Vacuum leaks - Pontiac GTO Forum

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post #1 of 9 (permalink) Old 12-03-2012, 10:56 PM Thread Starter
 
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Vacuum leaks

EUREKA!!!! Finally found the blasted vacuum leak that had been plaguing my veritable sanity! The PO concocted this crazy brass block setup at the rear of the carburetor, which I attempted to just go ahead and replace with all new pieces, just match them and replace. NOT so easy. After going to 5 different auto parts stores, Lowes, and 2 alternate hardware places, no one could even come close to what was there. ( 2 of the auto parts stores told me that most of their brass fittings were being removed, as smokers of illicit drugs were using them to make smoking apparatuses!- One place even had the audacity to try to ID me when I purchased a fitting! I told them to cram it, and give me the part-which they did!). ANYway, after 15 solid months of spending 8-18 hours a day out in the garage, it actually feels like I'm making progress. (I might have had 30 days off total in that time) One of the brass blocks had a hairline fracture in it- NOT really noticeable, looked like a casting mark. Spraying it with carb cleaner made no rpm change at all. Pulled all that garbage off the back, installed a threaded barb, connected the booster line to that and cranked it up- WHAT A DIFFERENCE! It now idles smooth in gear!!!! Now BOTH idle mixture screws actually function! All I have to do now is connect the vacuum modulator line up. (NOT to the rear again- hopefully it will function properly connected to the front port on the drivers' side of carburetor. I also moved the advance line to the right side timed port-she likes that spot!). I had to take a few steps back and a few deep breaths and start fresh. THANKS TO ALL who helped me through this grueling process. My confidence level has finally risen, at least to the surface! THANKS!!!!
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post #2 of 9 (permalink) Old 12-04-2012, 01:04 AM
 
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:beer: cheers!
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post #3 of 9 (permalink) Old 12-04-2012, 04:40 AM Thread Starter
 
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vacuum leaks

Just came in from garage a few minutes ago (4:33 a.m.). Have already had an celebratory beer or two, as it were. Today, I will purchase vacuum lines and the like, then drive that puppy around and see what she'll do for me. It should be an momentous occasion.
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post #4 of 9 (permalink) Old 12-04-2012, 07:15 AM
 
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Congrats!

1968 Pontiac GTO
1983 Pontiac Bonneville (G) wagon
2008 Pontiac G8 base
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post #5 of 9 (permalink) Old 12-04-2012, 02:03 PM
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If you have a Quadrajet, the modulator line connects to the 1/4" fitting on the passenger side of the carb, at the front. The vacuum advance connects at the driver's side, and is manifold vacuum, not ported. Great that you got it running much better!!
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post #6 of 9 (permalink) Old 12-04-2012, 04:30 PM Thread Starter
 
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vacuum leaks

Nope, GTO guy, there's a Carter competition carb on it. I've read a few posts about that, and they all said the pass. side was the timed side, and the left side was full vacuum. If that is not the case, then the parts I bought today won't work because I know that the trans. needs manifold vacuum, and I'll have to find another spot to stick the modulator line. There seems like some force is resisting tooth and nail over every little item I try to fix on this beast. I'll know soon enough, though- heading back to the garage right now- we shall see.
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post #7 of 9 (permalink) Old 12-05-2012, 12:55 AM Thread Starter
 
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Carter carb.

ok after reading about 100 posts, the vacuum port configuration on the front of this Carter 9635 is still elusive. Seems 50 posts say the timed side is the RIGHT SIDE, and 50 say the LEFT side is the timed side. I suspect that 50 believe the actual LEFT DRIVERS' side is not the left to them, because they're looking at it from the front of the engine. Looked at Edelbrock site- they show a picture, and nothing else. Not a word. IS THE LEFT SIDE (DRIVERS' SIDE) MANIFOLD VACUUM, OR PORTED ON A CARTER COMPETITION SERIES 9635SA?????????????
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post #8 of 9 (permalink) Old 12-05-2012, 09:17 AM
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Here's how to make it simple: There are two types of engine vacuum: manifold and ported. Manifold is below the throttle plates and ported is above the throtle plates. The transmission modulator must be connected to manifold vacuum for it to work. As the throttle is opened, manifold vacuum drops, but the velocity thru the carb causes the ported (above throttle plates) vacuum to increase. Like a see-saw. Easy to check. Pull a hose and if it's sucking air at idle (like a PCV line or a vacuum advance line) it's maniflold. If you have to rev the engine to get suction on the line, it's ported.
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post #9 of 9 (permalink) Old 12-05-2012, 12:11 PM Thread Starter
 
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vacuum leaks

Thanks geeteeohguy. That's the answer I was looking for. I knew it was that easy- sometimes I can't see the forest, for the trees. I try to look for the most complicated of answers it seems, when the "real" problem is right under my nose!
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