No top end?? Need feedback

[moto9]

So, I just ran into my first issue with the bike not running right
Here's a little info 08' ec 300 has always performed flawless, jetting pretty spot on.
The bike starts fine, idles fine, runs good until about mid throttle then starts cutting out and eventually dies out unless I back off the throttle.
Could this possibly be a bad CDI or coil...anyone have a simular problem?
I am in the process of checking the PV, the reeds and the carb...just wondering if it could be electrical??
Thanks for any input or advice.

 

[stainlesscycle]

So, I just ran into my first issue with the bike not running right
Here's a little info 08' ec 300 has always performed flawless, jetting pretty spot on.
The bike starts fine, idles fine, runs good until about mid throttle then starts cutting out and eventually dies out unless I back off the throttle.
Could this possibly be a bad CDI or coil...anyone have a simular problem?
I am in the process of checking the PV, the reeds and the carb...just wondering if it could be electrical??
Thanks for any input or advice.

doubt it's electrical. usually the cdi either works or it doesn't.

i had this exact same problem on another bike i was working on yesterday. ended up float level was too low, and bike would run out of fuel at about half throttle or under a load. i could putt around all day, but when i opened throttle under a load it would die until i let off the throttle. i thought it was the advancer/ or weak spark (points)... it would run fine on the stand. so just because it feels electrical (it was like a on/off switch at half throttle..) doesn't mean it is...

 

[GMP]

It could be electrical, especially in HI with all the wet trails, at least that I remember. Go through the coil wiring and clean/retighten everything. Check the integrety of the HV wire to the coil body and cap. Mine was loose and the connection full of water.

 

[stainlesscycle]

it sure could be electrical, it could also on the outside chance be powervalve staying closed too i would think..but i doubt that since pv is not throttle dependent..and bad reeds just get erratic results usually.

will it rev to the top at small throttle openings? will it rev out well (at small throttle and wot) in neutral on the sidestand? will it pull to the top rev ranges, up a hill with small throttle openings but not at wot? these all point to fuel delivery - main jet or float height issues..

 

[GMP]

Stuck shut PV usually gives a steady dull sound to the exhaust rather than a break up/misfire sound. Bike can run hot too.

Main jet could have worked loose and fallen out of the nozzle too. Wouldn't be the first time.

 

[wasp4banger]

I tried chasing what I thought was carburetion, spent an afternoon dicking around with main jets, ended up being the plug. I felt pretty stupid. Have you tried another spark plug yet?

To check power valve you could take side cover off and see if it is opening when you gas it.

 

[Bailey28]

Main jet unscrew itself and fall into the bowl? I had it happen on my 300 a few months ago.

 

[HuskyDude]

doubt it's electrical. usually the cdi either works or it doesn't.
i had this exact same problem on another bike i was working on yesterday. ended up float level was too low, and bike would run out of fuel at about half throttle or under a load. i could putt around all day, but when i opened throttle under a load it would die until i let off the throttle. i thought it was the advancer/ or weak spark (points)... it would run fine on the stand. so just because it feels electrical (it was like a on/off switch at half throttle..) doesn't mean it is...

I was chasing a ghost too till I sat down and thought about it. Should have check the carb last time I did a MJ change.

 

[moto9]

The bike will die out under a load, I think I can get mabye 3500 rpm's out of it but when I try to even slowly eek a little more throttle it will die out.
and it's worse under a load.

I had raced it the day before in wet conditions, water holes etc, but it ran ok when I put it away that evening.
Next morning It was acting up, I changed the plug, drained the carb but that didn't make a difference.
I pulled the pipe, PV covers, carb, the crank case dran bolt.
No water in the case, ignition cover, gas, or carb.
There was a reed with a slightly chipped corner...can't imagine that could be it.
Carb was clean, all the jets were tight,.
The PV seemed ok...I did find that the left side PV barrel has some play in it.
I will put her back together to see if it runs any better, Oh and I'll check all the electrical connections and components.
see what happens
Thanks guys...I'll let you know what I find.

 

[gasgasman]

I would go with the coil having water internally.
At high rpm its not producing a hot enough spark to burn the fuel mixture.
You can seal the coil in a ZipLock bag and set it out in the sun, you will see condensation in the bag if the coil is contaminated.

Look at the fuel cap vent for restrictions.