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Help! Rough idle, stalling. Weak spark? (Read 51 times)
StripesNPipes
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Help! Rough idle, stalling. Weak spark?
05/10/26 at 21:47:10
 
Hey guys, I'm wondering if anyone has any advice or dealt with a similar issue. I have a 2002 Savage, owned for about 10 years. It ran great last fall when I put it away for the winter. When getting it out this year, it won't run right all of a sudden. The issue has changed a bit but now I'm stuck with it doing the same thing. The first time I started it, it would idle but as soon as you gave it any throttle it would die. The issue now is that when its cold, it'll fire right up but idle/run erratically. You can rev it up but it won't be completely smooth and will misfire here and there. The longer it runs, the more erratic and rough it gets until it eventually misfires more and more and then stalls. It won't run for more than about 5 or so minutes total. After that, it'll be very difficult to start again, if it'll start at all. If you let is cool down for a while or come back the next day, it'll start right up again and do the same thing. I have cleaned the carb 6-8 different times making sure everything is clear. I've also rebuilt using a genuine Mikuni rebuild kit with new needle and seat. I've cleaned the tank out thoroughly and converted the petcock to the Yamaha conversion and added an in-line fuel filter. New spark plug. I have 2 different OEM coils that test within spec and have tried both, same issue. I have ohmed the green/orange wires coming off the CDI and it is within spec based on the Clymer manual. I have tested spark after it dies and has cooled for a bit by pulling the spark plug and grounding it against the engine. The spark looks yellow/orange to me. I've tested for vacuum leaks while its running and have found nothing. I've hooked up a timing light while the bike was running to see if the spark is consistent and you can see it missing and such. Does anyone have ideas on what else to look at? I'm thinking its an electrical/spark issue but I'm stuck at this point. Thanks for any input.
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Dave
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Re: Help! Rough idle, stalling. Weak spark?
Reply #1 - 05/12/26 at 10:05:35
 
Have you checked your battery voltage?

A weak spark could indicate the battery and/or charging system is not what it should be.

The ignition system requires a voltage that is higher than what the starter can live with....sometimes the starter can function well on a voltage that the ignition system can't  Even with a good charging system a bad battery can limit the voltage (especially an AGM battery).

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Re: Help! Rough idle, stalling. Weak spark?
Reply #2 - 05/12/26 at 20:47:15
 
Thank you for the suggestion and I will double check. The battery is a Duracell AGM that was brand new late in the season last year. I just assumed it was good for that reason, but it wouldn't be the first time a new battery has failed pretty quickly.
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Dave
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Re: Help! Rough idle, stalling. Weak spark?
Reply #3 - 05/13/26 at 03:30:49
 
AGM batteries can be sneaky. Huh

I have had some last for many years, and one that failed in 2 weeks.

The last one I replaced was 4 years old and worked perfectly as I rode around doing errands one morning.  The last stop was at a friends house to visit - then when I went to leave the battery was completely dead.  It could not be jumped or charged.

The stator on the Savage is also a potential problem - they have been known to go bad....but it usually is on older bikes with high mileage.
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Re: Help! Rough idle, stalling. Weak spark?
Reply #4 - 05/14/26 at 08:31:11
 
If a bike runs fine when cold but acts up when hot, its likely not the carb (unless you see a lot of sooty smoke or smell gas in the exhaust). Its not likely to be CDI or charging system either.
More than likely its the crank trigger (pick up coil). Its located on the left side and is a hall effect sensor that looks at the alternator rotor. To test it on this bike its near impossible. The bikes that have it on the right side running off an ignition advancer you can spray it with compressed air can turned upside down (freezing cold) when its acting up and it will start working fine for a few sec. of course once its too far gone it wont run at all.
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Re: Help! Rough idle, stalling Weak spark?
Reply #5 - 05/16/26 at 00:23:49
 
