Hello from Paisley, Scotland.
Just found this forum today and joined in the hope that you can help me.
I've just bought a Derbi Mulhacen 660 which is fitted with an XT660 engine.
It's not right just quite running right and stalls on occasion.
The spark plug colour is white rather than a "rich tea biscuit" colour - it looks like she is running lean.
I've heard that you can adjust the CO level / Fueling which you do through the dash?
Any help that you XT owners could give would be greatly appreciated.
Cheers Craig

Hi
Try use the search function because a lot of this have already been mentioned before. I dont know how the dash works on a Derbi but you could try the same procedure as for XT.

To help with the stalling try adjusting the CO, set idle to 1500 rpm and by a O2 controller from kev if it compatible.

Another thing is that you can't read much from the spark plug these days because of the high ethanol in the gas which always make the spark plug look lean. 5-15% blend here in Sweden makes the spark plug not truthful. Finland, Germany and French have up to 10% and i think you have 5%?

Ethanol is an alcohol and alcohol separates from gasoline (called Phase Separation) in a relatively short time. In doing so, the alcohol attracts water molecules and gasoline sitting in holding tanks, gas cans or your motorcycle can become diluted. As the contaminated fuel mixes with the same amount of air as before, your engine is forced to operate at a lean condition. Running lean means hotter operating temperatures which can cause an increased wear factor for your spark plugs. In addition, the diluted fuel has a reduced octane rating that may cause your engine to �knock� due to predestination. Some common engine problems associated with E10 Gasoline include:

• Lack of Performance
• Loss of Power
• Hard to Start
• Doesn�t Want to Idle
• Hesitates on Acceleration
• Stall at Slow Speeds

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XTX 2011. Yamaha Hand Guards, Akrapovic slipon mufflers, Snorkel removed, Airbox drilled, AIS Blocked, PCV, Dynojet Autotune, Kev O2 Controller, Dna Stage 2, KN air filter, mini indicators, steel sprocket cover, cnc levers, cnc mirrors.

Please send a private message to Kev our in house mechanic guru, he will sort you out with a fuelling mod, but he needs to ask you a few question to find out if your bike has a Lambda probe on the exhausts headers or not because if it has, then you'll also need an O2 eliminator or the mod itself won't work. Speak to Kev, thank me later