Exhaust popping

[Mark P.]

Just finished up my 65 project after 17 years. Took it out on the street to make sure it was road worthy so I could drive it downtown to the world of wheels auto show in Omaha. When I first started the car got one pop out of the right side pipe. Let it run for a minute or so then off I went. The motor was still cold. As the motor started to warm up it started to pop out of both sides of the exhaust. When I got back to the house it was pop pop pop. It popped during acceleration but not as bad at idle. I'm thinking I have a vacuumed leak. I see members suggest spraying flammable fluid on the carb/intake joints which will raise the rpms at idle. Any other suggestions. Mark

[Richard M.]

Re: Exhaust popping

Mark, SB or BB?

Yes could be a vacuum leak, or because it got worse when the engine normalized...

Possible exhaust leaks at the exhaust manifolds. Give each bolt a little tighten up to be sure.

I had that exact problem on a BB years ago after a season of running. I had several loose bolts.
After snugging them all up, no more exhaust popping.

Rich

[Mike T.]

Re: Exhaust popping

Mark - Back a few years when I got my 65 L78 Roadster home, I noticed it had some odd exhaust noise. Granted, there were plenty of other issues going on then but the popping was quite a bit reduced after I went underneath and found the passenger side exhaust pipe was not tight up to the exhaust manifold. One short brass nut was backed way off and the other two were barely finger tight. Tightening them up helped.
IMG_3187.jpgIMG_3200.jpg

[Chris H.]

Re: Exhaust popping

Mark, check your exhaust system where the pipes meet the exhaust manifolds and the connections by the transmission. On my 396 I had this problem under deceleration and it turns out the sleeves at the manifold and pipe connections were missing. After installing them no more popping.

[Danny P.]

Re: Exhaust popping

check Spark plugs they could be fouled up , by looking at the exhaust its running real rich ,

[Tim S.]

Re: Exhaust popping

Is it a fresh engine build? My takeaway from your post, is that it got worse with engine temp. Is that correct?

[Mark E.]

Re: Exhaust popping

Ignition timing advanced too much can cause exhaust popping.

[David M.]

not adjustable rate

[Duke W.]

Re: Exhaust popping

This thread is way off the rails. All kinds of suggestions have been offered, and about the only thing the OP told us is that it's a '65. How can anyone offer quality advice with so little information? Let's not turn the TDB into the Corvette Forum.

OP - you can start by telling us a few details about the engine, like is it one of the OE '65 engines, stock rebuilt? Modified? Or something complete different?

Since I assume it's a freshly rebuilt engine, you would have to set up the points (dwell angle assuming it's not TI) and set initial timing. What are the actual numbers. What, if anything was done to the distributor. Is it OE or modified? Have you verified that the OE centrifugal advance meets spec? If not, what is it? What is the ID stamped on the VAC?

What about the carburetor. OE? Rebuilt? Modified?

Specs are in the applicable service manuals and the AMA specs off the GM Heritage Web site.

Give us some basic information about the engine and what was done during the rebuild and some may be able to focus in on the problem rather than offering everything from A to Z.

Duke

[Richard M.]

Re: Exhaust popping

Duke,

Agreed, we need more information, but Mark has not checked in since he posted on March 8. I asked a simple question and have yet to get an answer. It's also possible his notifications are not set, or he's been tied up with other things.

I feel we've given him some things to think about based on what little information he's given us. Most answers are based on our experiences to try to help. You make a valid point we need details of his engine configuration to help triangulate on his issue.

For the record, at least we have not told him to go on Youtube for answers.

5 Days and waiting.....
Rich

[Mark P.]

Re: Exhaust popping

Gentlemen, sorry I haven't got back to you, busy at work and home. The long story on the car/motor is I started an off the frame restoration on the car in 2006. Started the motor in 2018 and had low oil pressure, finding a mouse nest in the motor. Pulled the motor and dissembled and had block dipped and oil ways cleared. Re assembled and started with 60 PSI oil pressure. Had electrical problems with motor going through 4
new voltage regulators until now car is charging fine. the motor is a 327/365 stock motor. I put hydraulic lifters in to minimize maintenance. Stock pistons, rods timing chain and gears. Has the .202 heads, stock rockers and push rods. Has the original stock distributor with tac drive. Original aluminum intake and a new Holley 650CFM replacement carb right out of the box. Has stock cast exhaust manifolds with new side pipes which were not on the car originately. Tuned the motor: idles at 800RPM with the dwell at 29. The timing is real close. When the car is running and you shut it off, then re start it, it starts right up, When I first started it there was a pop out the right exhaust . It runs cool, didn't show on the temp guage for a few minutes. So I went out for a test drive. When It started to heat up It started to pop when you accelerated. At idle and decelerated it is ok. When I got it home driving down the street it was pop pop pop. Im going out this week to test/tighten and see if I can figure this out. I will report back. Thanks for all your help. Mark.

[Duke W.]

Re: Exhaust popping

"I put hydraulic lifters in to minimize maintenance."

So what camshaft did you install?

"The timing is real close."

Can you give us the actual number you measured?

The OE Holley list number is 2818A. It's rated at 585 CFM @ 1.5" Hg depression, but some just round this to 600. It's not 650. What Holley list number did you buy?

If the distributor is assembled and installed properly the #1 wire should be in the tower immediately to the RIGHT (passenger side) of the cap window IAW the 1963 Corvette Shop Manual, and if the initial timing is in the ballpark the plane of the cap window should be approximately perpendicular to engine centerline, which places the VAC about midway between the coil bracket and inlet manifold interference points. If not, there is a problem with the distributor assembly and/or installation. A photo will tell all!

Duke

[Richard M.]

Re: Exhaust popping

To add to Duke's info here is the AIM page (UPC 6 B3) showing the distributor cap #1 configuration with respect to the window. When you get a photo of your cap & ign wires double check for proper wires placement as well, particularly #5 & #7.

DistCapWiring.jpg

[Duke W.]

Re: Exhaust popping

That AIM page shows the correct #1 plug wire position in the cap, but I disagree with the cap "clock" position. I've lost track of how many screwed up distributor assembly/installations I've corrected. (The latest one from a couple of years ago is documented here on the TDB in a thread I started.)

As I previously said the plane of the cap window ('57 to '74) should be approximately perpendicular to engine centerline. That's the "sanity check" I use.

Note that I said "approximately" since initial timing recommendations range from 4 to 16 degrees, which is 6 degrees total distributor rotation.

Duke

[Mark P.]

Re: Exhaust popping

Well I obviously need to do a lot more home work. I checked all the bolts holding the exhaust manifolds to the heads and they were tight. The nuts holding the exhaust pipes to the manifolds needed tightening. I got another full turn out of them. With the car running and warmed up I leak checked the intake manifold and no leaks. I installed a new set of points and set the dwell at 30. Had the same problem. I am going to pull the distributor out and take it to a someone who knows a lot more about it than I do. Ill let you know what I find out. Thank all for your help. Mark