Been awhile since I made a post here. My 220 has been running excellent for the past year or so. Suddenly, it started to run rough. I I had just got fresh gas and cleaned and oiled the air filter. I’ve already tried different gas and a different filter in the problem still happens.
Checked the operation of the KIPS
Checked silencer packing
Tried a new spark plug
Borod cylinder. Great shape
Checked cleaned carb, jet block o ring is sealed
Still starts up in one to to two kicks, but it’s hesitating under light throttle and just overall running rough. The bike seemed off that day, but I had confirmed there was something definitely up while riding at high rpm WOT and feeling the sputtering/ or misfiring. When I got back and tried a different filter to verify whether I overoiled, it was sputtering worse at wot. The next day, after trying the other things in my list, it stopped doing It high rpms, but it was just overall running rough with a weak idle and lack of smoothness, crispness. So right now it’s intermittently missing everywhere under light throttle/acceleration and not performing up to par on harder acceleration. It has been running the best it ever had prior to this. I’m definitely not getting any air leak vibes or anything major mechanical. I’m wondering if this is some type of electrical issue I feel like I felt this before and I thought I fixed it by going down on the jets, but I wonder if that was just a coincidence if there’s some type of intermittent fault the bike shows from time to time. Another interesting thing I found is when I turned the headlight off the idle jumps up I turn it off. The bike idle is low enough to the point it wants to die. Typically the extra load on the engine with the headlight on doesn’t make a very noticeable difference as I’ve studied in the past. But like I said, it’s been going strong for a year now. I have about 40 hours. Any ideas? Thanks
Re: Sudden rough running
Posted: 05:54 pm May 12 2026
by Chuck78
I'm sorry to hear of your current running problems, but I'm sure you will get it figured out. After swapping in a good-known spark plug after testing it for resistance to see that it is around 5,000 k after scratching the surface to get a good continuity connection (I've been finding a lot of bad NGK spark plugs in the past 2 years, their quality has gone downhill severely), I'd ohm out the ignition stator source coil and the high tension ignition coil. The high tension spark plug coils don't readily seem to fail on these at all, that would be the last thing I would suspect but it is possible.
Swap CDI from another KDX if all else fails.
I'd be highly suspicious of the ignition system health, spark plug and stator coil would be the first suspects. The CDI boxes are aging electronic components that are only good for 20 or 30 years typically, the capacitors at least, so there may be an issue in that as well, the output transistor/capacitor? They're not easily serviceable, as you must dissolve the epoxy potting just to access the circuit board componentry as I have learned through Jaguar (Michael Forrest).
I hope you get this one solved quickly, best of luck
Re: Sudden rough running
Posted: 10:34 pm May 12 2026
by JZ05220r
Thanks Charlie, I definitely won’t stop until I have it figured out, that’s for sure. I’m just not savvy when it comes to electronics. Jeff Fredette said to replace the ignition coil. I will test the spark plug as you described. Do you know the solid replacement for the source coil? I know a longtime member on here Slick Nick rewound his at home and had excellent results.
Re: Sudden rough running
Posted: 11:31 am May 13 2026
by Chuck78
JZ05220r wrote: 10:34 pm May 12 2026
Thanks Charlie, I definitely won’t stop until I have it figured out, that’s for sure. I’m just not savvy when it comes to electronics. Jeff Fredette said to replace the ignition coil. I will test the spark plug as you described. Do you know the solid replacement for the source coil? I know a longtime member on here Slick Nick rewound his at home and had excellent results.
Yes, I have red Nick's rewind posts. The ignition source coil wiring is much thinner than the lighting stator, so perhaps it's a little more tricky? I have not done either myself but may at some point in the future.
Ricky Stator is generally regarded as the best source, the other one would be a rewind from Rick's Motorsports Electrics. Take note that these are completely separate businesses, as is RM Stator a separate business from those two (RM Stator is generally all imported products mostly from China, with their name slapped on them).
With similar names, it can be confusing when discussing these three different companies that sell similar products.
When you say ignition coil, are you referring to the stator coil? Or the high tension coil that the spark plug wire is connected to?
I would go OEM on the high tension coil.
Re: Sudden rough running
Posted: 01:05 pm May 13 2026
by JZ05220r
Yes I am referring to the high tension coil.
Here is a video of me putting around in second gear. All I had time to do yesterday.
Re: Sudden rough running
Posted: 08:32 am May 14 2026
by JZ05220r
Source coil resistance: 290 ohms
Ignition coil primary: .2 ohms, some dipping into .1 ohms
Ignition coil secondary: 5.95 K ohms
Still going to try a new ignition coil and new KX100/250/500 spark plug boot. The OEM part number is discontinued for the KDX220 but looking at used and new listings of the KX 100 spark plug boot, it has the same part number stamped on it. Have no idea where to look after that. My float height did get lower/leaner ever so slightly since where I last left it based on photo logs but I’m not going to attribute that to this dramatic change in performance/smoothness.
