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Deceleration popping at exhaust with new MSA Premium exhaust


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#21 datzenmike

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Posted 05 May 2017 - 04:17 PM

Unless its a normal sound from the new exhaust, its caused by fuel burning in the exhaust.  How can richening the mixture make it better???  Add more fuel to eliminate an issue with fuel burning in the exhaust...

 

Popping in the exhaust goes away when you lean out the mixture.  The info above is backward, unless its a specific carb flaw that I'm not aware of.  If that's the case, the engine would flood at idle too.  High volume air draws fuel.  A closed throttle plate stops that volume.  Velocity past the fuel port decreases with volume.  CFM (volume) is required to draw fuel, not simply velocity.  If you had high velocity air at idle, you'd either flood or have a very, very high idle.  A typical carb flows 6-10 cfm at idle, a Weber 32/36 flows around 235 cfm wide open.  At decel (6-10 cfm) the fuel in the pipe is most likely fresh oxygen.  Add gasoline and you get popping.  

 

The notion that failed ignition is the problem only adds to the evidence that's its potentially too rich already.  

 

He said he leaned out the mixture, I said richen it... back to where it should be for proper idle.

 

 

 

The BCDD (not used here) is a small carb within a carb that adds gas and air to remove the over rich deceleration. It's like decelerating with you foot lightly on the gas.

 

 

I don't see any problem here. The engine has always done this you just couldn't hear it with a muffler and resonator on it.


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#22 KoHeartsGPA

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Posted 06 May 2017 - 05:58 AM

I'd heard it can be caused by a lean condition but never understood until reading that


Yes, I went through that issue after installing the 48mm mikuni on my L20b, bigger jetting corrected the issue, if you hear the popping when you get on the gas hard followed by a loss of power, it's running too lean, you can do damage to the pistons, so get it right ;)

#23 racerx

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Posted 06 May 2017 - 07:05 AM

Out of curiosity, went on line and typed msa exhaust popping and seems like its common.

#24 jalexquijano

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Posted 06 May 2017 - 08:52 AM

I hope its common as i have already leaned the mixture to 1.5 turns clockwise and retarded the timing to 10 btdc and still pops at the exhaust when decelerating. In view of this, the lean or richen the mixture or advancing or retarding the timing at the distributor with the MSA PREMIUM EXHAUST SYSTEM will not eliminate the deceleration popping as others have recommended. Maybe one of the gaskets provided by MSA is not sealing correctly.



#25 datzenmike

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Posted 06 May 2017 - 09:09 AM

Or you're chasing your tail and it is what it is.

 


My car has no anti backfire valve, i had it removed when purchased. I have plugged all the balance tube and also removed all the emission crap! I even lowered the both gas mixture knobs  to 1.5 turns anticlockwise (leaned the mixture) to determine if the car was rich and the popping was still present on deceleration. Replacing all the spark plugs with Brand new NGK BP6ES plugs did not help. Deceleration popping still there.
 
Bottomline, the only way to muffle this popping is to go back to the original exhaust? This MSA PREMIUM EXHAUST SYSTEM comes with a Turbo Muffler while the other one was a simple Dynamax muffler.

 

The AB valve isn't a piece of 'pollution crap' so you've basically shot yourself in the foot removing it. Get another. It's job is to open during high vacuum conditions during deceleration and let air into the intake. This leans the mixture and lowers the vacuum level.


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#26 Crashtd420

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Posted 06 May 2017 - 11:46 AM

I hope its common as i have already leaned the mixture to 1.5 turns clockwise and retarded the timing to 10 btdc and still pops at the exhaust when decelerating. In view of this, the lean or richen the mixture or advancing or retarding the timing at the distributor with the MSA PREMIUM EXHAUST SYSTEM will not eliminate the deceleration popping as others have recommended. Maybe one of the gaskets provided by MSA is not sealing correctly.


How are you leaning the mixture?...
Is this just happening at idle or while driving.....
Someone please correct me if I am off but it sounds like he's adjust the air fuel screw on the carb. I believe that only effects idle and the initial transition off idle... if you up on the rpms and it's happening while decelerating you need to adjust your jetting....
A run on a dyno or an air fuel gauge might be worth looking into.... that can tell you when your running rich or lean...

