miss fire driving me mad

[gassergrant]

Went out to a enduro yesterday done two laps and my bike had a miss fire.
i spent all the day trying all sorts of things to rectify it.
I have eliminated fueling problems changed the plug.
when i had it on the stand i could old the throttle and it would not rev and just spluttered .
I'm looking at a electrical issue, im think cap, lead, coil hopfuly not the cdi.
another one could it be the reeds, piston rings.

has anyone got any thoughts on this or had this happen

thanks grant

2003 ec 300

[Fred1956]

Check the cap to wire connection and wire to coil connection very closely for water intrusion. All CDI connectors also for looseness or moisture

[Dave]

A failed/failing voltage regulator can cause misfire symptoms.

[H0TR0Dn]

Maybe a bad/corroded ground?

[gassergrant]

thanks guys will check it asap, luckily got a friend who is rebuilding his engine so i can nick the bit to find the fault

[GasGas]

Especially since it's a 2003, I would unbolt the coil from the frame and clean all mounting surfaces and re-install the coil. Common problem with these bikes as they age. If that fails try what the others have suggested. My MC 125 had an intermittent ignition problem and it turned out to be the cdi plug, but that is more likely to cause a no start situation. Good luck!

[GasGas]

Also check that the kill switch is grounding properly to the bar. I have had that problem as well. Clean and tighten was all it took.

[moto9]

were you near lots of water?
This happend to me: at the end of day one of a 2 day race, our bikes had to be washed so their was no cross contamination between forest and the mountain.
I was so whipped after 6 hours in the woods I let a friend pressure wash my scoot.
Fired right up the next morning, idled fine, but when I throttled up to leave the start line it just missfired like crazy.
I tried every thing, drain carb, new plug, checked air filter.
well I think the coil was water logged, let the bike dry out for a week and the bike ran fine.

[gassergrant]

Hi guys thanks for all your input on this. seems that my first diagnostic was wrong, all the electrics are fine it was a broken reed valve ,it also marked the piston so going to have to replace that too so im going to have to ring up GG and see what price they go for here in the uk.


thanks grant