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Vaccum leak on 73

bmack

Member
Joined
Dec 14, 2005
Messages
21
Location
windsor
Corvette
73 blue coupe
Could someone please help me on a easy way to find and troubleshoot a vaccum leak. The engine won't idle below 1000rpms and the engine seems to lope on that idle speed. Thank you.
 

fine69

Well-known member
Joined
Dec 12, 2004
Messages
975
Location
Maryland / D.C.
Corvette
'69 Convertible Vette; '72 Z28 Camaro Rally Sport
bmack said:
Could someone please help me on a easy way to find and troubleshoot a vaccum leak. The engine won't idle below 1000rpms and the engine seems to lope on that idle speed. Thank you.

This may sound elementary, but is your timing is correctly?

I had major problems with idling. I closely followed the articles, "Timing & Vacuum Advance 101" and "Mapping Your Advance Curve" written by JohnZ and got my timing set correctly. The performance is now the best it's been since I've owned it, and the engine idles at 750 rpms.

If you want, I can forward you a copy of these articles. They're excellent reference material and easy to follow. JohnZ is quite amazing with his detailed knowledge in G.M. engineering.
 

6880 Mike

Well-known member
Joined
Jun 30, 2006
Messages
2,723
Location
The Bluegrass State
Corvette
1968 convertible; 1980 L-82
The most common area for a Corvette vacuum leak is the headlight vacuum circuit. You can often hear the leak.
 

waterboy1976

Well-known member
Joined
Aug 18, 2003
Messages
510
Location
Cleveland,Ohio
Corvette
1973 4-speed Coupe FOR SALE/ SOLD!!!!
High idle may also be the carb running rich..and out of adjustment. I thought I had a vacumn leak but found out :D otherwise.....
 

Bob Onit

Member
Joined
Jul 15, 2006
Messages
7
Location
Ct
Corvette
Very Clean 73 Coupe,L48 New paint
Hi All .... First post here

Providing your car is stock.
Take a pair of forceps and start by pinching off the main vacuum at the rear of the intake manifold (just behind the carb) If the idle drops you have eliminated the carb as the source of the Vacuum leak..If the Idle doesnt drop then the leak is related to the carb...warn throttle shaft bushings, missing hose/ plug ect:
Using the forceps just continue your way in a linear mode pinching off one section at a time as hoses merge or split,
Sooner or later you will find the leak

I would also use a vacuum gauge to test the full vacuum off the Intake manifold (Same place as posted above)
Hopefully you will have somewhere around 18-20 "hg at 750 RPM (If you can get it that low)

It can take a while, It took me about an hour to find the manual headlight valve under the dash was leaking...

Keep at it and you willl find it.
Good luck
 

waterboy1976

Well-known member
Joined
Aug 18, 2003
Messages
510
Location
Cleveland,Ohio
Corvette
1973 4-speed Coupe FOR SALE/ SOLD!!!!
Bob Onit said:
Hi All .... First post here

Providing your car is stock.
Take a pair of forceps and start by pinching off the main vacuum at the rear of the intake manifold (just behind the carb) If the idle drops you have eliminated the carb as the source of the Vacuum leak..If the Idle doesnt drop then the leak is related to the carb...warn throttle shaft bushings, missing hose/ plug ect:
Using the forceps just continue your way in a linear mode pinching off one section at a time as hoses merge or split,
Sooner or later you will find the leak

I would also use a vacuum gauge to test the full vacuum off the Intake manifold (Same place as posted above)
Hopefully you will have somewhere around 18-20 "hg at 750 RPM (If you can get it that low)

It can take a while, It took me about an hour to find the manual headlight valve under the dash was leaking...

Keep at it and you willl find it.
Good luck

Not to hijack this thread but WELCOME Bob!!!! Nice C3 too...:upthumbs
 

Bob Onit

Member
Joined
Jul 15, 2006
Messages
7
Location
Ct
Corvette
Very Clean 73 Coupe,L48 New paint
waterboy1976 said:
Not to hijack this thread but WELCOME Bob!!!! Nice C3 too...:upthumbs
Thanks WaterBoy
I diddnt realize I posted pics of my car because I cant find them in my profile :L
 
T

tx73vette

Guest
Welcome Bob ... Hope that you can find the problem with your 73

Dan
 

Bob Onit

Member
Joined
Jul 15, 2006
Messages
7
Location
Ct
Corvette
Very Clean 73 Coupe,L48 New paint
Welcome Bob ... Hope that you can find the problem with your 73

Dan
I fixed my leaks TX
I was replying to bmack about his vacuum leaks :D


Could someone please help me on a easy way to find and troubleshoot a vaccum leak. The engine won't idle below 1000rpms and the engine seems to lope on that idle speed. Thank you.
 

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