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Old 07-12-2013, 08:54 PM   #8097
DurtDevil's Avatar
Joined: Apr 2010
Location: Boxford, MA
Oddometer: 69
Coughing out

With the 351 and pumper carb on, for about 8 months now, the engine starts "coughing out" at around 8k rpm. Engine is smooth and responsive from down low up to 8k, and in the beginning with the big bore I was happy with that. But I'm reading that others with the 351 have the same RPM range as before... I did a few experiments and if I roll on the throttle slowly and gradually the bike eventually gets up to 10k-10,500 ... But if I accelerate hard and pin it, like I think most would do, it starts coughing .. Or skipping .. Not sure how else to describe at 8k ... Usually I back off and just switch gears at that point, the 351 gives you lots of leeway with gear selection because of available power .. But a couple times I kept the throttle pinned past 8k and the first couple "skips/coughs" and at 9k it started bucking pretty hard, it was very hard to control with loss of power and then it surging full on again-and off/on again at speed- Second run with same result was enough to convince me it wasn't going to resolve itself.
What the heck is going on? I've had three tune ups with valve checks over life of bike (800 miles, 4,800, and just a few months ago at 8,800) Always been told everything looked okay, valve clearances within range and reset to orig specs. It starts easy, runs well down low, but why is the high end not available, and what's causing that scary reaction at 8-9k under hard throttle - but not under slow acceleration? Beyond oil changes and a few basic tasks, I'm out of my pay grade and could use some advice...
2007 KLX351S, lots of farkles, even more scratches
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