I did take a peak at the reeds with my borescope through the carb holder boot. Nothing alarming seen from that vantage point.
Re: Sudden rough running
Posted: 09:49 am May 16 2026
by JZ05220r
JZ05220r wrote: 07:48 am May 12 2026
Been awhile since I made a post here. My 220 has been running excellent for the past year or so. Suddenly, it started to run rough. I I had just got fresh gas and cleaned and oiled the air filter. I’ve already tried different gas and a different filter in the problem still happens.
Checked the operation of the KIPS
Checked silencer packing
Tried a new spark plug
Borod cylinder. Great shape
Checked cleaned carb, jet block o ring is sealed
Still starts up in one to to two kicks, but it’s hesitating under light throttle and just overall running rough. The bike seemed off that day, but I had confirmed there was something definitely up while riding at high rpm WOT and feeling the sputtering/ or misfiring. When I got back and tried a different filter to verify whether I overoiled, it was sputtering worse at wot. The next day, after trying the other things in my list, it stopped doing It high rpms, but it was just overall running rough with a weak idle and lack of smoothness, crispness. So right now it’s intermittently missing everywhere under light throttle/acceleration and not performing up to par on harder acceleration. It has been running the best it ever had prior to this. I’m definitely not getting any air leak vibes or anything major mechanical. I’m wondering if this is some type of electrical issue I feel like I felt this before and I thought I fixed it by going down on the jets, but I wonder if that was just a coincidence if there’s some type of intermittent fault the bike shows from time to time. Another interesting thing I found is when I turned the headlight off the idle jumps up I turn it off. The bike idle is low enough to the point it wants to die. Typically the extra load on the engine with the headlight on doesn’t make a very noticeable difference as I’ve studied in the past. But like I said, it’s been going strong for a year now. I have about 40 hours. Any ideas? Thanks
Re: Sudden rough running
Posted: 09:57 am May 16 2026
by JZ05220r
Went to my local advance auto parts purchased another new NGK plug. Got back, trimmed a little off spark plug wire for a fresh connection. Clean the threads out in the frame where the ignition coil mounts and the three ring terminals were sanded. It’s back to running great again. So either I had a bad connection somewhere or the new spark plug failed right away. Hopefully it stays this way for awhile now. Going out for a few hours today.
Re: Sudden rough running
Posted: 11:10 am May 16 2026
by Chuck78
JZ05220r wrote: 09:57 am May 16 2026
Went to my local advance auto parts purchased another new NGK plug. Got back, trimmed a little off spark plug wire for a fresh connection. Clean the threads out in the frame where the ignition coil mounts and the three ring terminals were sanded. It’s back to running great again. So either I had a bad connection somewhere or the new spark plug failed right away. Hopefully it stays this way for awhile now. Going out for a few hours today.
I've had such significant troubles with NGK spark plugs in the past few years since they are not fully made in Japan any longer, and there exist so many fakes/forgeries of NGK plugs, that I am considering switching to Denso Iridium plugs again. These were all bought from motorcycle shops and Auto Parts stores, mind you, not Amazon or ebay or any other potentially questionable sources, they're just outsourced nowadays and manufactured parts from various countries outside of and including Japan.
I prepped my '77 Suzuki GS750 for a massive road trip Ohio to Colorado and Utah, and did it last minute, and I decided I was going to change the main jets ahead of time for the high elevation as I wouldn't really be running hard on the commuter trip 1,350 miles Ohio to Jamestown Colorado, and I lower the needle a half clip position using 0.020" spacers, as it was previously running too rich even at 1,000 ft elevation. Cleaned the carbs, reinstalled, put in fresh spark plugs for the trip, packed up after firing it up and hearing it idle.
Left the next day in between torrential downpours, once we hit heavy rain very shortly in, the bike wasn't running great but I just assumed I was taking on a lot of water into my exposed open element K&N air filters.
A couple states later after things had dried up, my bike was still running poorly. I thought, wow, for just light throttle, I didn't think the main jets would affect it that much... Pulled 1 plug to read, and it surprisingly looked good... On a time crunch with leaving only one day margin (3days) on what's typically a very long two day ride, I just plowed through.
I spent a lot of time fiddling with jetting in Colorado, and it never ran right the whole trip, major bummer being in the Rocky Mountains with a very performance oriented 844cc bike now running as if it was a 350cc...
I didn't think to check the new spark plugs... SMH
When I got home, pulled them out and found the following (quoting myself from a previous write-up):
(These are not 5,000 ohm reaistor plugs, FYI, but now all you can buy are the KDX version of these which are 5000 ohm resistor plugs, and the resistor plugs are less reliable, keep that in mind... Two more failure points on either end of the internal resistor)
I ohmed out the coils (✓ok), & ohmed the four NGK B8EGV plugs I'd had on the shelves new in box for a few years that I'd ran for this trip.
