how to reduce popping during deceleration
 

finally ironing out my fuel issues with the 3.0l row turbo runs and pulls great . i would love to reduce the deceleration popping sound. first i probably need to understand what causes that sound and hopefully there is a way to reduce it .

in a nut shell my 3.0l built to stock with stock P&C evergreen raptor mod k27 turbo long neck intercooler original Vacuum Limiter and a 964 bov fully adjustable wur. and a boost enrichment hold out controller currently set to 4800 rpms.
i believe i have my wur tweaked correctly i have good afr # idle about 14 with a nice afr curve that runs to mid 12s just before boost low boost high 11s and full boost low 11s.

When i let off the gas the afr# jump into the upper 14s low 15s. when under a load when i let off the gas i get the popping without a load i just get gurgling.
on a side note the car is a row but i have the timing set to American settings 5 deg advanced and 22 retarded. The row settings are tdc and 26deg retarded . i have not played with the setting other than at an idle and i didn't notice a difference. would this help with the popping ?

i would love to learn more about the popping and the variance in the timing between the row and the American. ..

Thanks in advance
Regards Ned

Pretty sure the popping is just unburnt fuel igniting in the exhaust, EFI sends in no fuel when you let off throttle where CIS still allows fuel in. What muffler is on the car?

an after market stainless, the wastegate is piped into it also.

You want to do a few things to reduce popping the biggest is probably some sort of fuel reduction or cutoff.

what ecu are you using? tuner studio has a setting for it I know.

You can also advance the ignition so that any fuel that is burning has a long time to burn before hitting the exhaust. I know guys who like that noise will often retard the ignition significantly to spark it off late.

The only way you're going to get rid of it is going EFI with an overrun fuel cutoff.

1976 930 Running csi pre ECU old school .. I have a friend with a 77 similar set up not nearly as much popping.

My 76 also has a lot of popping on deceleration. I have a later exhaust where the wastegate does not dump into the exhaust. I always thought this was the reason, but seems not to be.

Push in the clutch.

Popping on decel is a function of the CIS combined with freer flowing muffler. The C in CIS stands for Continuous, the injectors will continue to flow as long as the air metering plate is raised. If you allow your engine to engine brake by not clutching during decel the extra unburned fuel will ignite in the muffler. If the muffler is free flowing you will hear the explosions. Stock mufflers mute this with all the packing, baffles and catalytic converter on those cars so equipped.
The idle bypass valve helps mitigate this phenomenon, the burbling becomes more pronounce if that valve is defective or removed.

Sorry, mistakenly assumed this was an EFI car

Thanks
newbie question is the idle by-pass the same thing as the bov? Also could a semi rich idle mixture add to this popping and and gurgling? i set my idle mixture by Backing off about a 1/8 turn from the injector squeal. A few times, when i trigger the fuel pumps from the engine bay while setting up the wur i could hear a few quick injector squeals. for a seconds then they stop.

Mine is converted to EFI and I miss the pop sound!

I did too, so i turned off the overrun fuel cut and added a little fuel and pulled some timing in the higher rpm, high vacuum cells. Now it sounds like it did before.

Perhaps an unpopular opinion but the popping is part of the appeal for me. It's old, it's raw...just like it should be

Amen!

:
I used to like it until it became a fad and all the tuners, With their cambered Honda's started purposely doing it .
Now every spring the stop signs around here sound like a war zone.The good thing it is usually short lived. The cars would be broken down and back in the garage in a month or two. :D what actually happens when you force an engine to do that what does it ruin in the motor?

My CIS 930/60 would make a lot of burble, pop, blat-blat-blat noises on the overrun, together with some infrequent (and sometimes pretty loud) backfires.

Par for the course for a CIS car, I believe. But it can be a little awkward when you've got a noisy exhaust and are trying to be inconspicuous in town....

I found that giving it just the tiniest touch of throttle on the overrun - like, literally, just off the stop - would greatly reduce popping/burbling. Apart from any other considerations/opinions, coasting in neutral is illegal many places.

The zinc plated vacuum limiter is supposed to eliminate the popping. Is the vacuum control line connected correctly? If it is original, the diaphragm has likely degraded and made it non-functional. It is testable with a little effort. The other possibility is that it is just too rich under load to compensate as adjusted.

The vacuum line is teed off the same line as by distributor and bov taken from the tap below the butterfly on the throttle body. i did test the the diaphragm with a hand pump seamed good opened and closed and held pressure . The large hose if i remember correctly is connected to the back side of the Ic and the smaller hose is connected to the large tee that feeds the wastegate taken directly off the intake manifold.