Top end rev sputter?

[motopsycho87]

http://www.youtube.com/watch?v=4e_H_ogPWx8

GASGAS EC300 2006

Since I've had the bike it has had a bit of a top end burble, which eventually cleared out, but now I have this. What do you reckon it is? I have changed the secondary ignition coil, new plug, ht cap etc, the carb is clean and float is correct, the bike runs just as strong as ever (even at full throttle), but right after the power valve opens it coughs and sputters and never clears out, any ideas?

 

[arnego2]

oil seal?

Hm normally I'd say the main jet could be a size too large but if you have not changed the main jet my guess would be that A the power-valve does not open completely or B your clutch side crank-seal lets pass some oil.

I lost once a pin in the PV governor on my YZ250 giving me a similar wobble at WOT.

 

[EYY]

I would also suggest checking jetting and making sure your power valve is opening fully at the correct time. Try changing your plug again too! Sounds very much like an ignition issue to me...

Are you an aggressive rider and ride it to its full potential?

 

[motopsycho87]

Had the exact same thing on a KDX200 before, it was the stator coil. I took the cover off and there was water in it and the drain was blocked, I'm guessing when I took it to the MX track the other day (hottest day of the year so far), any water inside the windings would have expanded and killed it. Runs too well at low RPM to be anything else (on the road you get about 500 rpm after the PV opens).

 

[Bodge]

Check the power valve linkage. my friend had one that would sputter and it was caused by the power valve linkage hanging up.

 

[High Lord Gomer]

I had some top end sputters from cracked reeds but nothing as bad or as early as yours.

I've also had some top end sputters when I put too heavy of a flywheel weight on a badly ported bike, but nowhere near as bad or as early as yours.

 

[motopsycho87]

Spark plug changed, Ignition coil changed, Stator coil changed, still the same. Carb is clean. It's so strange because it idles REALLY well...

 

[motopsycho87]

Spark plug - Changed
Ignition coil - Changed
Stator coil - Changed
Carb - Cleaned
Power Valve - Operating correctly
Air filter - Clean
Reeds - Checked (perfect)
Piston rings - Has very good compression on kickstart, rings and piston do not appear scuffed through exhaust

Still no idea...

 

[Rich Rohrich]

The Jetting is an obvious place to look. The possibility of a leaking right side crank seal is also worth investigating as is the grounding for the ignition system.

 

[motopsycho87]

I really can't see it being the right side crank seal, it idles far too well, and cuts out at far too specific revs...

Jetting, it ran fine with that jetting before, I rode the bike to the MX track, it was fine, did a few laps, and suddenly it wasn't revving high. On the ride home I could open the bike full throttle and it would ride until the point in which the bog comes in.

Ignition system, I am going to tear the test of the wiring out of the bike and go around each wire in tape to ensure no shorts, but I really think I'm grasping at straws with that one.

I'm starting to wonder if the CDI has failed, the power valve seems to kick in way before it bogs, and full throttle is fine at low revs in high gears...