99 yz250 weird fouling plug problem???

[minitrucker83]

I know this has probably been beat to death on here but this seems odd to me. Im new to bikes and 2strokes so this might be my problem completely considering the previous owner praised the bike for not fouling plugs. I ride at st joe state park in Missouri. Sandy flats w/ some trails, and rolling woods with trails. Im a newbie to riding so im not pushing the bike 100% or very often. I can unload my bike and go out riding for a couple hours in mixed terrain at varying speeds from putting around to wrapping out the gears in the sand flats. Ill even kill it a few times(from my inexperience) in the trails or sand. Bike will start right up and run fine if I kill it while riding. When I go back to my truck for a break its about 200 yards of slow speed riding thru traffic to get back. Sit around for a half hour or so and hop back on the bike. The bike will usually fire up with no choke, within a kick or two but it will die before I get back out in the riding area. Plug is fouled everytime. Ive only got about 7-8hrs of seat time and ive fouled 3-4 plugs the exact same way.

Bike info: 99 yz250 fmf pipe & silencer, boyesen power reeds, clean air filter, 32:1 yamalube previous owner ran it figured I'd stick with it, NGK bre8eg(stock plug).

Bike seems to run real strong down low and up high. Might have a lil low end stumble when you first roll into it??? Walks away from my roomates 01 Kx250 though anywhere in the rpm's. Also smokes a decent amount, pretty white too. Im not sure what or if anything has been done to the carb. I was thinking I should check the float, then check the pilot air screw setting, and then try moving the position of the clip on the jet needle.

Does this sound about right for a plan of attack? I have a yamaha service manual to refer to for stock settings.


TIA,
Dustin

[fastman69]

If it is smoking something is wrong. clean out the carb and check your jetting. You could run a hotter plug (change the 8 to a 9, i think that is right) and you can also lean the premix a little.
Another thing, do you turn off the gas when you sit around?

[dajogejr]

Originally Posted by fastman69

If it is smoking something is wrong. clean out the carb and check your jetting. You could run a hotter plug (change the 8 to a 9, i think that is right) and you can also lean the premix a little.
Another thing, do you turn off the gas when you sit around?

Without trying to sound like a total jerk....please don't take this advice.
Here's why....

A two stroke can smoke, it all depends on what kind of oil you use. Synthetics tend to smoke less, castor or man made oils tend to smoke more.
Cleaning the carb is good advice.

In NGK land, the higher the number, the colder the plug...opposite of everyone else. You do not change plug heat ranges or put less oil or more oil in the mixture to fix a mechanical problem or a jetting issue.

You have two potential problems.

1. Top end is worn
2. Jetting is incorrect.

Since this bike is new to you...are you riding at the same altitude, humidity and temps as the previous owner.

I think the jetting is off....personally...
First dial in the main, this link holds true for any two stroke on gas.
2-Stroke Plug Chop How-to

Then work on the needle, then the pilot jet/air screw.

The needle controls 1/8 throttle to almost 3/4 throttle. If it feels boggy, that means it's rich. if it feels zingy...or it revs but no power, it's lean.

I think you're rich...because of fouling the plugs. But it could be a worn top end, it could even be a bad crank seal on the PTO side allowing tranny fluid to mix in the combustion chamber causing it to foul plugs.

[JordanM]

Also sounds to me like you arent revving it high enough, when I first got my bike I rode it like a 4 poke and kept the rpm real low. Doing that doesnt let all the gas burn so it fouls. Try getting a new sparkplug, and ride with more rpm.

[dajogejr]

A properly jetted bike shouldn't foul plugs..period.
If your bike is fouling plugs, lean out the circuit that is too rich causing the plugs to foul.


That's like saying your dad's old carbureted car would foul plugs if he drove it around the neighborhood...he had to drive it on the freeway or it's foul them.

This is not a two stroke/four stroke thing either...it's a matter of correct mixture at all engine loads and temps...so please don't say something about the oil in the gas.

Traditional carbs have 3 jetting circuits.
Pilot jet/air screw, needle and Main jet. All can be adjusted either by new/different size jets or adjusting the height (needle).

[ROACHIE]

please dont refer to stock settings if you have aftermarket parts cause it wont work...also try running a br8es or b8es and run premium gas if you are running cheap regular gas you are gonna foul plugs the octane rating does make a difference in power reliability and cleaner top ends...also oil makes somewhat of a difference...i say try 92-94 octane rating pump gas mixed at 40:1 or 32:1 with either klotz r-50 or motul they are full synthetic oils and run a b8es or br832 plug with that and see where that gets you

[minitrucker83]

Thanks for the replies. As far as elevation, temp, and humidity they should be the same as the previous owner. We live within 20mins of each other and frequent the same riding area. Ill do a compression test next time Im out. It runs strong and starts easy with a fresh plug so I would like to think the engine is in decent shape.

[minitrucker83]

Originally Posted by ROACHIE

please dont refer to stock settings if you have aftermarket parts cause it wont work...also try running a br8es or b8es and run premium gas if you are running cheap regular gas you are gonna foul plugs the octane rating does make a difference in power reliability and cleaner top ends...also oil makes somewhat of a difference...i say try 92-94 octane rating pump gas mixed at 40:1 or 32:1 with either klotz r-50 or motul they are full synthetic oils and run a b8es or br832 plug with that and see where that gets you

I wouldnt rely on stock specs, just for reference to see if the carb has even been touched. I read on here before about people having problems with the plug my bike uses. I also use premium fuel which is usually 93 in my area. I thought about changing premix oils and ratios before I ever rode the bike. Some praise yamalube others hate it. I bought some castor 927 but decided to run what was left of the yamalube before I changed. Now that im having a problem fouling plugs Id rather not throw another variable in there to mess with me figuring out the current problem.

Thanks again.

[dajogejr]

I'd steer clear of the castor for your particular bike. It works GREAT for methanol bikes, but I'd run Klotz R50 or Supertechniplate for a gas bike.

As said, 32:1 or 40:1 are sufficient ratios.

[dan151]

yeah im having the same problem with my 99' yz250, kinda ironic haha, i ride for about two hours then the plug goes. ive gone threw 3 plugs. i drained the gas thinking mabe the fuel mix was to rich and mixed at 40:1 with yamalube 2r and it runs fine with the chock up then with the choke down it bogs and then dies then wont start cuz the plug fouls.

it ran perfect when it was 50 degrees but now its 80 and it fouls like crazy.

ive got a pro circuit pipe with fmf silencer and the guy before me said it was jetted fine. should i try going a little leaner on the main? or move the needle clip to lean it out a little more?