Re: SV650 - shooting 12 inch flames out of exhaust?
 

I would think it's too lean for a red hot exhaust.

But whether it's rich or lean there's somthing wrong with the air fuel mix.

Well if the mechanic was hired to "fit" the engine he's done just that. he wasn't asked to tune it. I don't think you have much comeback there.

Re: SV650 - shooting 12 inch flames out of exhaust?
 

Running lean can melt a piston so a red hot exhaust is no bother....

£500 to fit an engine into a buggy is a tat expensive

Re: SV650 - shooting 12 inch flames out of exhaust?
 

I can vouch that not covering up the exhaust cap on the carbs (usually used for balancing the carbs themselves) will allow you to shoot flames out of the exhaust - as hilariously inappropriate backfires. I'd recommend it to anyone (that enjoys a good laugh) and it's why I leave the tube on mine easily unpluggable and at close reach - the 'bang' switch.

I'd guess a variation of this is what's happening here - as everyone else seems to be saying - some mix of unburned fuel reaching the exhaust by a uneven mix of fuel and air entering both cylinders. Do the carbs need a balance?

Also, after that, it's likely one of the sparks has been running rich, probably meaning it's gotten all sooted up in the process if it's been run like that for any length of time. Take them out, check 'em, clean and replace.

Adrian

Re: SV650 - shooting 12 inch flames out of exhaust?
 

So unplugging the exhaust cap means more air gets into the carb system (i.e. lean) causes flames but then it its suggested its running rich?????

I give up :-dd