carb vacum lines - Team Camaro Tech
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post #1 of 5 (permalink) Old Jan 31st, 01, 03:50 AM Thread Starter
Join Date: Jan 2001
Location: gloucester, virginia USA
Posts: 2

I bought a 80, when I got it home i noticed that the vacum lines to the distibuter were off. according to the diagram there is supposed to be two lines one from the front of the carb and one from the back. I don't have the vacum delay on it wasn't there. The Carb was rebuilt before i bought it. It's a quadrajet. is this going to affect the performance? Also The secondaries don't seem to be opening right. I checked the vacum lines for it, but it still doesn't seem to have much power. The engine is a stock 305. and the gas milage stinks. less than 12. I am giong to have the timing reset and the carb tuned this weekend... any advise, and should i consider going to a holley 4 instead of the quadrajet?? thanks in advance!

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post #2 of 5 (permalink) Old Jan 31st, 01, 06:55 AM
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Join Date: Mar 2000
Location: Dtown PA
Posts: 820

well the problem with the quadra-junk is that its a spreadbore carb, meaning the primaries are small, and the secondaries are about the size of a beer can,. or close to it,. you would need to go down to pep boys, or whatever parts store avail and get the edlebrock spreadbore adaptor, it allows just what you mentioned, because you still have a spreadbore manifold most likely.

as far as vacuum goes, test a port on the engine, see if theres any leaks, make sure that you have vacuume to the booster, and the canister, on the early 80's cars the cruise was controlled by vacuume. along with a few other accessories, now not every single port on the carb would necesarily utilize a hose, hence the little rubber caps on them. if in doubt, plug it.

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post #3 of 5 (permalink) Old Jan 31st, 01, 10:15 AM
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Join Date: Dec 2000
Location: Monroe, WA, USA
Posts: 312

the Q-jet is a fine carb!!!IMHO

there are lot's of thing's you can do to improve performance. as for the secondary's not opening, i bet the spring tension is off.

get a good book on the Q-jet and read it. or do a search on here for Q-jet stuff. but get the book!!

the Q-jet is a very good carb. it give's you outstanding economy and power! holly tried to copy it, it's root's are in the carter AFB line. in fact the carter AFB and Q-jet are the only tune and forget carb's out there. a holly and it's clone's allways need to be tweeked.

good luck and have fun!
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post #4 of 5 (permalink) Old Jan 31st, 01, 01:03 PM
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Location: skiatook, ok
Posts: 3,692

I would take a q-jet over a holley any day! Those small primary bores give great throttle response and fuel economy and when you nail it, those monster secondaries can make great power. The reason most people hate q-jets is because they are a pain to set up properly and the internals can be complicated to work with.
Why do you think your secondaries arent opening? Just looking in the top of the carb and whacking the throttle while in park means nothing...theres not enough load on the engine to cause the secondaries to kick in. This is why most people think that their carb isnt working right, but it isnt a valid test. What kind of mods (if any) have been done to the car? What kind of exhaust system? If you are running a stock exhaust system with catalytic convertor, take the car to a muffler shop and have them check the backpressur of the exhaust system to see if it is plugged up...convertors do go bad and when they do, the honeycomb in them tends to clog up and the engine cant breathe. As far as your vaccuum advance is concerned, there should be a sticker on the at the front of the engine compartment (normally around the top of the radiator area in plain site) that will have a diagram of the vaccuum hose routings.
Now this is a topic that everyone has their own opinion on...manifold vs. ported vaccum for the vaccuum advance. I believe gm used manifold vaccuum on nearly every 305 made...manifold vaccuum is highest at idle and drops with an increase in throttle opening. However, I have found that this tends to give an engine too much timing at low speeds and normal driving and can give them a low speed miss that wont go away with tuning. I almost always set up my engines with ported vaccuum for the will be 0" at idle and will increase as the throttle is opened up to a point, and then will go back to 0" at higher revs (this is without using wide open throttle)...this allows you to set your initial timing higher for beter low speed response without excessive low speed vaccuum advance. Either way you decide to go, you need the vaccuum advance...its only purpose is for fuel is inoperative at full throttle.

Sorry this is so long...hope it helps.

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post #5 of 5 (permalink) Old Feb 1st, 01, 04:22 AM Thread Starter
Join Date: Jan 2001
Location: gloucester, virginia USA
Posts: 2

Ok thanks for the info. I guess I didn't exactly say what I was thinking. according to the diagram there are two vacum lines that run to the vacum advance. one of them is supposed to have a 20 second delay on them for when the car is first started. This is the one on the back. then both lines come into a tee and go to the vacum advance. the question is will only having one affect the time on the car? And the question that Travis had about the exhaust system. the previous owner. had a single exhaust muffler put on it. I don't know what type... I want to put a true dual exhaust system on it but it looks like I will have to have one fabricated since I haven't been able to find one. I thought the 79s and earlier had that...(True duals) Could the single pipe out the back be causing the back pressure as well? And I'm not sure of the laws in virginia. but i wonder if i can remove all the smog equipment off the car, I know this will add a couple of horses. Any help will be appreciated. Thanks.
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