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KTM 250 SX won't start after fouling plug.

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Ok I just bought a 1999 KTM 250 SX. I brought it home and ran it for about 45 minutes and it ran decent but was boggy in 1st and 2nd gear and had a hard time hitting power band. It also didn't like to rev up in neutral very easy. Kind of shot a lot of smoke out. But didn't smoke that much at all once I had been running it for about 5 minutes or so. 3rd gear and up it pulled pretty strong and would lift the front wheel up.

 

 

After the first 45 minute ride, I put the bike away for about 15 minutes, took it back out and started it up. It shut off within about 45 seconds of riding it. Just bogged out. I assumed I fouled a spark plug. Took the plug out and it was black and wet with oil. Swapped the plug with a new one and rode it for about 10 minutes and it bogged out again while I was riding it. Put a new plug in it, and it wouldn't start at all.

 

I then checked the float level, it was way out of spec. Adjusted it to what I think is the proper setting. And it still won't start. It has a new plug, fresh gas, air screw at 1 1/2 out. Carbs sparkly clean. Air filter clean. Float set right. Gas mixed at 1/50.

 

I decided maybe I got a faulty plug, went and got a new one. Found out the 3 other plugs that were in it were the wrong type? They are b9es. The one that my bike calls for is BR8ECM. So I bought the BR8ECM and put it in, bike still won't start.

 

Some one help, I've been trying to get this thing started forever.

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sounds like it hot seized, pull it apart and check out the cylinder and piston. Both could need replacing

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Hot seized? What makes you think that? The bike ran about the same after it "Fouled" the spark plug the first time. And it sounded the same the second time it bogged out and died as it did the first time. The piston still turns over and every thing.

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What would the best piston kit be for the bike? It's a 1999 KTM 250 SX. Where should I buy it also? And what all is needed for the top end?

 

I have replaced a top end on a yz 125 before so I know how to do it. I just forget all that's needed.

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What would the best piston kit be for the bike? It's a 1999 KTM 250 SX. Where should I buy it also? And what all is needed for the top end?

 

I have replaced a top end on a yz 125 before so I know how to do it. I just forget all that's needed.

Piston, rings, circlips, wrist pin, wrist pin bearing, gasket set, 2t oil...and some tools. Look up Cooksey, I haven't used him yet, but his prices seem good and he'll be able to send to everything in a kit.

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Cover the basics before you start tearing it apart.

 

*pull the plug, put it in the plug cap, lean it against the head so that you can see the gap. Cycle the starter and check for a spark.

 

*are you sure that fuel is getting into the float bowel?

 

*is it in nuetral?

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There is a few things I would be checking. Check that you don't have an air leak between carby and engine. Check that there are no blockages in your exhaust. If the bike isn't revving freely in the lower gears but does in higher gears I wouldn't assume its a plug problem. Is your power valve opening when it should? Don't use the BR8ECM unless you are riding it like a race bike. Use the same plug as a 250 exc. I once had similar problems with a kx 125. Turned out to be a faulty pick up coil, not to be confused with ignition coil.

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Confirm the big three, Air, Fuel, Spark before you do anything else, they have to all be present at the same time for the bike to run, then check your reed block as well. Are the reed petals chipped, broken, or missing?

Edited by Rider 41
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I would say check your main coil wire, at both ends, the plug caps' end, first, then  the coil's end.

If the inner core looks suspect, clip 5mm wire off each end, spray some contact cleaner, tread the plug cap again, and most important, thread the wire into the coil receiver end, securely.

Make sure the wire's ends are bottomed out, the connections feeling solid. You should definetly feel some resistence to any spinning movement.

 

Today, I have chased a blubbering, plug fouling, overly rich top end condition all day long, on my 2006 EXC 250, which would not go away  with smaller main jets.

Checked the carburator float level, all vent hoses, then moved onto the reeds, air filter, ignition rotor, stator plate, black box, all of the wire connectors, kill button, top end compression,;everything I could think of, including the first suspect, the spark plug cap.

Found nothing wrong.

The problem disappeared only when swappin the entire coil assembly with another 2st. KTM,  Kokusan coil unit.

Turned out the main coil wire had sone oxydation in the recess areea, where it threads into the coil box.

It did not look it had been neglected, stretched or pulled out; also, the rubber seal was still in good contition; but that one connection was weak enough to mess up the spark, and it did in the upper rpm only.  Down low, the engine ran fine, started first kick all the time.

 

Very frustrating, I spent hours spinning wrenches for nothing.

 

I suggest you to start by checking the easy stuff first, then move to the more complicated, hard to reach things.

 

Alpinerider

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Confirm the big three, Air, Fuel, Spark before you do anything else, they have to all be present at the same time for the bike to run, then check your reed block as well. Are the reed petals chipped, broken, or missing?

 

x2. Is the fresh plug coming out wet after you kick the bejesus out of it? If so is it fuel or oil? If its oil, I think your tranny side crank seal could be busted. if its fuel, you can confirm its getting fuel.

 

A healthy spark is a thick blue spark, white spark will only ignite an extremely flooded engine.

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Hi Eddie, just curious why not use the BR8ECM plug?

There is a few things I would be checking. Check that you don't have an air leak between carby and engine. Check that there are no blockages in your exhaust. If the bike isn't revving freely in the lower gears but does in higher gears I wouldn't assume its a plug problem. Is your power valve opening when it should? Don't use the BR8ECM unless you are riding it like a race bike. Use the same plug as a 250 exc. I once had similar problems with a kx 125. Turned out to be a faulty pick up coil, not to be confused with ignition coil.

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