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Old 01-02-2009, 12:52 PM   #1
GxB
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Angry Suspect an Ignition Problem

I've got an old '86 work sled I use for servicing remote wireless access points in the mountains.
After starting it up for the first time this winter I ran it around the yard, seemed fine, then it abruptly stopped with a very loud backfire.
Took the carb apart and cleaned it but it seemed fine, put it back together, started on the first pull, ran 10-15 seconds and then quit with a loud backfire.
Replaced the coil and plug, it started right up, then the same thing-ran for 10 seconds and died with a loud backfire.
Both the headlight and taillight quit working late last winter, so I suspected the voltage regulator was gone, but it didn't affect running the sled.
My question is this:
Would a bad voltage regulator affect the ignition circuit?
I assume the regulator is the small black box that has 2 leads coming out of it-one to the lights, one to the coil-or is that the CDI box?
Where is the CDI and would that be the likely suspect?
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Old 01-03-2009, 07:25 AM   #2
GxB
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Default Partial answer

Nothing like talking to yourself.
From looking at exploded parts diagrams it appears that the ignition circuit consists of the magneto, CDI, coil and plug, and that the voltage regulator is only in the lighting circuit. On closer inspection yesterday I saw that the boot on the intake side of the carb is cracked. Would this explain any of the problems I'm having? I wouldn't think it would, but I don't know beans about these 2 strokes. I guess "backfire" probably isn't the correct term, but when it happens it doesn't seem like a muffler explosion-seems to be more on the intake side. After the engine dies, the plug is wet. I'm assuming this would happen if spark was suddenly cut off while the engine was running and it spun to a stop with no spark.
Anyone?
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Old 01-04-2009, 08:52 AM   #3
snowmutt
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Default

Quote:
Originally Posted by GxB View Post
Nothing like talking to yourself.
From looking at exploded parts diagrams it appears that the ignition circuit consists of the magneto, CDI, coil and plug, and that the voltage regulator is only in the lighting circuit. On closer inspection yesterday I saw that the boot on the intake side of the carb is cracked. Would this explain any of the problems I'm having? I wouldn't think it would, but I don't know beans about these 2 strokes. I guess "backfire" probably isn't the correct term, but when it happens it doesn't seem like a muffler explosion-seems to be more on the intake side. After the engine dies, the plug is wet. I'm assuming this would happen if spark was suddenly cut off while the engine was running and it spun to a stop with no spark.
Anyone?
A Bad carb boot will make it run crappy. Sounds like your sucking air thur the crack This will change your mixture of fuel and air and cause it to so called ..miss fire/backfire.
Even if this is not the root cause of your problem it will do harm to the motor. Over time it will lean that side out and will melt a piston.
A way to check your spark is ...Pull the plugs and hook them back on the wires grounding the plug on top of the head,with the key on pull it over and watch the plugs for spark.
I would address the boot issue then go from there.
Your saying lights don't work...could be grounding out somewhere in the wiring, if it ran without the lights before then the electrical end of it should not be the cause of it dying on you .



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Old 01-04-2009, 12:16 PM   #4
GxB
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Cool Thanks for the reply

I will try to locate a new intake boot and replace it. I did take the plug out and rest it on the cylinder head to check spark, but the combination of bright sun, low temp and stiff wind made it very hard to tell. One of the problems is that the sled is frozen into ice-skis,track-right where it died. Not the best place to do work on it. If we get a thaw(not likely) I can get it into the shop and do some serious troubleshooting. Looks like there's no such thing as an inexpensive CDI box so I'd better rule out everything else first. Bad grounds on old machines is always a good place to look. Thanks.
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Old 01-05-2009, 04:17 PM   #5
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Cool talking to myself...lmao

the CDI is the last thing you want to change, very costly.
See if you can get someone to help you check for spark more importantly the color of the spark, if its week and orange in color you might have a coil or CDI problem if its nice and strong and blue in color you are more than likely sucking air through that boot.
you said it (the plug) is wet when it dieS, is this at high RPM?
because at high revs you would be sucking alot more air thus causing your "backfire" issue.....good luck and Happy trails
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Old 01-05-2009, 06:59 PM   #6
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Default Thanks J-Bone

Medium RPM when it dies with a bang-you know-one prime-couple pulls-starts up-rev it up and down for 10-15 seconds-bang!
The crack in the intake boot was not very serious and I taped around it just to eliminate that temporarily as a possible cause.
I probably should concentrate all my efforts on chipping it out of the ice it's frozen into and winch it up onto the trailer and get it into the shop. Pretty nasty working on these things at zero with a stiff wind. Dynamite comes to mind.
But then I remember how it's gotten me up and down some pretty rugged mountains out here to fix electronics at the top-so -maybe dynamite would be a little much. Thanks for the suggestions.
Here's some pictures from one of last winter's trips up one of our mountains:
http://www.cyberpine.net/littleyoung_charging.JPG
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Old 01-14-2009, 09:27 PM   #7
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Question Further troubleshooting...

Well...I chipped it out of the ice this weekend, towed it up to my house and got it on the trailer. Took it to the shop and got it all thawed out. First visually checked all the wiring -found a bad ground connection for the handlebar heaters, repaired that. Got my ohm meter out and checked the ignition switch, stop switch and emergency kill switch-all OK. Gave it a pull and it started right up. Ran for 10 seconds-died. Took the plug out-wet, but not flooded. Clipped a jumper from the plug to good ground, turned the lights off in shop, gave it a few yanks-no spark at all. Did some other wiring checks, returned missed calls, came back 1/2 hr. later and gave it a few more yanks. This time spark-but not bright blue-yellow/orange. Sooo...if it has fired for a while, then died, there is no spark until it sits for a while- so it seems to me the CDI is no good. It has a new coil and plug wire. It could be the magneto-but how often do they fail? I have no previous experience to go by. Can I test the output of the magneto going to the CDI with a voltmeter? Output of the CDI with a voltmeter? I assume those voltages would be 6 or 12 volts.
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Old 02-01-2009, 08:37 PM   #8
sanford
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Check the stator voltage output when the engine is cold. Leave the plugs in for a better tickover. You need to pull the recoil with roughly the same force at each reading. Set your voltmeter on AC. and it usually takes 50V Ac or more to trigger the cdi box. Look for consistant readings.If you get good readings cold before startup and no or poor after it runs and fails then the stator is defective. You may also check the coil to sparkplugs and cdi voltage to coil for its presence. Sanford
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Old 02-02-2009, 06:15 AM   #9
GxB
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Thanks Sanford. I had already put in a new coil as I mentioned, but it was a universal coil, not an OEM. A local snow machine shop had an '84 for parts and he took the coil and CDI off it for me. I replaced the coil first and it started and ran fine in my shop, so I trailored it home and ran it around. No problems. I don't know why the universal coil didn't do the trick, ut it didn't. Nice to have had it inside and warm. I replaced all the old brittle fuel lines as well and also got the lights working again. Thanks for all the help here.
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