KDX spoiled me for two strokes, KX60 running badly

[reepicheep]

I'm cheating here a little... my KDX is running great, but I am having problems with the kids KX-60. This should probably go in the pit bike forum, but I know the people here better :).

So say you had a KDX that would start (badly) then idle OK at low RPM (if you could get it running) and pull hard up in revs but completely cut out (like you hit the kill switch) then catch again... repeat, repeat, repeat. Its soaking the plugs also (fouling them badly). What would you suspect?

I pulled the plug, and it gets a weak spark, but it is there. If I unthread the spark plug boot and just go from the wire to the engine, I get a nice bright spark jumping a 6 to 10mm gap. So I don't think it is the coil or ignition system.

The gas is fresh, the petcock seems to flow fine, the tank vent is clear.

I cleaned the carb, no change. Jetting was fine before it started behaving badly Timing was recently adjusted and it ran fine afterwards.

It looks like it leaks a little transmission fluid out the front output shaft seal, I'll get around to fixing that someday. It's not bad, and ATF type F is cheap. ;)

I popped the cover off the stator, and it had a little dried water in there (the kid sank it up to the airbox in a puddle). So I cleaned it out with contact cleaner. It wasn't bad though, and I don't see any evidence of oil in there.

I repacked the exhaust (loosly, which is what this bike has always needed in the past to run well).

I didn't do a formal compression check, but if I stuff my finger in the spark plug hole, it pops it out fine when I turn the bike over, so its not something dramatic like a hole in the piston.

I'm thinking my next check will be carb float height, and make sure (again) the petcock is flowing OK (I'll drain the whole tank through a cofee filter and see if anything unexpected comes out). And clean the carb AGAIN. And I'll order a new spark plug boot and wire, just because the current one is like 20 years old now.

Any suggestions or other tests?

On topic for KDX, I came from a four stroke (KLR-250) to the KDX and got everything I wanted... lots more power, lots less weight, lots easier maintenance. The bike spoiled me. So I got the kid a KX-60, thinking it would be the same experience... so far it's been a fussy little high maintenance thing, though it sure has a nice suspension and runs great when running.

It really makes me appreciate the KDX... a two stroke built for reliability and tractability and long term low hassle fun.

 

[sr5bidder]

I would check the reeds out reep, then I would do a formal compression check then look at the flywheel/ key :cool:

 

[reepicheep]

Thanks! Good suggestions. I have stock reeds still in a box somewhere (swapped to Boyesens) that I can slap in there, the neighbor has a compression tester I can borrow, and the crank threads on the thing were partially stripped by a previous owner (torqued to spec, but I worry about it, and have new crank on the shelf just in case).

So those are good suggestions, and easy to whip through after I reset the float level.

Thanks!

 

[reepicheep]

Well, I am zeroing in on the problem... Nasty one, this.

The issues were (so far):
1) Fouled plug(s).
2) Aggravated by bad coil.
3) Aggravated by bad ground for CDI (a real mystery, more later).
4) Aggravated by previous owner, who put a CDI for something other than a KX-60 in my KX-60.

It was tricky. The original problem with the coil and CDI would quickly foul a plug, before the bike could even warm up. So even though you start with a stack of $6 plugs, every time you put a new one in, you are just fouling it. Go back to one of those fouled plugs (that don't look that bad) and even if you fixed some other problem, you think you didn't yet. Nasty.

The coil was bad also. I slapped in a cheap Emgo universal coil for testing, *and* a new plug, and it is running very well. Still a bit of missing at past redline, but strong right up to there.

The CDI has worked reasonably well in the past, but the wire colors are all wrong. It's a mitisubishi, so it probably came off some other Kawasaki. I haven't found one like it, but have a proper CDI on the way from ebay.

The really odd thing was a grounding problem on the coil mounting tab (which was the entire ignition grounding point on this bike as per previous owner... not sure if that is how it was intended stock). I took a dremel tool to the bracket to make sure the terminal had a nice shiny grounding point, and put the bolt (not brand new, but clean) through it so it was bolted to the bracket very tightly. Ping from there to an engine case bolt, and it comes out like 23 ohms. It should be about .5 ohms (.2 of which comes from your test leads). I don't know how this is possible for a welded on tab, but I've learned on old dirt bikes that anything is possible and it's better to end run some problems then meddle in the affairs of wizards, so I just ran a ground strap to another good grounding point on the frame. Later I may run a ground strap direct from the frame to the engine as well, it's easy enough.

So now I have to scare up a coil, and wait for the CDI to arrive. It will be interesting to see how different the bike runs with the correct CDI. Once that is sorted I can dial in the jetting.

I also found a $2 Champion plug at the local auto parts store that is almost the same as the $6 NGK that KX-60 needs (a more expensive plug than the KDX uses). Probably not the plug I would want to use for real trail riding or for the last steps in dialing in jetting, but for diagnosing problems that are fouling plugs, they are 3x cheaper to ruin. :)

Ahh the adventures of restoring old dirt bikes... :)

 

[ws6transam]

An inline fuel filter might be a pretty good investment, too. For me, it's made a night & day difference in the predictability of how the motor runs.