2003 EC300 Over Reving

[prunty]

Long story short I haven't used my Gasser in about 18 months and decided I take her out to an Enduro event this weekend. So being a good wee boy that I am I thought I give her the once over to make sure she was in tip top shape, i.e. gear oil, clean filter, general check over, etc, etc...

When all was done I took her down the lane to try her out, only to notice a bit of a stutter. Decided to take off the carb and give it a clean as well to try sort the stutter. Did so and put all back together started it and it went to maximum revs, flat out and I couldn't get it turned off, kill switch wouldn't work, kicked off the plug cap, still nothing, ended up turning of the petrol and having to wait till she used the petrol in the bowl.

Anyway after a lot of messing about (hours) I decovered that the inlet rubbed wasn't sitting correctly on the intake manifold, it wasn't making a good seal, sorted this (12:30am) and tried her again only to discover that she was still reving high, albeit I had messed with the idle screw proir to discovering the fault.

Anyway I was that pissed off at this stage I just left all in a heap and call it a night. So I'm going to have another look this evening and was wondering if there is something obvious that I might be missing before I spend another evening pulling my hair out???

[stainlesscycle]

throttle cable not seated in top, or binding/not letting slide drop. air leak at intake boot, etc. carb float hung up, not letting fuel in. if kill switch won't work it's probably burning carbon from pipe and piston. it's an airleak somewhere. ignition seal, base gasket, reedbox, lotsa places it could pull air.

[prunty]

At this stage I recon is must be an air leak as well, but I haven't much experience with two strokes, apart from my wee 125 RG Gamma years ago I?m more of a Fireblade kinda guy?

Anyway I was surprised that the revs went all the way to max revs. I would have expected that it wouldn?t have started with the inlet rubber letting in air, how does it get the fuel needed when the air volume is increased with a leak??

Plus what is the best way to kill the motor when this happens, it?s very hard to stand by until the fuel runs out and her running flat out, I was afraid I was going to see a piston shooting out the side of something?

[Pepperami]

I had this and it turned out to be split carb rubber and fraid throttle cable.

[Jakobi]

If its racing hard due to a lean condition where everything is so hot that its igniting itself, then you want to add some cooling to the equation. Pull the choke and keep trying the kill switch.

If you had the carb out I'd definately be looking there again. The rubber boot between the carb and engine can get old and brittle and crack. You may have to take it off and bend it around a bit to see if its leaking. I'd just buy a new one. They aren't exy.

Other than that double check the throttle cable has free play and connected and that the slide isn't hanging up in the carb. You should be able to hear the slide clunk down as it closes on the throttle stop.

[prunty]

Thanks guy for the comments, I'd say it the inlet rubber at this stage. The throttle mechanism does seem OK in fact if you reach in through the air box you can feel the slide going up and down with the tip of the finger (I must have small hands) as well as hearing the movement.

The only problem now is that I don't think I'll be able to get my hands on a new rubber between now and Sunday and I was really looking forward to having a blast especially as it has been a while, plus the weather is excellent for a change...

[Jakobi]

I try to look on the brightside when the bike doesn't want to play for a particular ride. I like to think its possibly trying to save me from something else happening

Seriously though you will know when you take it off. If not put it back on. Make sure not to over tighten the hose clamps. Maye sure the boot on the other side of the carb is on properly too while you're at it. If you're super keen you could even pull the whole carb again. Check the bowl for any sediment/dirt. Check the slide for scratches. Double triple check that the slide and throttle cable are going together correclty with the notch on the plastic collar locating in the slide and the spring not binding. Then make sure the air boots are on properly again and bring her to life!

PS easy way of getting the carb in and out is to undo the rear air boot. Undo top/bottom swing arm bolts, loosen the opposite bottom/top and flip the whole back of the bike away from the carb.

[prunty]

Cheers. The only problem is that I'm afraid of my life starting her up again now that she's cold, if she hits full revs from cold she'll probably blow herself to bits, especially if I can't get her switched off...

[Jakobi]

You'll know immediately if the revs race and kill it. Before when it kept firing without the lead connected was because it was hot enough to continue igniting under compression.

Just double check everything and if it all looks good then you'll have to fire her up. If you find the cause then you'll know what to fix

[GMP]

The clamps on the '03s with the RAD valve were easy to overtighten and prone to distorting the rubber coupler. Also, the coupler tends to dry rot and develop fine cracks after a couple years. Very cheap and a good idea to replace every year or so when you replace reeds. Its originally a Boyesen part from the RAD valve, so multi sources there.

To avoid the distortion issue I do two things. First I clean the manifold(or RAD Valve) spigot and inner coupler surface with contact cleaner, and bond the coupler to the spigot with grip glue. Put two or three washers on the clamp screws between the clamp halves to limit how tight you can go. I made up a one piece spacer once, might still have the photo somewhere. Install carb and snug up the clamps.

Found photo of my '03 carb with clamp spacer. It also squares up the top of the clamps, as they are welded on the bottom.