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95 yz250 plug killer

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I just recently rebuilt my bottom end on my bike and threw the old piston and rings back in. There's a one ring piston in it. It also seemed like someone tryed to port the bike also but didn't do enough damage to were I need a new cylinder. Every half a tank the bike fouls a plug. Ive tried different types of plugs ones that have a higher heat rating and still no luck. It seems that oil is getting passed the rings and coming out my tail pipe also. I've changed the jets multiple times but still no luck. Its just killing the plugs and they have no spark after I clean them. If anyone could tell me what i should do next that would be great!

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Time for a pressure test. Could be from the ring, but more likely trans oil is leaking past a main seal and causing it to burn a lot of oil and foul the plugs

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I just recently rebuilt my bottom end on my bike and threw the old piston and rings back in. There's a one ring piston in it. It also seemed like someone tryed to port the bike also but didn't do enough damage to were I need a new cylinder. Every half a tank the bike fouls a plug. Ive tried different types of plugs ones that have a higher heat rating and still no luck. It seems that oil is getting passed the rings and coming out my tail pipe also. I've changed the jets multiple times but still no luck. Its just killing the plugs and they have no spark after I clean them. If anyone could tell me what i should do next that would be great!

 

Ohm check your kill switch and ignition coil.

 

Was happening to me (fouling plugs every 30 mins). Replace both parts for $35 and haven't had the problem since

I have a 94 YZ250

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Ive pressure tested the the bike already and it sits around 125 psi. The stator coil was replaced but not the kill switch. And the crank seals and bearings were replaced also. How can I tell if the seals are leaking?

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Ive pressure tested the the bike already and it sits around 125 psi. The stator coil was replaced but not the kill switch. And the crank seals and bearings were replaced also. How can I tell if the seals are leaking?

 

Pressure test, 2-stroke leak test not a compression test.

 

125 psi is low.

 

There are 6 main components to the electrical system: flywheel, stator, CDI box, kill switch, ignition coil and spark plug.

 

My guess is if you swap in a good ignition coil and/or kill switch the problem will be fixed.

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125 is really low, was this warm with the throttle opened?

Should be closer to 200 (175-210 is good)

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It says on the manual. Good is 100-125 psi. I just redid the compression test. And came out with 125 +. And no throttle open and cold. Im working on doing the pressure test. But I also tried tightening the cylinder head bolts and the cylinder and they all turned just a little bit more so maybe it was not sealed all the way.

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It says on the manual. Good is 100-125 psi. I just redid the compression test. And came out with 125 +. And no throttle open and cold. Im working on doing the pressure test. But I also tried tightening the cylinder head bolts and the cylinder and they all turned just a little bit more so maybe it was not sealed all the way.

You can't just turn the cylinder head bolts. They need to be torqued to a certain spec. Your going to be having multiple issues soon if you keep mechanic'ing like this.

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I will 're loosen them and 're torque them. I jist saw some spots of oil coming out form the top of the head threw the gasket so I just decided to tighten them a little but more. They only turned like 1/4. Since my compression is low does that mean that oil is passing the ring and is fouling the plug?

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I will 're loosen them and 're torque them. I jist saw some spots of oil coming out form the top of the head threw the gasket so I just decided to tighten them a little but more. They only turned like 1/4. Since my compression is low does that mean that oil is passing the ring and is fouling the plug?

 

No, it's a 2 stroke. No oil sump

 

My guess is if you swap in a good ignition coil and/or kill switch the problem will be fixed.

 

My money is still on this..

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How much you bet? Lol cause it was the needle. It needed to be adjusted, moved it down and it is now on the fourth clip. Let to much in and drowning the cylinder

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How much you bet? Lol cause it was the needle. It needed to be adjusted, moved it down and it is now on the fourth clip. Let to much in and drowning the cylinder

 

So moving the clip on the carb needle fixed your "fouling spark plug to death after 1/2 tank" problem?

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Yep, saving gas too! Whoever adjusted that ou3 it all the way up so more gas was flowing in then needed.

Haven't fouled a plug. Been riding it for two days straight no problems so far

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How much you bet? Lol cause it was the needle. It needed to be adjusted, moved it down and it is now on the fourth clip. Let to much in and drowning the cylinder

Good find, man. 5th clip position is extremely rich. Stock is 3rd, I believe. 4th is usually pretty rich as well, but not unheard of.

 

You may have other problems, but that was a good find.

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Well ran into a problem today. Fouled a plug after two days. Bike started then bogged right before I was gonna leave. I have the clip on the fourth notch, two from the top. If I put it to three, that means id be letting more gas into the cylinder. The bike has the stock jetting in it. I ran it 40:1 with the clip on 4 and the stock jetting. Idk whats going on now. It also seems when the bike is idling its to lean cause it pops. Ill have to mess with it some more. Carbs are pretty tricky!

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