popping thru exhust when i let off throttle

Hi I went thru my carbs after a rebuild and put headers and short mufflers about 14 in long with turn down tips with a k&n filter in the air box I left the stock pilot jet and and went to a 125 main and shimmed the needle with 2 - 3mm washers the bike runs good with good acceleration tops out at 8500 but im popping when ever i let off it im wondering if its the carb or the shorty mufflers causing it. at night it does sometimes shoot a little flame out when it pops thanks for the help
82 kawasaki kz 750 csr twin bs34 carbs

Could try enrichening the fuel mixture with the pilot adjuster screws.
Often reduces popping on deceleration.

Good Luck!

One other thing can cause this. Do you still have the air-injection stuff on the valve cover? If so, when the control valve stops working, you get backfires through the exhaust on deceleration.

The easiest way to test it is to cap off all the connections to it. There should be 2 small vacuum hoses to the intake manifolds, and two large hoses connected to the top of the valve cover. There is also one big hose to the air box.

Plug the ports the vacuum hoses went to on the intake.
Plug the two ports on top of the valvecover.
Plug the hole in the airbox.

I'm not positive on the hose count for the twin, but at least on the fours, there are two vacuum hoses.

i have pilot screws 2 turns out from close were would you recommend

ok ill try to plug the lines to check it out i have my pilot screws 1 1/2 turns out

i tried to plug the lines did not help i opened my pilot screws to 3 turns out that helped a lot took away about 60% of the popping whats the most you can open the screw up

Am unsure about pilot screw adjustment on these particular carbs (thinking CV), as to which direction is leaner and which direction is richer. Appears in this case that turning out serves to enrichen.

One full turn out from 2 to 3 is very significant. Don't want so rich that idle speed suffers or plugs foul at lower rpm operation.

Was going to suggest enrichment turning in 1/8 turn steps.

Might also first set pilot screws for best low idle. Then go 1/8 turn richer, and test ride.

Perhaps a larger pilot jet might be helpful, if available for these carbs. Or at least assure existing pilot jets and pilot circuits are clear and clean.

Good Luck!

If not already done, would also assure no air leaks in carb holders or vacuum sync nipple caps, and that carb holder clamps are snug.

Good Luck!

I just went thru carbs and cleaned every port and passage with carb cleaner ans thin guitar string after i acid dipped all the parts i have checked for air leaks by spraying starting fluid all around carb at idle with no change they do make a larger pilot jet stock id a 45 i found a 50 online i thought pilot was mostly for idle thou ill try to change it if you think it will help will a poor sync cause the popping i did it with a cheap guage

killerkaw wrote:

I just went thru carbs and cleaned every port and passage with carb cleaner ans thin guitar string after i acid dipped all the parts i have checked for air leaks by spraying starting fluid all around carb at idle with no change they do make a larger pilot jet stock id a 45 i found a 50 online i thought pilot was mostly for idle thou ill try to change it if you think it will help will a poor sync cause the popping i did it with a cheap guage

Imo, sync (good or poor) has little if any effect on the popping, whereas pilot circuit and pilot circuit fuel mixture, including size of pilot jet, may have a significant effect on popping, especially during deceleration.

The pilot circuit influences performance during first 1/4 throttle, including idle, then becomes gradually less influential as the throttle slide, needle jet and jet needle assume command during 1/4 - 3/4 throttle.

Imo, the larger pilot jet should help reduce the popping.

Good Luck!

ok ill order the larger piolot jets and try that and let you know if it works