1 hour ago, jalexquijano said:

deceleration backfire not normal acceleration backfire! Totally different!

 I realize the exhaust popping is driving you nuts but achieving a light tan spark plug color should be your goal. When the plug color is right then worry about what the exhaust sounds like. Whatever is causing the problem, be it, rich mixture or back pressure you want the mixture to be right.

8 hours ago, Stanley said:

Jake Brake. Illegal in Oregon.

i wish

2 hours ago, sweatybetty said:

i wish

No ? I saw an official-looking "no Jake Brake" sign on a big downgrade there in 2001 but maybe it was a concerned resident that put it up and not D.O.T.

19 hours ago, Mark Maras said:

 I realize the exhaust popping is driving you nuts but achieving a light tan spark plug color should be your goal. When the plug color is right then worry about what the exhaust sounds like. Whatever is causing the problem, be it, rich mixture or back pressure you want the mixture to be right.

Of course its driving me nuts! Some people like that popping at the exhaust when releasing the gas pedal while  others as me do not as with the stock pipe, resonator and dynomax muffler i had previously installed it was not present. Anyway do you have a picture of a correctly tanned ngk bp6es spark plug?

THis is a picture of the former exhaust which caused no popping on deceleration.

 Google "spark plug color chart". Almost every spark plug manufacturer has one on their website. The shade of tan you're shooting for is anywhere from an Ivory color to the color of your spare tire well, to the left of the tank, in the pic above. As i stated before, the important thing is to get the mixture right first and then assess the exhaust noise. Some of the backfire may go away with the right mixture. It's also possible that the new exhaust is causing most or all of the problem with noise but you won't know until the mixture is right.

 To any and all Hitachi SU freaks out there, does anyone out there have experience running SM needles? They seem to be a common replacement but not really satisfactory, at least from what I've read.

im tired of troubleshooting the car and not getting the deceleration popping over! I called MSA and the seller says he also has a 1972 240z and has no deceleration popping at the exhaust with the same exhaust:

http://www.thezstore.com/page/TZS/PROD/15-6302

How much shall i richen the mixture so the popping goes away? im at 4 turns clockwise. Car has good power and response but still popping!

Head & Camshaft!  Even MSA says that a hot cam is for racing "Performance camshafts are intended for racetrack".  A hotter cam will not idle like a street car, its designed for output at higher RPMs!

http://www.thezstore.com/page/TZS/CTGY/classic12e03

1 hour ago, jalexquijano said:

im tired of troubleshooting the car and not getting the deceleration popping over! I called MSA and the seller says he also has a 1972 240z and has no deceleration popping at the exhaust with the same exhaust:

http://www.thezstore.com/page/TZS/PROD/15-6302

How much shall i richen the mixture so the popping goes away? im at 4 turns clockwise. Car has good power and response but still popping!

  You seem to believe that richening the mixture will make it stop popping. Where did that idea come from?

 Did the seller with the 72 and the same exhaust tell you if he had a hot cam in his engine? The cam may be contributing to the popping.

2 hours ago, jalexquijano said:

How much shall i richen the mixture so the popping goes away?

I heard the opposite: that rich mix causes popping in exhaust and lean mix causes popping through carb. But the cam might have something to do with it. Race cars always seem to be popping on deceleration.

 

1 hour ago, Stanley said:

I heard the opposite: that rich mix causes popping in exhaust and lean mix causes popping through carb. But the cam might have something to do with it. Race cars always seem to be popping on deceleration.

 Thanks for the confirmation.

@jalexquijano Start leaning the carbs out. If you think the floats are close to the right setting, set the nozzles at 3 turns down, drive it for a while and check the plug color. You'll need clean plugs to get a good reading.

damn it! now im buying a 12 NGK BP6ES Spark plugs gap them at .032, install them and race the car again following the QUICK SU DIRTY TUNING

4 hours ago, Mark Maras said:

  You seem to believe that richening the mixture will make it stop popping. Where did that idea come from?

 Did the seller with the 72 and the same exhaust tell you if he had a hot cam in his engine? The cam may be contributing to the popping.

No. I will ask my cam is a Schneider 274F and im not changing it!! Its weird it did not pop on deceleration with the former exhaust system:

http://schneidercams.com/274FL6.aspx