checking for intake leaks
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
checking for intake leaks
Have an air leak allowing the car to run 1000RPM idle with the butterflies completely closed. Checking for air leaks use soap test by where the runners end at the heads? Any flame test etc. ideas?
See my remarks on http://forums.corvetteforum.com/show...post1548523609
See my remarks on http://forums.corvetteforum.com/show...post1548523609
Last edited by Cali,68,L-79; Oct 13, 2004 at 09:06 PM.
Melting Slicks
Joined: Jul 2001
Posts: 2,609
Likes: 12
From: Massapequa Park NY
I use propane to check for @ find vacuum leaks. You need a straight valve though, not the usual torch since that mixes with air. With a rubber hose attached you can direct the propane where you wantto check. Since propane is heavier than air it doesnt get sucked into the carb unless you get close.
When you find the leak the RPMs will noticably increase. I also use it to double check mixture settings.
Jim
When you find the leak the RPMs will noticably increase. I also use it to double check mixture settings.
Jim
Burning Brakes
Joined: Feb 2004
Posts: 958
Likes: 1
From: In the Beautiful Shenandoah Valley of VA
Originally Posted by Cali,68,L-79
I heard that to. I'll try that or just gas and see if it seeps into the intake with the car running. Thanks.
David
David
Please don't use gasoline, you're asking for trouble with fire in the event of a spark or excess heat. Use carb cleaner or ideally propane and a variable valve like Jim described. Gasoline fires are something our Vettes don't need!
Steve
Melting Slicks
Joined: Jan 2004
Posts: 2,672
Likes: 1
From: New Cumberland PA
Originally Posted by lostpatrolman
I heard of spraying starting fluid around the carb base and other areas. The rpm will change when you do hit the area that is leaking.
I had a leak that I could hear and I knew the general area it was coming from but I could not say for sure where it was. I then got out the can of starting fluid and after a couple of quick shots at where I thought the leak was, the msytery was solved. The engine will noticable pick up in rpms, or at least it did in my case.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Originally Posted by 1970-Bronze
Ok, silly question but are we sure it's a leak and not the Carb? 
You may have to put the Edlebrock back on to verify...i'm sure that's not exactly what you wanted to hear.
You may have to put the Edlebrock back on to verify...i'm sure that's not exactly what you wanted to hear.
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Originally Posted by 70BBvert
I use propane to check for @ find vacuum leaks. You need a straight valve though, not the usual torch since that mixes with air. With a rubber hose attached you can direct the propane where you wantto check. Since propane is heavier than air it doesnt get sucked into the carb unless you get close.
When you find the leak the RPMs will noticably increase. I also use it to double check mixture settings.
Jim
When you find the leak the RPMs will noticably increase. I also use it to double check mixture settings.
Jim
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,938
Likes: 1
From: San Diego CA
Originally Posted by SLine78
David,
If your new manifold is a standard Performer, not the EPS, you should check at the rear of the carb where it mounts to the mainfold for your vacuum leak.
Mike
If your new manifold is a standard Performer, not the EPS, you should check at the rear of the carb where it mounts to the mainfold for your vacuum leak.
Mike
Melting Slicks
Joined: Jul 2001
Posts: 2,609
Likes: 12
From: Massapequa Park NY
Originally Posted by Cali,68,L-79
Silly question but do you use just propane (i.e. my propane braze kit) with the propane lite up with flame or just propane???
Just propane - no flames
You want the propane to be drawn in through the leak, it will then burn in the combustion chamber and cause a rise in RPM. A torch tip won't work though, you need a straight valve - like the valve on the propane (or map gas) & oxygen welding kits. Check out the valve on the map gas tank below. Attach a long rubber hose to the valve to direct the propane where you want to test & keep the tank verticle.http://www.bernzomatic.com/bernzomat...X2550KC_lg.jpg
Jim
Racer
Joined: Apr 2001
Posts: 395
Likes: 0
From: Shoreline WA
The standard performer manifold designed for spread-bore carbs, has a slight "V" at the rear of the carb mounting surface. When a square-bore carb is used without an adapter plate on this manifold, a tiny amount of the manifold carb inlet is left exposed, causing a hidden vacuum leak.
This is why Edelbrock states their square bore adapter plate #2732 is required for all Performer Series Carburetors (which are square-bore) when used on Performer manifolds for GM engines.
Mike
This is why Edelbrock states their square bore adapter plate #2732 is required for all Performer Series Carburetors (which are square-bore) when used on Performer manifolds for GM engines.
Mike
Melting Slicks
Joined: May 2002
Posts: 2,431
Likes: 52
From: Florida
I know this sounds odd but using a length of rubber tubing and putting one end to your ear and guiding the other end around your intake in close proximity to the engine will work similar to a doctors stethoscope. I've used this method for locating vacuum leaks and exhaust leaks. Use something larger than a vacuum line but smaller than 1" dia. for best results.
Jim
Jim
Racer
Joined: Jul 2004
Posts: 492
Likes: 0
From: Burlington Ky
I use starting fluid all the time at work to find intake leaks. It is the safest way. Use one that has a lubrcant in it. I don't know what propane would do to the pistons or valves, but NEVER use gasoline, one backfire and poof, there goes your harness. I had that happen on a fuel truck that had run out of gas. Poured some gas down the carb, some spilled, it backfired. It could have gotten ugly. I had a friend loose his prized '67 Mustang the same way. Also, I use a vacuum gauge in conjunction. You can tell a lot from it if you know what to look for. If it is twitching, you have a leak on one cylinder, ect.
Be safe
Be safe
Le Mans Master
Joined: Sep 2001
Posts: 7,739
Likes: 630
From: Unreconstructed, South Carolina
propane; yes
Originally Posted by 70BBvert
I use propane to check for @ find vacuum leaks. You need a straight valve though, not the usual torch since that mixes with air. With a rubber hose attached you can direct the propane where you wantto check. Since propane is heavier than air it doesnt get sucked into the carb unless you get close.
When you find the leak the RPMs will noticably increase. I also use it to double check mixture settings.
Jim
When you find the leak the RPMs will noticably increase. I also use it to double check mixture settings.
Jim
I run a late model stock at local circle tracks ... some are nascar sanctioned. One of our best local nascar-certified tech inspectors uses the propane method to check for air leaks around carb/restrictor plate. Our carbs/plates are restricted to limit max air flow. Such leaks matched to rich fuel jetting are purposely induced by cheaters ... such an air leak with appropriate fuel jetting will effectively increase air flow. Inspectors can & do toss leaking carb/plate and results when detected.