ec 300 sudden power loss, wont rev

[Fastboysparky]

Ok, I have read lots of threads on this but still puzzled. I was on a very bumpy section with lots of loose rocks, I had the throttle pinned going up the gears, the bike was riding it well, I could hear the rocks battering the little gasser but I was having fun. I slowed down to turn onto wet muddy grass and opened her up again, nothing, she was totally flat, no power band. I immediately thought i had crushed the pipe so I stopped to check. It was fine. I have now checked the following
Stripped and cleaned the carb, twice.
New plug.
Removed pv cover and checked for operation. Ok
Checked silencer for blockage.
Checked base gasket for leaks.
Checked reeds.
Checked carb to inlet rubber for perishing and holes
Rode it with ckoke on and off.
Rode it with fuel switched off (till it stopped)
It had new crankcase seals not long ago and oil level is fine
Fuel and oil ratio is as always.
Checked connection to cdi and coil.


When I hold it wot on the road, it gets to certain revs and acts like its stroking, it sometimes tries to go if I wind back the throttle. I am close to trying a match in the petrol tank, it wont fix it but it will make me feel better.
Can anybody help, please.

[memphis2857]

Check for a broken reed?


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[2taddict]

"Maybe" check the pin that holds the connecting spring to the PV actuator plate has not broken off. Behind cover on R/H side of the cylinder. I just had this problem myself and that's what I found. It was still working to a degree but the exhaust valve was not opening enough when on the gas.

[Fastboysparky]

I have checked reeds, they are ok.

[barossi73]

faulty cdi?check insulation on ht lead for chafing?

[Tigger52]

Sounds exactly the same as when the pin on my power valve actuator snapped off

[Fastboysparky]

Just checked the power valve again, looks fine to me. There is a steel wire coming up from engine that moves the pv. This is connected via a locknut, then there is central bolt holding plate to pv spindle. Should there be anything else. It moves to full open as soon as you crack the throttle. Then bounces back when I let off.


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[Fastboysparky]

I have attached an image. Needs a good clean.



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[VxZeroKnots]

Looks like it should other than all the black goo.

I'd check the input on the coil again, a poor connection there is what caused similar symptoms in my bike.

[Fastboysparky]

I am borrowing a coil, regulator and cdi/ecu tomorrow from a fellow gas gas rider. Will try each one individually. Gonna get rid of the engine map switch then cut off all shabby looking wiring connectors and solder wires together. The bike only has daylight MOT cause the light and loom are shot.


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