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Why does my dirt bike keep fouling plugs

I have been fouling plugs every since I purchased bike. I have to put in a new plug evrytime i go riding. I do some soft riding with the kids and some hard riding as well. I have tried a hotter plug and it helps a bit, but still fouling about every 3rd ride. I even took it to yamaha and all they said was to put a hotter plug in. Did I buy a defective bike? What can I do to solve this problem? There's nothing worse than having to push your bike back to the truck.....

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  • Motorcycles Master
  • 40,748 Answers

Hi, Joey assuming it's a 2 stroke the usual suspects are:
1. The first thing to do if your spark plug has been fouled is to check the air filter. If it's really dirty, that makes it difficult for air to get through to the engine, causing a rich condition. Either clean it thoroughly with some Air Filter Cleaner or buy a new filter. Before you put it back in the air-box, treat with a fine mist of some air filter oil or spray. "WARNING" adding too much oil can also clog up the filter, resulting in another fouled plug.
2. While the gas/oil ratio doesn't equate to what the jetting is, you can still foul plugs, or worse, if the mixture is wrong. Depending on your bike, it's best to look at your owner's manual for the correct ratio. For most 2-stroke motocross bikes, a ratio is 32:1 or 40:1, the gas being 32 or 40, and oil being 1. For those that don't it, it means that for every 128 ounces (one gallon) of gas, you add 4 ounces of 2-stroke oil for a 32:1 ration, or just over 3 ounces for a 40:1 ratio.
If you have too much oil in the mixture (such as 12:1), then you will probably end up fouling the plug because it is more difficult to burn that much oil. Don't try to cut corners with the oil though, because it's very important for your dirt bike's engine. 2-stokes need the oil for lubrication on the cylinder walls, so if you don't have enough (or any for that matter) then the cylinder walls will run dry, causing it to overheat and seize the engine very quickly. So it's very important that you put in the right mixture pre-mix to your 2-stroke gas tank.
Also, 2-strokes have reeds that air and fuel go through into the cylinder, so if they are cracked or broken the bike will not run right. This could cause the plug to foul, so before you go out and buy anything expensive, make sure the reeds are in good condition.
3. While this usually isn't the main problem, it could be that your spark plug isn't burning hot enough. Having a hotter spark will ignite the fuel stronger, leaving less residual gas/oil in the cylinder that could cause the plug to foul. This "ISN'T" the best choice, but I'd say it's safe to go one plug hotter than stock. Keep an eye on the plug color you're looking for a light tan color anything whiter and you could burn a hole in your piston. Spark plug manufacturers aren't always the same, so make sure you find out how they rate them.
4. Almost every motocross bike comes rich from the factory (especially Honda 2-Strokes when they were being made). It's usually a pretty simple fix, but many riders are too lazy and would rather continue buying plugs instead of spending a few bucks on jets.
5. Piston rings badly worn or broken.
6. Faulty ignition coil low output.
For more information about your question and valuable "FREE" downloads that you will need please click on the blue links below. Good luck and have a wonderful day.
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Posted on Jun 06, 2017

6 Suggested Answers

6ya6ya
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Posted on Jan 02, 2017

Benimur
  • 6966 Answers

SOURCE: new spark plugs last 10-15 minutes of riding

Hi and welcome to FixYa,

Offhand, the only factor to be checked that could foul a sparkplug for your bike would be the 2T oil injector/pump. There is too much 2T oil going to the combustion chamber. Either the injector would require restricting or for some reason, there is also 2T oil in the fuel tank (pre-mix).

Good luck and Thank you for using FixYa. Happy Holidays.

Posted on Dec 07, 2008

rselvy
  • 83 Answers

SOURCE: kawasaki kx 250 fouls spark plug in 30 minutes

You definitely need to change the oil mixture to at least 40:1, use a good grade of 2 stroke oil. You do NOT need to return the bike. I'd highly recommend using an NGK B7EV spark plug. A hotter plug will stop the premature fouling. I would not recommend you decrease the oil to 50:1 because you are essentially robbing the engine from adequate oiling for the piston, KIPPS valves and the bearings. The hotter plug will make a huge difference but remember if he gets to the point where he is able to ride the bike to it's potential he will need to run the cooler plug, B8EV or B9EV. You can also use a cheaper plug in the same heat range, B7ES or B8ES. Those plugs should cost about $1.25 ea. and are an affordable cost of running the bike. It's not uncommon to replace a spark plug frequently, it's the nature of the 2 stroke engine.

Posted on Dec 08, 2008

  • 3567 Answers

SOURCE: bike bogged down like plug fouled now wont start

Based on the information given, I think you may have a hole in the top of the piston. It sounds like pre-ignition, ( AKA detonation and engine knock ). Pull the cylinder head and check the piston and cylinder head. Sometimes the top outer edge of the piston disintegrates due to the heat. Replace the piston and rings and remove the carbon from the head. Be sure you run 32/1 mix on gas and oil. That's 4oz two stroke oil per gallon of gas. Only use premium gas.

Remove and clean the carb. Be sure the carb mount bolts and carb manifold bolts are tight. An air leak will cause the engine to run hot.

Please rate this solution. Thanks

Posted on Apr 07, 2009

  • 11 Answers

SOURCE: Bike is sputtering in high 2nd/3rd gear, best kind in idle

Sounds like a lean condition. Spark plug should be a tan brown.
I would say the carb probably wasn't drained prior to storage and your main jet is gummed up. Gas deteriorates very quickly especially in vented containers like the float bowl of a carb.
clean your carb for sure.

Posted on May 20, 2009

susho
  • 18 Answers

SOURCE: Problems starting my 2003 Yamaha TTR225

The cylinder is the coil. It might be bad but it is expensive and you would not replace it till you know for sure there is no spark. You can take the plug out and then put it on the wire and ground it against the engine while a friend cranks the starter. Look for the spark flash. Make sure the kill switch is in the "on" position.
If that shows a spark then you will need to move into a different line of troubleshooting. I always recommend that people buy a Clymer manual.

Posted on Jul 31, 2009

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2nd check air screw settings are 1-5/8 turns out
3rd check that main jets are 105s

Hope this helps(if so please mark as very useful)
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