Late C3 Era Question
Thread Starter
Drifting
Joined: Jun 2009
Posts: 1,287
Likes: 448
From: Upstate NY
Late C3 Era Question
Ok, I have a C7 corvette and know that I am in the wrong area, but I also have a 79 Z/28 and have a couple problems that I thought may be the same in the same year Corvette.
With 30k miles, my 79 Z has not been driven too much the last 20 plus years. I am fixing that and have been driving it more often and I have two small problems that I need to trouble shoot.
1) After the motor gets warmed up, it sounds like I have a vacuum leak. Everything is all stock and it is a 4 speed. It gets louder when I let off of the gas and quieter under load. Listening backwards with a long skinny funnel, it seems loudest on the passenger side near the EGR valve. The vacuum lines seem tight -I even trimmed 1/4" off of one that looked stretched out. Can it be the EGR internals?
2) Though it is stock and has a whopping 175HP, it seemed like it used to get a little kick when I stomped it and the secondaries opened up -they don't seem to be opening up. I took the cover off of the air cleaner, then moved the linkage fast and they didn't open.
What is the best way to check the secondary operation?
With 30k miles, my 79 Z has not been driven too much the last 20 plus years. I am fixing that and have been driving it more often and I have two small problems that I need to trouble shoot.
1) After the motor gets warmed up, it sounds like I have a vacuum leak. Everything is all stock and it is a 4 speed. It gets louder when I let off of the gas and quieter under load. Listening backwards with a long skinny funnel, it seems loudest on the passenger side near the EGR valve. The vacuum lines seem tight -I even trimmed 1/4" off of one that looked stretched out. Can it be the EGR internals?
2) Though it is stock and has a whopping 175HP, it seemed like it used to get a little kick when I stomped it and the secondaries opened up -they don't seem to be opening up. I took the cover off of the air cleaner, then moved the linkage fast and they didn't open.
What is the best way to check the secondary operation?
Safety Car
Joined: Nov 2008
Posts: 3,720
Likes: 557
From: Seattle Washington
If You suspect a vacuum leak then I would spray some starting fluid where you think it might be. The engine will speed up or die down when You have found the spot.
The Carb is not a mechanical secondary so opening the Throttle won't open them. Its a Vacuum secondary so it needs Vacuum, and that means no leaks.
The Carb is not a mechanical secondary so opening the Throttle won't open them. Its a Vacuum secondary so it needs Vacuum, and that means no leaks.
Thread Starter
Drifting
Joined: Jun 2009
Posts: 1,287
Likes: 448
From: Upstate NY
If You suspect a vacuum leak then I would spray some starting fluid where you think it might be. The engine will speed up or die down when You have found the spot.
The Carb is not a mechanical secondary so opening the Throttle won't open them. Its a Vacuum secondary so it needs Vacuum, and that means no leaks.
The Carb is not a mechanical secondary so opening the Throttle won't open them. Its a Vacuum secondary so it needs Vacuum, and that means no leaks.
I knew that the carb has a vacuum secondary, but I thought if you hit the throttle hard with the air cleaner off, you'd see some movement?
I had the top of the air cleaner off when I was running down the road working on the vacuum leak and I could hear them open.
Thanks!
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
EGR valve is known to stick open and cause a bad idle and the diaphragm will leak just from its age. It would be wise to replace it even if it isn't your problem. The base gasket is very forgiving and very thick, so it's rare that will be torn or damaged. I would check the 4 bolts that hold the carb down and make sure they are snug. Don't tighten more than wrist tight. 15ft lbs.
Nice car!
Nice car!