It appears to be a faulty pickup coil (aka crank trigger or signal generator). There is a two-wire plug going into the CDI (green and orange wires). If you disconnect the plug and test the pickup coil side (the wires that run down behind the battery and towards the engine, not the side that runs into the hardness up towards the gas tank), the resistance should be between 200-240 ohms. When the engine is cold, mine will test within spec (around 230 ohm). Once the bike gets hot, it'll stall and won't restart right away. When I test the pickup coil when hot when it won't restart, the resistance is 250-260 ohm which is out of spec. If I let the engine cool back down until the coil is within spec again, it'll fire up. Once it exceeds the 240 ohm, thats when it'll die at idle and won't restart. But if you give it some throttle while its running and already warm, it'll stay running until you let off the throttle to let it idle and it will die again. Apparently the pickup coil will generate a stronger signal at higher rpm vs idle. The Clymer manual says if the pickup coil is bad you have to replace the entire alternator stator assembly. However, there are a few vendors that sell just the coil.
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Re: Help! Rough idle, stalling. Weak spark?
Reply #6 - 05/16/26 at 17:31:32
 
I have one of those aftermarket triggers.  It looks good and has the correct resistance.  It’s a spare that I keep on hand.  Installing it will require removal of some of the black bundle tube and you will need to splice the trigger wires, but that shouldn’t be too hard.  You will also need to pull the old wires out of the wire block where the wires pass through the alternator cover.  Be careful, you don’t wanna damage the stator.  The disparity in your continuity readings doesn’t seem too high to me, but I am not very familiar with this electron stuff.
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srinath
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Re: Help! Rough idle, stalling Weak spark?
Reply #7 - 05/17/26 at 08:45:12
 
StripesNPipes wrote on 05/16/26 at 00:23:49:
It appears to be a faulty pickup coil (aka crank trigger or signal generator). There is a two-wire plug going into the CDI (green and orange wires). If you disconnect the plug and test the pickup coil side (the wires that run down behind the battery and towards the engine, not the side that runs into the hardness up towards the gas tank), the resistance should be between 200-240 ohms. When the engine is cold, mine will test within spec (around 230 ohm). Once the bike gets hot, it'll stall and won't restart right away. When I test the pickup coil when hot when it won't restart, the resistance is 250-260 ohm which is out of spec. If I let the engine cool back down until the coil is within spec again, it'll fire up. Once it exceeds the 240 ohm, thats when it'll die at idle and won't restart. But if you give it some throttle while its running and already warm, it'll stay running until you let off the throttle to let it idle and it will die again. Apparently the pickup coil will generate a stronger signal at higher rpm vs idle. The Clymer manual says if the pickup coil is bad you have to replace the entire alternator stator assembly. However, there are a few vendors that sell just the coil.


I first ran into this on a GS500. 2 cyl with twin PU's. 1 was bad. But if I took the cover right round cover off and was moving (cant do on savage), it will run fine till I slow/stop. Then it would run on 1 cyl till I got to 20-30 for a bit of time and suddenly kick back on. Of course after a few times of that, it would not run on that cyl at all.
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Re: Help! Rough idle, stalling. Weak spark?
Reply #8 - 05/18/26 at 17:27:49
 
Aftermarket is hit and miss, but this one worked well on my 2006.  The wires are the correct length, and the wire plug that runs through the case cover doesn't leak.  OEM was stupid expensive and I gave it a shot.


https://www.ebay.com/itm/145045040616
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Re: Help! Rough idle, stalling. Weak spark?
Reply #9 - 05/19/26 at 05:51:09
 
That's a stator coil, not a trigger coil. Trigger coil is about the size of your thumb.
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Re: Help! Rough idle, stalling. Weak spark?
Reply #10 - 05/19/26 at 15:00:02
 
Yes, it’s a stator assembly but it comes with the trigger.  For that price it’s worth not having to deal with all the splicing and sealing and soldering and reinsulating etc. etc..
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Re: Help! Rough idle, stalling. Weak spark?
Reply #11 - 05/20/26 at 10:57:23
 
What DBM said.  It includes the pick-up.  If you decide not to install the stator, you’ll have a backup.  
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