WOW. It "had spark" on all 4, just ran very weak on the bad plug under load/compression/RPM.
So I swapped them for the very last unopened 4-pack batch of NGK B8ES plugs from my stockpile, & ohmed them out for reference, before installing...
1.0 ohms
1.4 ohms
4,100 ohms
24,000 ohms
BRAND NEW IN BOX!!!
I scratched the surface plenty to try and get a better connection for my meter leads, no change.
Time to switch back to Denso Iridium plugs I suppose, to see if they are any better.
Michael Forrest aka Jaguar has resorted to what was formerly known as a downgrade going to Champion spark plugs from Japanese plugs, due to these problems with the Japanese plugs that were once far superior to the (formerly?) American-made plugs....
This problem is not unique to our bikes and is not unique to even spark plugs, aftermarket parts for everything are just going downhill in quality and have been for a while. While older vehicles may be far more reliable than modern vehicles with all their computer control circuit boards and lower quality components, the crux of trying to keep an older more reliable vehicle and good condition would be the quality of the replacement parts that are available for it if you cannot get the OEM....
Re: Sudden rough running
Posted: 04:43 pm May 18 2026
by JZ05220r
Yeah, definitely a big problem. I run the NGK BR8EG. Not too sure what the proper replacement is yet. I am friends with “Jaguar” on Facebook he refreshed my memory on the whole spark plug thing. I ended up not taking his advice and try a Champion plug. Like I said if it was the new plug that fixed it than my first replacement was trash. Would have been nice to know for sure but honestly, at least I don’t have to worry about fixing it anymore.
Re: Sudden rough running
Posted: 08:07 pm Jun 13 2026
by JZ05220r
Just had the kdx out today after it had been fine for a good bit after fixing the original problem. Now it’s still running like normal everywhere EXCEPT it has a high rpm misfire/wont rev out fully. Unsure of what’s going on. Might start by trying a fresh batch of gas and go from there but it’s irritating to be revisiting a similar problem yet again. Coincidentally I did clean and oil the air filter once again recently and only had the bike out in the yard for a 1/2 hours before today’s ride at a local spot.
Re: Sudden rough running
Posted: 08:51 am Jun 14 2026
by ss109
Check those same connections you cleaned before and make sure the plug wire is still making a good connection.
Re: Sudden rough running
Posted: 11:15 am Jun 14 2026
by JZ05220r
Yesterday I only rode for about a half hour at the spot and then parked it once I noticed the sputtering at high rpm. I then parked for about three hours and tested on my land with a new plug through the gears and it was still doing it after multiple pulls.
Today, I checked all the connections, dumped my tank of fuel out into another can and put fresh fuel in. It did not have any issues whatsoever and was ripping through the gears great and hanging on at high rpms without issue. Weather is almost identical yesterday’s weather. Maybe it’s a bit more humid at 86°F.
Whatever I guess I’ll just keep an eye on it, but for now it was fixed
Re: Sudden rough running
Posted: 05:05 pm Jun 17 2026
by JZ05220r
Well that didn’t do it, it’s intermittent. Yesterday I rode it and noticed it again. It didn’t do it after trying to recreate it by doing more wot runs. I’m at a loss. Today it did it everytime out of my 3 wot runs.
Re: Sudden rough running
Posted: 09:31 am Jun 18 2026
by tosaw
Intermittent sounds electrical, start by checking grounds. Try an iridium NGK, I haven't heard of those being faked yet and I've had great luck with them in many bikes over the past three decades. My next guesses would be CDI or Stator.
Re: Sudden rough running
Posted: 03:33 pm Jun 18 2026
by JZ05220r
tosaw wrote: 09:31 am Jun 18 2026
Intermittent sounds electrical, start by checking grounds. Try an iridium NGK, I haven't heard of those being faked yet and I've had great luck with them in many bikes over the past three decades. My next guesses would be CDI or Stator.
Thanks for the advice. Ill throw an iridium plug in at some point and see if that makes a difference.
Re: Sudden rough running
Posted: 03:40 pm Jun 18 2026
by JZ05220r
Here’s a video of the issue. 1st is a short video showing the issue most clearly.
This video is uncut as some of the pulls weren’t as discernible..
Re: Sudden rough running
Posted: 10:40 am Jun 19 2026
by JZ05220r
Looks like I’ll be replacing the source coil. I’m torn between wiring in a new aftermarket one (I’ve heard problems about aftermarket ones) or just purchasing a used stator assembly
Re: Sudden rough running
Posted: 01:21 pm Jun 27 2026
by JZ05220r
New used stator assembly. Same issue. Thinking of trying a new rm stator cdi. Not too many more ideas besides trying to change the reed petals.
Re: Sudden rough running
Posted: 02:53 pm Jun 27 2026
by Chuck78
Have you inspected the reed petals? How's your air filter condition and sealing, as well as oil content?
