Popping on decceleration

Hi all,

When deccelerating in gear my bike makes a bit of a muffled popping / pffft'ing sound. Otherwise she runs well, idles smoothly and good throttle response.

Is this normal (I know some cars are supposed to make these sounds, but not sure about bikes)? Is it bad? Would it be due to carbs being unbalanced or perhaps too rich (too much unburnt fuel entering the exhaust)?

Thanks!

I'd look for vacuum leaks:
1.The carb boots(the rubber ducting from the air filter to the carbs).
2.The carb holders(between the engine and carbs).
3.The rubber sync plugs on the carb holders,looking for cracks
4.If you have the vacuum operated petcock,inspect the rubber diaphram for holes,and tears. Check all related rubber lines for cracks.

Also watch this:


(Using An UNLIT Propane Torch For Vacuum Leaks)

If no rubber cracks found,how's the valve clearances look? Too tight of a clearance will expand when hot, possibly causing your noise.

Also you might have an exhaust leak. The header flanges, or a small rust hole can cause the exhaust to suck some air on decell and cause some poping. Could also be simply your pilot jets are a tad lean. If you have stock pilot jets and you have an aftermarket 4-1 exhaust and or pods this might be the issue.

MFolks wrote: I'd look for vacuum leaks:
4.If you have the vacuum operated petcock,inspect the rubber diaphram for holes,and tears. Check all related rubber lines for cracks.

I had ridiculous popping and discovered the vacuum line on the petcock had fallen off! (Hence why it would only run in "Prime".)

I just replaced the carb holders with brand new ones, so hopefully they aren't the problem. Also did the spray-it-down-with-carb-cleaner-and-listen leak test around the holders and boots. Will try again with the unlit propane torch. Will also check around the vacuum line. The previous owner connected it with a hose clamp, so that may indicate a prior leaking condition.

The exhaust is near-mint, very very little rust. The header flange bolts were a little loose, so tightened those up nicely. Running stock jets, exhaust and filter.

I'm planning on pulling the gas tank to sync the carbs with my newly constructed manometer, so will pull and strip the petcock at the same time I guess.

Thanks for all the suggestions

Are you running pod filters?? Are you running Vaccum operated carbs? Could be emisssion ports need blocked?

Nope, no pod filters but I do have a vacuum petcock.

I pulled the tank yesterday and did a full vacuum leak test with both carb cleaner and an unlit propane torch ... no leaks found.

While I had the tank off I also synced the carbs with my homemade manometer.

Didn't notice any popping on my morning commute and bike sounds much better! Less noise and less vibration, better throttle response, faster idle (had to adjust the idle screw half way to work 'cause the bike was idling fast) and faster settling of the revs.

I wonder if the carbs being way out of sync was causing misfires or something during decceleration?

Going for a good ride tomorrow, so should be able to see if the problem is gone.