Intermitent sputtering and popping in the exhaust

After 4 years and over 8 thousand Kms,my trusty 426 has grown a hiccup. 4 rides ago the bike started and ran for about 15 seconds then died and it wouldn't start again. I changed the plug and it fired up and I rode the rest of the day( a couple of unusal pops on decel during the ride) Next ride it popped and sputtered for about the first few km's of the ride and then it ran good again. 2nd last ride it started sputtering right off the truck and wouldn't quit so I changed the plug and it ran fine for about 20 mins. and then it started popping again. Last ride even changing the plug wouldn't get it to stop running like S#$t!. I have gone through the carb the last few times and found nothing wrong, I have been running the same jetting for 4 years with zero trouble of ANY kind. The bike has always performed flawlessly and a quick 1/8 turn of the Zip-ty fuel screw would make the decel pop disappear. The ACV has been flipped from new and the jetting has only gone up or down 1 size depending on the coolness of the weather we ride in. All free mods have been done and the valves are set perfectly. The decomp lever has plenty of free play and as I said the carb is CLEAN. I have checked all of the electrical and believe that I have found my problem . The CDI magneto checks out in the specs but the ignition coil has .5 ohms on the primary side(.2-.3 ohms spec) and it has 22.5 k ohms on the secondary( 9.4-14.6 k ohms spec). My question before I spend the money on a 450 coil in cap is has anyone had problems with the stock frame mounted coils. Just looking for a little TT'rs experiences to confirm that I am going after the right problem to get the ol'426 running like a champ again. Sorry for the long read and thanks for any help--WR Dave. :banghead::applause:

Is my post too long or my bike too old? Nobody has had any ignition coil issues?

Not a common issue on Yamaha 4 strokes. They are pretty reliable. Check that your ignition coil is generating juice for the spark. I suspect it is at fault. :banghead:

Thanks Indy, I also suspect the coil to be the problem( weak spark producing incomplete combustion).I beleive that the high secondary resistance doesn't let the coil build up a full charge for the spark plug. I was just wondering if this was an issue that I hadn't heard about before this. As I said the bike has been totally reliable until the last two weeks. Again, thanks for the reply. WR Dave. :banghead:

After testing all the electric parts off of my buddies WR250f the problem still persists. The 250f CDI won't even spark my 426. So I am left with the conclusion that the CDI Unit is no longer controlling the advance and the spark timing as well as only giving a very weak spark signal. The only OEM chance that I have is maybe from the factory in Japan (if they have one). None on E-Bay so I guess I will be trying to see if MT racing has a Vortex CDI unit for this bike. I need this bike to last till the Aluminum WR's are available. This sucks with only a few weeks of riding left. I will have to ride a friends spare KX250 till my bike is going again(UUUGGGGHH!) WR Dave. :banghead:

Anyway, I'm talking to myself on this thread, but I just installed a Vortex X10 CDI unit on my bike today and I went to a little gravel pit I know and the bike just rips now, easier starting and while I haven't figured out which setting to use for the single track we ride, the best performance setting is very powerful and a lot of fun.No more sputtering and missing. Good Product if you need a new CDI--WR Dave. :banghead::banghead:


Check my reply to your help with the CDI question. BTW, the symptoms you described are exactly what happened to my SuperKart last weekend in Texas. I don't have much time on the unit, but I did have a ground wire come loose during practice. I was wondering if the loss of ground could have killed the CDI???

Thanks again for your help and insight.

Don E

Loss of ground can kill a CDI...

Thanks Rich. Your post confirms the same opinion that Mike at Vortex passed to me yesterday. I am almost certain that my mistake of not properly tightening the wiring harness ground wire killed my weekend in Texas. :banghead::banghead::lol:

Don E

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