#27 datzenmike

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Posted 06 May 2017 - 11:51 AM

Carb is basically at idle when decelerating. High manifold vacuum and only enough gas for idle or a small amount more.


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#28 racerx

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Posted 06 May 2017 - 11:53 AM

Have u called me a and see if its common to do the? Maybe they should of called it popping premium exhaust aystem

#29 racerx

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Posted 06 May 2017 - 11:54 AM

Meant have u called msa to see if this is common?

#30 racerx

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Posted 06 May 2017 - 11:56 AM

The if he thing too is have you asked,other z owners or join their forum and asked about msa popping noise

#31 Crashtd420

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Posted 06 May 2017 - 11:56 AM

Mike that's what I don't know so thanks...
Been doing alot of reading about tuning lately, but I have a lot to learn...

#32 MikeRL411

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Posted 06 May 2017 - 05:18 PM

Back in the '50s, that's the 1950s not the 1850s, I would tune my 49 Mercury slightly rich.  I cut the tail pipe short, welded on a "baloney" exhaust over the shortened tail pipe to the rear bumper and drilled a hole.  Inserted a spark plug [lawn mower plugs were just fine] in the hole and hooked up a Model T Ford coil [wooden crate housing and all sold by Sears], installed a push button switch to the battery.  When someone followed too closely I would speed up a bit.  If the car kept following too closely, I would let off the accelerater, wait a second and push the button.  The tongue of flame would clear all the bugs off his radiator and windshield and for some reason he would stop driving on my tail.


Edited by MikeRL411, 06 May 2017 - 05:20 PM.


#33 jalexquijano

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Posted 06 May 2017 - 06:40 PM

Well honestly my mechanic had removed the anti backfire valve, and emmission devices that where fastened to the balance tuve. He also removed the air galley. I dont know if the smog pump was removed or not by Previous Owner. I do believe so as the engine block had the blank space to bolt the compressor bracket to fasten the AC Compressor. Anyway, if i dont have the air galley installed any longer and it forms part of the emission system, even if i source a NOS Anti backfire valve if installed it would not cause any effect to avoid the deceleration popping at the exhaust. Any other way of preventing the deceleration popping at the tailpipe?



#34 datzenmike

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Posted 06 May 2017 - 06:45 PM

I think it would have an effect. When the AB valve opens, intake vacuum will suck air in. Dilutes the mixture making it much leaner. Will also drop the vacuum.


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#35 Ranman72

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Posted 06 May 2017 - 06:47 PM

a performance exhaust will have a more free flow design with less back pressure and when decelerating will be more prone to popping it is not an uncommon thing 

as mike said the stock exhaust probably did it to some extent too but was muffled by a quieter exhaust 



#36 jalexquijano

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Posted 06 May 2017 - 08:36 PM

okay! but i removed the air galley which was rotten and forms part of the emission circuit and i think i dont have a smog pump any longer. As i wrote in my last post, even if i sourced an anti backfire valve how could i make it work as it depends on the other parts of the emmision system to work correctly and those parts were removed also.



#37 KoHeartsGPA

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Posted 06 May 2017 - 09:36 PM

If it only makes popcorn while deceleration, don't worry about it anymore and enjoy the classic life!

#38 jalexquijano

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Posted 07 May 2017 - 08:03 AM

i just want to know if it will still pop if i get better pipe to pipe gaskets and manifold to downpipe gasket, replace the ones provided by MSA and seal them with red high temperature RTV gasket maker?



#39 Cheetahking

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Posted 07 May 2017 - 09:51 AM

My experience - went from a stock exhaust to a resonator only never heard a thing before, and after it pops a lot on decel.  only change was exhaust - you are just hearing it now.  The rest of the tuning stuff you are going after may be worthwhile - but won't necessarily stop the noise!



#40 racerx

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Posted 07 May 2017 - 02:04 PM

Jalex, did u get touch w msa to see see if its normal?