Popping sound from exhaust at low speed....

[CudamanTom]

Hey guys,
I'm getting a poppin backfire sound from the exhaust at low speed (1st/2nd gears). It doesn't do it revving the engine or at higher speed (15 mph and up it seems). But low speed in each gear seems to create the poppin sound. And it's exhaust for sure.
Is it timing? Is it fuel mixture? 
From a dead stop then giving gas and slowly moving when the popping begins then goes away at higher speed. Then shift into 2nd and it starts doing it again until higher speed/RPM.
Any thoughts greatly appreciated. 

thanks,
Tom

[Strawdawg]

Burnt valve?

[Chryco Psycho]

could be lean , could be timing , could be an exhaust leak .....

[CudamanTom]

could be lean , could be timing , could be an exhaust leak .....

It's a brand new exhaust. Would an exhaust leak cause a pop/backfire at the exhaust tip/tail pipe? 

[dave73chally]

Did the popping show up right after the new exhaust was installed? Was it happening before?

[HP_Cuda]

Tom

Ive been playing with timimg on my yellow cuda and I've got it to do exactly what you are talking about.

Get your timing right then then make sure your vacuum line from the distrib to carb has no cracks in it. As well make sure you are plugging your vacuum line into your carb at the right place. Holly's for example have a tuned port to plug into so at idle its low draw.

B

[CudamanTom]

Tom

Ive been playing with timimg on my yellow cuda and I've got it to do exactly what ou are talking about.

Get your timing right then then make sure your vacuum line from the distrib to carb has no cracks in it. As well make sure you are plugging your vacuum line into your carb at the right place. Holly's for example have a tuned port to plug into so at idle its low draw.

B

B,
I don't have vacuum advance on my distrib. Sorry, I forgot to mention that.
But I sure do appreciate your thoughts.
Here is my problem to add. I'm not 100% sure what my timing should be as I'm not sure of the build of the 440.

And to add, It's a very random popping at take off, low speed and low to mid idle.

[HP_Cuda]

So you are purely mechanical advance?

If so, set the timing to around 10 degrees and then slowly move up towards 16 degrees. My guess is your mechanical advance will produce 20 degrees so you will right at 36 degrees when done.

What kind of distributor and what kind of springs are you using?

B

[CudamanTom]

So you are purely mechanical advance?

If so, set the timing to around 10 degrees and then slowly move up towards 16 degrees. My guess is your mechanical advance will produce 20 degrees so you will right at 36 degrees when done.

What kind of distributor and what kind of springs are you using?

B

B,
It's an MSD distributor, not sure on the springs. What am I looking for on the springs?



And while I'm doing some researching, I'm learning that non-vacuum distribs are more for racing/strips. With this in mind and since it's only doing it at low speed/rpm, would the non-vac distrib be the probable cause? Not liking low speed/rpm but runs well at higher speed/rpm? 

B, I might try your method on the timing and see what happens but I'm wondering if a distrib WITH vacuum advance might fix the random popping/backfire.

[CudamanTom]

Did the popping show up right after the new exhaust was installed? Was it happening before?

Dave,
Sorry I overlooked your post.
This is a new (used) engine to this car and never saw it in a driving car but heard it run.
So with that in mind, I don't know what it did in a driving/moving car.

[HP_Cuda]

Well luck should have it I have the same exact setup and I put the light silver and blue springs on to get the advance curve I wanted.

So pull the cap off and see what springs are on there, you should have some spare springs that came with your distributor and they are very easy to swap out. This also depends on what kind of cam you are running, so if its a mild street setup alot of folks have stayed with 2 light silver springs.

This crazy cams folks will tend to lock the timing out and set her to 36 degrees.

I attached some photos of the MSD docs and the springs I have left to give you an idea. If that doesn't do the trick then it's time to move onto the carb.

B

[CudamanTom]

B,
Thanks for providing the info/pics. 
It appears I have two heavy silver springs installed. They don't look like the light silver spring you show pictured.
So with the two heavy silver springs, is that too much spring for street? (trying to get a grasp on the knowledge of this stuff)

And the distributor came with the motor so I don't have nay springs to swap out if I need to. I'm sure I can get some from somewhere.

Do you think the two heavy silver springs may be the cause for the popping at low speed/rpm?

[HP_Cuda]

The two heavy silver springs will give you the slowest advance

I'm sure a speed shop or pepboys sells the spring kit.

B

[CudamanTom]

The two heavy silver springs will give you the slowest advance

I'm sure a speed shop or pepboys sells the spring kit.

B

So I'm wanting a faster advance? For the lower speed/rpm?  Again, learning here.

[HP_Cuda]

Lets find out what your timing is now?

What kind of cam you running?