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Thought I was fouling plugs, not sure now.


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1999 KTM 300EXC stock pipe, 172 main 42 pilot. maxima castor 927 at 32:1

I thought my bike was fouling plugs. It would bog out and die just like one does when a plug fouls. I put 2 new plugs in and it fired right up and ran fine. I put a new plug in it last night and went to ride today. It usually starts first kick but it took about 10 today. I let it warm up and rode it for less than 2 minutes and bogged out and died. I checked the plug and it is perfect. Any ideas?

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I tried a new plug and it still isn't firing. I did some checking with a test light and the coil is getting power from the CDI box but the coil is not sending power to the plug. Im assuming my coil is bad. Could it be anything else.

Why isn't 927 okay for my bike?

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927 is a castor base that is more at home at high rpms and high heat like a 125 MX bike not in a 300. A full syn oil would be a much better choise at 40-50 to 1. Take your coil to a dealer and have it tested. Or check your cap and cut the wire back just a little and make a new connection or test the cap they go bad too.

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It sounds like you're on the right track. A fiend of mine rides a 1999 250EXC. He had the same plug fouling issue. I never rode it so I didn't know for sure what it was doing. I helped him put in a new top end. We started it and were going through heat/cool cycles for the break in when it stalled and wouldn't start. I couldn't figure it out. He called a friend who told him that the coil was getting hot and quitting making him think it was fouled and by the time he got a new plug installed the coil was cool, only to do it again shortly after. He ordered and installed a new coil... same problem.

Turned out his petcock was just dirty.

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switch from 927 as quickly as you can. gawd that stuff is gummy and thick. I ran out of my Motul 710, had to mix it and the 927 and they wouldn't mix. the 710 sat on top of the 927. my bike just doesn't run as well with the 927 unless I really wring it out. I run whatever I have in my weedeater and leaf blower too and they don't like the 927 either. The 927 was given to me from a friend that sold their 2 stroke.

I am glad to have a 4 ltr of Motul back on the shelf.

your issue does sound electrical from what you are describing.

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Ok, if it isnt elec then the things to check are: gas cap check valve, fuel flow to carb, plug cap loose or wire bad-cut off and screw cap back on, NEW plug, get some help to hold the plug to ground and kick to see if a BRIGHT spark. It can spark but be weak. Low compression as in the motor is worn out will cause similar problems at times.

Coils almost never go out, stators go out, CDI can get crushed and damaged in a bad crash so check the box and steering stop bolts.

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I've ohm and voltage tested everything on the bike from the stator to the plug. It all checks out fine.Right now the plug will fire. I could put the tank back on and crank the bike up and it would run fine for about 10 minutes then it would abruptly die. I could pull the plug then and it would not be firing. If I let it set for about 24 hours without touching it, it will magically start sparking again. I've repeated that process 4 times now with the exact same results every time. I've also tried 3 NEW plugs and it still does the exact same thing. Whatever it is, is something that fails when it gets warm. I've also tested everything right after the bike died and I'm getting power all the way to the coil, but nothing past it. Process of elimination tells me the coil is the culprit but from what everyone keeps telling me, that is not my problem. I'm sure by now I sound like I'm crazy and there is no way that its possible for my bike to be doing this but I promise it is.

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I've ohm and voltage tested everything on the bike from the stator to the plug. It all checks out fine.Right now the plug will fire. I could put the tank back on and crank the bike up and it would run fine for about 10 minutes then it would abruptly die. I could pull the plug then and it would not be firing. If I let it set for about 24 hours without touching it, it will magically start sparking again. I've repeated that process 4 times now with the exact same results every time. I've also tried 3 NEW plugs and it still does the exact same thing. Whatever it is, is something that fails when it gets warm. I've also tested everything right after the bike died and I'm getting power all the way to the coil, but nothing past it. Process of elimination tells me the coil is the culprit but from what everyone keeps telling me, that is not my problem. I'm sure by now I sound like I'm crazy and there is no way that its possible for my bike to be doing this but I promise it is.

sounds like it's not firing because it floods out. could be flooding out because it's losing fire...a flooded plug won't fire, will it?? I chased my tail with a similar situation and came to find out I had bad fuel. I am not saying this is what your problem is, but sometimes it's the simplest things that get overlooked.

the only way I figured my problem out was switching parts out with a friend that has a KTM, if you have one. swap out the coil, etc to see.

How much have you been riding it lately? summer richens your jetting and if you were on the rich side already, could end up fouling plugs. float level? is it sticking open?

just throwin stuff out there.

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I checked the carb and stuff out when this first started happening. Last time it died and refused to fire I put a brand new plug in the wire and grounded it at the head and did not get a spark.

sounds like you have narrowed it down to electrical. I know some electrical components can give issues when they get hot. time to start swappin out some parts or find a way to test them.

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