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Unread 05-29-2007, 06:22 AM   #1
motojoe
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Vacuum leak?

Could a weak power booster(brakes) cause a vacuum leak? My idle is low due to a vacuum leak. I can close the choke plate to almost closed and it idles fine. That to me indicates a lean running condition. There for I think I have a vacuum leak.
My brakes have been weak and require more foot pressure to apply them. I want to swap out the BBD carb for a MC2100, which I have already. But before I do I want to solve the vacuum problem. I have sprayed around every place I could with choke/carb cleaner to see where the leak is coming from(vacuum hoses, manifold, carb base etc...). All the vacuum hoses are in good condition. Any suggestions?

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Unread 05-29-2007, 06:50 AM   #2
79cj7reny
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To test the booster, pump the brake pedal a few times with the engine off. hold the pedal down with light leg pressure. Then start the engine. when the engine starts, you should feel the pedal drop a little and the pedal effort should decrease. If not, your booster is shot.
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Unread 05-29-2007, 07:23 PM   #3
motojoe
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Booster= shot. Still does not explane vacuum leak. Thanks for trying...next?
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Unread 05-29-2007, 07:40 PM   #4
slacker92104
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If the diaphram in the booster has a hole in it, that would explain the weak brakes, and the vacuum leak.
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Unread 05-29-2007, 07:42 PM   #5
mikepatrick
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If the booster is shot and you have a vacuum leak then the vacuum diaphram in the booster is leaking. Pull the hose off of the booster and plug it. I bet your vacuum leak goes away.


Slacker beat me to it.
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Unread 05-29-2007, 07:55 PM   #6
John Brereton
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A friend of mine had a bad diaphram in the booster that some how sucked the brake fluid out of the resevoir and into the intake. The exhaust smoked like an SOB.
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Unread 05-31-2007, 03:26 PM   #7
motojoe
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Problem solved. Installed an MC2100 and that took care of the vacuum leak.
Idles better now. I do need to replace the booster though. Brakes are weak and it takes allot of foot pressure to apply them. Thanks for the help.
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Unread 05-31-2007, 04:52 PM   #8
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If you have to replace it anyway, you might look into the yj booster swap.
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Unread 06-01-2007, 11:01 AM   #9
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Quote:
Originally Posted by motojoe
I do need to replace the booster though. Brakes are weak and it takes allot of foot pressure to apply them. Thanks for the help.
Have you verified the HG level at the booster? You need a minimum of 16 HG and a prefered level of 22HG inorder to activate the booster correctly. many engines with RV cams or just tired motors struggle to reach that level of HG. If that is the case with your rig, you will always have booster issues.

There are vacuum assist pumps that will solve this very easily such as the one by Stainless Steel Brakes :

http://www.jegs.com/webapp/wcs/store...5962_-1_764262
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Unread 06-01-2007, 11:23 AM   #10
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Let us know how you like the MC conversion!! I just did mine a couple weeks ago, and I like it so much I am gonna hold off on fuel injection!!!!!
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Unread 06-01-2007, 08:30 PM   #11
motojoe
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Quote:
Originally Posted by 79cj7reny
To test the booster, pump the brake pedal a few times with the engine off. hold the pedal down with light leg pressure. Then start the engine. when the engine starts, you should feel the pedal drop a little and the pedal effort should decrease. If not, your booster is shot.
Got a new booster. The old one was toast. Old brake fluid seeped in over the years causing it to go bad.
Yes, I love the MC2100 on it. It starts up easy and runs great. No issues. I recommend the swap to anyone who wants a better carb than the stock Carter BBD.
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