Just bought an 08 Rev 4. Literally just got it back from buying it. It seems to have a bit of a backfire after it has been revved hard. Is this simply an over rich fuel mixture ? I hold my hands up and say I am tottally new to four strokes. It starts fine. A I said, I have literally pulled the bike out of the van and gave it a good wash. Haven't had a chance to check the colour of the plug or see how many turns out the air screw is. Am I barking up the wrong tree with this being an air mixture problem ? Your opinion much appreciated.

regards

Gareth

Been done before mate - its not a 'problem' just 4t character and is caused by unburned fuel igniting on the overrun and will cause no permanent damage. It could be worse than 'normal' if there is air getting into the exhaust system. Seal the front to mid pipe with a heat resistant silicone.

mine developed a back fire like you discribed gradually got worse so it was banging and frapping on tick over. went to clean carb out and found the inlet manifold rubber ( from carb to barrell)had split could not see split when carb was on just fell apart when air box was pulled back. only a tenner from Birketts nice cheap fix and made it run as sweet as a nut again.

Is this a normal thing then. When i fired up the bike after washing it there was a bit of frothing between the flange of the front pipe and mid pipe so I suppose a bit of gas could have been escaping / drawn in. Does it dissapate as the bike warms up ?

As a precaution I would tend to change the intake rubber, I have heard of at least one going up this neck of the woods. It's not an expensive part (not like the twistgrips!)

Big John

after washing it there was a bit of frothing between the flange of the front pipe and mid pipe so I suppose a bit of gas could have been escaping / drawn in

as post above mate - caused by unburned fuel igniting on the overrun and will cause no permanent damage. It could be worse than 'normal' if there is air getting into the exhaust system. Seal the front to mid pipe with a heat resistant silicone.

Thanks guys for all your help. I am going to run it through the workshop this morning and give everything a good overhaul. I will silicone the mid-pipe and see if that helps. I wil have a good look at the inlet rubber too.