):
1979 coupe and now 2007 c-6

Joined: 7/19/2014
Posts: 183
yes  1979 cor  350 ci    yes quad  they do not open,idle is perfit,starts and runs normal,pulled off vaccum hose,it very  I did not have vaccum test at this time,i think what I am asking  is there something wrong with quad   car runs pefect  with only 2-barrel I did not pull off hole air cleaner off just top of air cleaner,seems that  they stuck,but no they are,i just needed I what I sould be looking,vaccum leak?  or something that's goes bad with quad 4,s   thanks for your reply.dwa

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7/8/16 9:39pm - Reply: 'Re: carb'
Adams' Apple Lifetime Member
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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
Posts: 19458
Quadrajets use a mechanical secondary. They will NOT open if the choke is closed, even a little. There is a small lock-out tab that will keep the secondary shaft from twisting the blades open if the choke is on. Once the choke is fully open, the tab drops, and then the secondary linkage will open the plates. Check your choke first. Then  maybe spray a little WD40(or similar lubricant) onto the choke linkage/lock-out on the passenger side of the carb....the tab may just be stuck. Make sure the vacuum pull-off valve is pulling the linkage when the car starts, too.  Thumbs Up











|UPDATED|7/8/2016 7:39:57 PM (AZT)|/UPDATED|


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7/9/16 9:33am - Reply: 'Re: carb'
dwa175 Gold Member
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oakville, CT - USA

Vette(s):
1979 coupe and now 2007 c-6

Joined: 7/19/2014
Posts: 183
thanks  for your  input   that's want I been looking for,if I was still turning wrechs it would no problem getting  problems  just old age. I will say there seems do no vaccum leaks  car runs fine  with a 2 barrel carb,next step is remove hole air cleaner and check carb,  I thought the rear plates were stuck   wd- 49   .will do,  I well tell problem can be fixed  by cleaning.good luck you say.dwa

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7/16/16 11:08am - Reply: 'Re: carb'
dwa175 Gold Member
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oakville, CT - USA

Vette(s):
1979 coupe and now 2007 c-6

Joined: 7/19/2014
Posts: 183
yes  found sec lever would not open lock out on carb holding it closed,all  works fine,i pushed lever fro choke open all works fine,dont now what adjustment there is or maybe just stuck,it works fine now   let it cool down and try again   .    there must be something that holds back  seems everything is to loose but your pic pointed right to it    good job thanks dwa

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