Q Why won’t my R6 tick­over?

Motorcycle News (UK) - - Garage -

My 1999 Yamaha R6 has started cut­ting out on tick­over if I leave it stand­ing for a minute or so. If I get rolling im­me­di­ately it runs just fine; clean pick-up, no mis­fires, all good. But come to a halt and it just fades away, although it restarts eas­ily. Robert Mur­ray, email

An­swered by Lee Towner, Moto Works Af­ter 17 years, parts of the car­bu­ra­tion sys­tem will be get­ting pretty worn, while a tick­over prob­lem in­di­cates it’s in the pi­lot cir­cuit. Be­fore you pull the bank of carbs off, lift the air fil­ter out and have a look down through the carb ven­turis with the en­gine run­ning. The nee­dle valve de­sign in­cor­po­rates a rub­ber cone which works like a toi­let cis­tern to seal off the fuel when it gets to the right level in the float bowls. As that rub­ber ages, it al­lows the fuel to by­pass the nee­dle valve, which al­lows far too much fuel through at tick­over so it ‘floods’ the en­gine. If you can see droplets of fuel com­ing past the nee­dle valve that will be the prob­lem. If there’s none of that you’ll need to get the carbs off and give them a thor­ough ser­vice, maybe us­ing an ul­tra­sonic bath to break up any gooey de­posits in the nar­row pas­sage­ways.

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