EC300 won't run properly
 

Hi all, I've got some issues with my '04 EC300, I'm after any hints on where I should start looking. (I've asked this question on dbw too, for those that frequent both forums - it's not deja vu)

Over the last couple of rides I've noticed it's just not running right in the top end. It misses a bit and the power just falls away. A bit of testing found that it's really whenever I use WOT. Midrange and bottom end felt nice and strong, up to about 3/4 throttle. Changed plug and cleaned out carby with no results. Last couple of rides it's also been fouling the plug a bit after any more than a couple of minutes low speed riding, taking a few seconds blast to clear up and get going again.

Riding today, halfway through the ride it just died like it ran out of fuel. I got it started again and limped home, but it would only run properly at light loads and lowish revs. As soon as it got a gob of throttle it'd die like you were holding the kill switch. It would free rev well enough but not if the throttle was snapped open.

It's back in the shed now waiting for me to start looking at the thing. Any tips on where I should start looking?

It's not clearly electrical or fuel to me. The WOT problems earlier in the day suggest carby or perhaps reeds? But the behaviour that developed later in the day suggest ignition, since it seemed related to load rather than anything else. Perhaps there's two separate problems?

Fuel problems and spark problems can feel so similar that it's sometimes hard to tell which one is the issue. Rich fuel or lack of spark will cause plugs to foul and missing or cutting out under high rpm or high load situations.

It sounds to me like you may be dealing with a weak ignition or secondary ignition breaking down. Checking the plug wire, plug boot and ignition coil for carbon tracking would be a good place to start.

Plug gap....
Plug chop

Petcock good? flowing enough fuel?
Float level?

Check rear muffler.The inner perferated tube can break and cause a blockage.Do a repack while your there.

Checking all connectors etc and resistances of the ignition components might be a good start too then.

Different plug was tried, gap was good, no change in results. Nothing odd to me about plug colour or condition. Plenty of fuel (based on the amount that will pour out of the overflow if the bike is leant over). Float level doesn't seem likely to me because it dies the moment the throttle is cracked open. My experience with float level problems before is that it'll get going well initially and then die soon after.

Muffler is an interesting one, exhaust note didn't change at all and it does get regularly re-packed, but I'll definately take a look.

i would check the float bowl man. fwiw pop that main out.

Well so far, the stator and exciter test fine iaw specs. Exhaust looks fine.
Can't find any specs on the CDI unit itself to test that.

Couldn't find any specs on the coil either.
The spark plug side of the coil measures 6.16k-ohm between the HV output and earth. The input side measures 0.4 ohm to earth. The lead is 5.27k-ohm. Do these figures sound right?

A number of the connectors looked like they had a bit of corrosion, I've cleaned them up. Haven't tried it out again yet. I get along too well with my neighbours to sit there reving my bike in the shed at 10pm...

Carby out next I suppose.

Have you checked compression?

Compression feels good (unchanged) just based on the kickstart force. Haven't done a proper compression test.

I had a very similar problem with my 05 300 a couple of years ago and it actually was the carb. The main needle had wollered out the inside of the carb from vibration and was causing it to not run properly on the high end and was fouling plugs. I tried everything new plugs, cleaning the carb several times, checked all connections and after all that I call Les Tenious (LTR Racing) and he had me check the carb for wear from the main needle and sure enough that was it. I replaced the whole carb and it runs pefect now but found out I could have just re-worked the carb and put a larger needle in it and it would have worked. I don't know if this is the problem with your bike but just something to check.

GHill