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Unread 06-04-2008, 08:51 PM   #1
PaulS
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1949 CJ3A 
 
Join Date: Jun 2008
Location: Edmonton, AB
Posts: 83
Effect of vacuum leak

The previous owner of my 1950 CJ3A installed a vacuum gauge. The problem is that the hose to it leaks--to the point where you can hear the leak when the engine is running. The leak is obviously very close to the gauge, and not in the engine compartment.

I'm just curious what the effect of that leak would be on the engine performance. Any comments?

Off the top of my head I don't know where the vacuum line is connected (if it matters), but I will certainly find out. As soon as my little boy is asleep, I'll probably head out to start pulling steering components (see other threads...) and I'll check that line while I'm out there. I'm not ready to start dealing with engine performance yet--brakes and steering come first--but I can't stop thinking about lots of different things that will need work over the next while...

Thanks,

-Paul

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Unread 06-05-2008, 06:46 AM   #2
PaulS
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1949 CJ3A 
 
Join Date: Jun 2008
Location: Edmonton, AB
Posts: 83
Checked, and the vacuum line ports directly into the intake manifold--specifically, the flow passage to the #4 cylinder. What would be the effect of a vacuum leak there?

-Paul
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Unread 06-05-2008, 09:31 AM   #3
Mike Romain
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1986 CJ7 
 
Join Date: Nov 2007
Location: Off the Grid in Chester Grant, Nova Scotia, Canada
Posts: 12,554
Quote:
Originally Posted by PaulS View Post
Checked, and the vacuum line ports directly into the intake manifold--specifically, the flow passage to the #4 cylinder. What would be the effect of a vacuum leak there?

-Paul
Normally the engine runs lean on all cylinders because of lack of vacuum which ups the RPM and can burn a hole in the leanest piston, #4, if you let it go on too long.

The only tricky part is if the last owner set the carb mix and idle speed up 'with' the leak present. The setting will be off after you fix it if this is the case, so if the idle drops too low you have an idea of what to go for.
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86/00 CJ7 Laredo, 33x9.5 BFG AT's, 'glass nose to tail in '00, 'New' frame,wires and plumbing in '09. Carter BBD Carbed 4.0 HO in '10.
89 YJ Renegade. BBD Carbed 4.0 HO. Locked front and rear with 33x9.5 BFG AT's
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Unread 06-05-2008, 09:56 AM   #4
PaulS
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1949 CJ3A 
 
Join Date: Jun 2008
Location: Edmonton, AB
Posts: 83
Thanks! The carb needs adjustments now anyway, so I'll deal with the leak before doing it. (I also need to put some good gas in the tank before doing the adjustments--the stuff there now is months old, and I'm sure that doesn't help the engine run well!)

-Paul
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