I have a 2016 KTM 65sx with a Smart Carb 2, has always ran flawlessly. Last week my kid came back in mid ride and said it's running funny. Starts up and idles just fine, I have way more than enough hours on the carb setting to know it should be set up perfectly, cleaned carb, all looks well, problem still persists.
At about 1/4 throttle it starts to cut out but not quite like a bog or lean condition, I thought at first it was not getting fuel, but after cleaning everything, changing gas, and trying again the problem was still there. It seems like an irregular spark, feels like you get one good spark at random, maybe 1 out of 3 or 4 that should be happening. I tested the resistance of the ignition coil, spark plug (old and new), spark plug cap. I even bought a new cap and coil, the new ones measure the same resistance as the old. I do not have a "peak voltage adapter" to test the peak output voltage.
My next thought is stator/ignition pulse generator, but thought I would check here before I drop $200+ on one. Maybe somebody here has had the same issue and can help out, thanks!
Oh, and I checked kill switch, it's good as well.
Likely the stator, but trace all the wires carefully and look for any pinch points or rubbed spots. Open all the connectors and look for any corrosion or loose pins. Spray out with contact cleaner and compressed air.
Take the left side engine cover off and look for any obvious issues with the stator or rotor. While you are in there, grab the rotor and push/pull and check for any up/down play in the crank. The 65's have a known issue of losing the press fit in the left side crank bearing.
Make sure there's no cracks or issues with the PV actuation hose also.
I chased my tail on our 2019 TC 65 for a long time until I finally replaced the left side (stator side) crank seal. Very cheap and easy to do. Fixed the stutter I had been chasing. Might be worth looking at.
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Check that the power valve isn’t broken, the shafts break off the blade.
Here's where I'm at so far. New ignition coil, spark plug cap, stator, and cdi. None of them did anything. When I changed the stator I had to take the cap off the piston so I checked the power valve, all hoses and wires, everything seems good. I swear it's not the carburetor, but next up is to put the original carb back on, I've ran the smart carb for a year with no problem, but maybe that's it. I'll keep people posted on the solution once I find it.
Chipped reeds will cause a bike to not rev out, though your description sounds more electrical. If you haven't already, inspect the reeds.
Still trying to figure this out, bought more parts, still the same HOWEVER I did notice the last time I had the fly wheel off, there is some up and down play in the crank shaft where it is set in the main bearings. As in the shaft side that spins the stator and flywheel has play, but no oil has leaked out through the seal on either side. Seems I have to pull it all apart, but I would like to confirm if my issue is something other than this before rebuilding it and getting it all back together only to be back where I started. Has anybody had any experience where a bad bearing was maybe making the timing skip or messing with the electrical?
Thanks!
Run the bike with the stator cover off and open a propane torch (don't light it) and point at the seal. The RPMs will die down and possibly kill the engine if the seal is leaking.
I spent 8 hours chasing my tail on horrible day before Loretta’s because the yellow rubber actuator diaphragm had a small tear in it .
you can easily check yours by blowing on the vacuum line that goes to the pipe . Do it with the pipe off and watch the power valve blade go up.
If it doesn’t t move , the our diaphragm is bad .
Also that rubber diaphragm is a wear item and ruined my son’s last moto at Loretta’s the next year . He was pretty bummed at me for not changing it .
So I actually bought a new diagram and hose as well, no change. I think I'm sucking air at the crank seal unfortunately there's definitely movement at the crank that shouldn't be there. Rebuild kit in the mail now, I'll follow up if it fixes the problem, or blow up the bike if it doesn't!
@DF313 Did you ever work this out?
I'm having a similar issue w/ my boy's 2021 65SX...
But his only seems to do it at about mid-throttle.. at WOT, it revs just fine.
Gonna try replacing the PV blade completely as my next step.. Gonna also check for movement in the crankshaft as well..
Yes, my best guess is the crank bearings were bad causing air to suck in the main seals at mid rev. It probably was doing it at high revs as well, but I figure in the higher rpm the motor had enough momentum to make it less noticeable.
I did a full rebuild, new crank, crank bearings, and seals and it works great now.
I pulled the flywheel and could wiggle the crank just slightly and feel it clunk up and down, but it was so slight I almost didn't believe it was the problem. But it was the only thing left I had to try and it fixed the problem so I think it was the issue.
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