Intermittent Lean Mixture Spike

[flexibledoor69]

Hi guys, need some technical help.

I've installed a dynojet stage 1 kit about 6 months ago and all has been sweet, but now I have a very strange problem. The bike started to have a misfire when cruising around at 100kph/3000rpm mark, it was only intermittent then it would go away. I hooked up an O2 sensor to see what was happening to the mixture and while riding around normally the mixture is a little rich (around 12:1), but when it misfires the mixture readings spike up to 14.3 - 14.9 which I find a bit worrying. Give it some throttle and the problem goes away and then it might return 5-10 minutes later. Sometimes it stops spiking all by itself but i have found that giving it more throttle helps it quicker.

I'm thinking that maybe i've picked up a vacuum leak somewhere, but shouldn't a vacuum leak mean that its always running lean and not just randomly spiking on me? Any help or thoughts very much appreciated.

[lloydie]

Carb fart .

[VTRDark]

What gear are you in at that speed and revs. You might not be giving it enough beans and the engine is lagging. It's the giving it more throttle then it goes away that makes me think this. Either that or maybe lean off your mixture/fuel screws by 1/4 to 1/2 turn as the problem is low down just as you come onto the needles/slides.

I tell you what, before doing anything temporarily remove the air filter to see if things improve first, (what air filter are you running) and also make sure you have no inlet or exhaust leaks anywhere. So check the carbs are secured to rubbers with a good seal and there are no slight blows around your exhaust clamps as both these will upset things. You may also want to do a carb balance as this can sometimes cure little things like this.

(:-})

[AMCQ46]

is there an air leak from a split in the vac line........or the carb is not seated will in the rubbers to the Cyl head