| 403 Quadrajet vacuum leak [message #256035] |
Mon, 21 July 2014 16:28  |
Francois
Messages: 161
Registered: October 2012
Location: Southern California
Karma: 0
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I've had some serious engine trouble in the last few months. The 403 in my 78 Royale started running really slowly and bad on a relatively short trip.
I found part of the problem in a broken hydraulic lifter. I replaced them all.
In the course of doing the project I also rebuilt the Quadrajet 4 barrel carb - per a helpful Youtube series. Now it's all back together and my dash vacuum gauge shows basically zero vacuum. I know this must be because I am connecting it all up wrong, but it all looks right.
I am in need of a process by which I can systematically diagnose a vacuum leak, and a diagram showing which tubes go where.
Does anyone have any suggestions where I might search for this information? I would appreciate it. It's my last attempt to fix this problem myself. If it fails, I will bring it in to someone who does this mechanic stuff for a living.
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| Re: 403 Quadrajet vacuum leak [message #256183 is a reply to message #256035] |
Tue, 22 July 2014 23:48  |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Senior Member |
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Where is your vac gauge connected?
I could be wrong, but I dont know of a factory option so it wouldnt be in the schematic
You want it to go to manifold vaccuum. It can T in anywhere you have a constant source
What type of tubing does it use?
If you have it to the ported vac port on the qjet it wont have vac at idle.
Have you verified the gauge and line with a Mity-vac or similar tool?
76 Glenbrook
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| Re: 403 Quadrajet vacuum leak [message #256196 is a reply to message #256035] |
Wed, 23 July 2014 05:59 |
Steve
Messages: 506
Registered: September 2013
Location: East Greenville, Pa
Karma: 1
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Senior Member |
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It sounds like you may be connected to a ported vacuumed source on the Q jet. There should be two on the Q jet, one ported and one non ported that is straight manifold vacuum.
I used to chase down vacuumed leaks with carb cleaner. If you spray it near a leak it will cause an engine rpm surge. That was the old days, not sure if there is a safer method or spray to use.
1978 GMC Royal
Eastern Pennslyvania
1968 Chevrolet C20 396 Camper Special
1969 Chevrolet C20 Camper Special
1985 Buick Electra Park Avenue
1992 Camaro 25th Anniversary Heretage Edition Black
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