Snap, Crackle and Pop

[Worty]

....... is the sound the Kwaka makes on deceleration.  Have blanked off the Kawasaki Clean Air ports, made sure the downpipes are gas tight and tried to balance the carbs as best I can, but still the Rice Crispies.  The bike ticks over nice and smooth, starts on the button, has no problems with cruising and acceleration, and the plugs are a light tan on the nose.  I think the popping is more accentuated because of the Dunstall replicas being louder than the megas that were on it.  Can't see it being a carb problem as everything else works fine.

Question is, what may improve it or is that just the nature of twin carb twins - GF never pops and crackles on decel??

Anyone else have experience of this (suppose it could be an air leak somewhere).  Does it happen on multi cylinder bikes?

Someone even suggested junking the petrol tap for a non vacuum type?

[sean]

maybe not enough back pressure in the mufflers  compared to stock ones ....I played around with a lot of different systems on my HD build and dyno numbers would change with different set ups on the exhaust ended up with a 2 into 1 system .

[Worty]

maybe not enough back pressure in the mufflers  compared to stock ones ....I played around with a lot of different systems on my HD build and dyno numbers would change with different set ups on the exhaust ended up with a 2 into 1 system .

Possible.  The stock exhausts have long gone, but the megas did have more back pressure.  However, the bike felt a bit stifled with those on, and it runs a lot cleaner with the Dunstalls.  There was a bit of popping with the megas, but it was very muffled.  It'd be nice not to have it, but I can live with it if there's no other solution.

[sean]

If the baffles are removable could try some stainless steel wool packed around them

[Worty]

If the baffles are removable could try some stainless steel wool packed around them

Er, baffles   But a good idea nontheless.  Don't mind the exhaust volume as such, but the popping only happens at decel at low speeds/revs.  If i knock it down a cog, the problem goes away.  Something to do with the tickover jetting, or something like that.

[berger]

worty scrap the foreign bag of ---- and buy a BSA ------ o i forgot you have one

[Swarfcut]

  Bangs in the exhaust on the over run were the classic symptoms of a weak mixture, also air leaks in the exhaust system can cause this. Don't ask me how, just what the books and mags said way back when.

 Swarfy.

[muskrat]

G'day Worty.
I'm with Swarfy on this one.There is either a leak in the pipes or a split in the inlet rubbers. Have you noticed it on one side more than the other?
Cheers

[Worty]

G'day Worty.
I'm with Swarfy on this one.There is either a leak in the pipes or a split in the inlet rubbers. Have you noticed it on one side more than the other?
Cheers

Definitely more on the l/h side.  the pipes have got a bit of a leak where the downpipes meet the modified silencer, but not much.  I'll seal those up and see if it makes a difference.  As for the inlet rubbers, I believe there's a method of testing using something equivalent to 'Start ya Bastard' where you spray onto the rubbers on tickover and see if there's a change in the revs.  If this is the issue, it'll explain why I struggle to balance the carbs

[Triton Thrasher]

Air getting into the pipe causes banging.

Most commonly a leak where the pipe mates to the head, or at a balance pipe close to the head. Leaks elsewhere in the system could cause it too.

A big open system can allow air back into the pipe, far enough to cause banging or burbling too.

Normally, old bike exhaust gas contains enough unburnt fuel and is hot enough for combustion to take place in the exhaust, but there is not enough oxygen.  An air leak introduces enough oxygen for the fuel to burn- Bang!

[Worty]

Air getting into the pipe causes banging.

Most commonly a leak where the pipe mates to the head, or at a balance pipe close to the head. Leaks elsewhere in the system could cause it too.

A big open system can allow air back into the pipe, far enough to cause banging or burbling too.

Normally, old bike exhaust gas contains enough unburnt fuel and is hot enough for combustion to take place in the exhaust, but there is not enough oxygen.  An air leak introduces enough oxygen for the fuel to burn- Bang!

Cheers guys.  First job is to completely seal the exhaust I reckon.  It's not too bad at present, but I'll recheck.  Can't feel any blow by at the head, but there is a bit where the downpipes meet the silencer.  I'm guessing that on throttle shut off, oxygen may be drawn back in at the blow by location.  The carb rubbers look ok, although I will test them and balance the carbs (again).  This model was fitted with loads of pipes for vacuum and clean air systems.  For those that don't know, there are two reed valves at the front of the head which allow air to enter the exhaust to burn off unburnt fuel on decel.  This has been removed and blocked off but, as TT says, air being drawn back in will cause the problem.  Will update after I've cleaned the windows for the missus