popping and backfiring on deacceleration
 

Hi all, I have an xtz 660 1991. Is it normal for it to backfire and pop on shutting throttle down. Any help is much appreciated, Cheers :)

Unlike the current fuel injected 660s, the old 5 valve carburettor models shouldn't pop or backfire on the overrun. However, the one I owned back in the late 90s did backfire when I bought it, but that was down to poorly sealing exhaust gaskets at the cylinder head/downpipe joint which allowed air to be drawn into the exhaust on a closed throttle. New gaskets solved this issue.

First thing I'd do is check closely for leaks anywhere in the exhaust system, but particularly close to the cylinder head.

It looks like there are no gaskets at all at the cylinderhead/downpipe joint. :( So will have to source some. Thank for the heads up, had already replaced carb o rings just in case, they looked really bad, but was still popping and banging. Cheers for the help. Will let you know when gaskets are fitted if it stops :D

That's how mine were - they had literally been eaten away and disintegrated! That was on a '94 3YF, which I bought in '99 when it was five years old. Your gaskets would be 22 years old!

FYI - There always used to be a choice of copper or aluminium (OE) composite gaskets. The aluminium ones seal better, but fall apart and the copper ones last longer but are more difficult to compress tightly.

Quick check on Wemoto and both types are still available...

Aluminium: http://www.wemoto.com/bikes/yamaha/x...uminium_fibre/

Copper: http://http://www.wemoto.com/bikes/y...ront_-_copper/

thank so much for your help, will make an order with Wemoto 2moro. Do you have any preference to copper or Aluminium? I was thinking aluminium and just change them every year or so, They are very cheap to get and its really hard to get a good seal on them so if they fit better surely its got be the better option?

That's what I would/did do! They are much easier to get a good seal.

ah, they have arrived, mighty quick service from Wemoto :) Will put them on later, will let you know how it goes :D

:( :( :( No joy, still popping and banging. Made sure they were well seated, checked joints to make sure (again) they were not leaking air. Do you think its possible that my non-factory exhaust (lazer pro enduro) is designed to pop and bang more ?? Coz I am head scratching now ..........

Sorry to hear that.

The next cheap thing to try is to check the pilot air jet/mixture screw setting. This sets mixture at idle, closed throttle and smaller throttle openings. An idle mixture that is too weak can cause back firing on closed throttle.

Standard setting is 2.5 turns out - try that first and go half a turn either way in stages and see if it makes a difference.

ah, will give it a go 2moro. Cheers :D Is it easy to get to? :/