[KX 125] SEVERE Bog

[RyClef331]

I just picked this bike up with a fresh rebuild on the topend. The price was WAY too good to pass up so I snagged it. NOw here's the dilema. TO me being a car guy and not knowing anything about 2 strokes other than the basics....it sounds like its hitting a "rev limiter" You crack the throttle and it makes a (go ahead and laugh) " brrRAP-BUUuuuuh-BUUuuuh-BUUuuu." sound. ALL i can get from anyone is "Check the plug." Its obviously not reving and its getting a WHOLE lot of fuel so the plug is getting soaked. I don't know if this is an ignition problem (we've tried two different coils and multiple plugs) or fuel tuning. Pretend I really dumb as I don't know a thing about tuning/jetting these bikes. I'm a car guy and pretty mechanically inclined. I just wanna ask the experts before I go out and make a costly mistake. Thanks for the help

 

[jackdrinker]

take the float bowl off, my rm250 started to do this and the float was clogged.. fuel was running out of the tube..

 

[cactusreid]

Ryclef : You most likely have a carb problem of some kind. Did you change altitude (of the bike's home area} to where you live? You may have to change some or all of the jets in the carb if you made a significant altitude change from where the bike came from.Check with the locals for jetting specs for your area if this is the case. ( 2-3000 ft will make a huge difference on some bikes as to how they run) It may be just a plugged up jet/old gas in the float bowl of the carb. Is the air filter cleaned and reoiled? CLean the engine first and then proceed to next step. Pull the carb off the bike, un screw the carb cap and pull out the slide and then take the float bowl off,check for sludge in the bottom of the bowl and then clean out the jets. Use a can of sprayable carb cleaner, unscrew the main jet( hex one on the post in the middle) next take out the pilot jet (small flat blade down a tube close to the main, and spray it clean all over those little holes. now slide the pin out of the float tab and remove the needle valve and clean this stuff as well. Write down the #s that are on the jets for reference later. put it all back together ( no parts left over this time-ok? ) I'm a bodyman so I know this joke!! check and clean everything else on the carb with the spray. Check the small flatblade screw (airscrew) at the back on the side. most bikes will run pretty good with about 2.0-3 turns out from bottomed in GENTLY to the carb.Now pull the spring up to the cap with a couple of fingers to release the funny looking plate on top of the needle in the carb slider. release the cable out of the notch and seperate the slider from the cable. some carbs have a screw or 2 or a hex nut and a plate holding the needle in place. Pop the needle up and see which slot the clip is in #1 is at the top #5 is at the bottom- write this down there will be a test later!! now put it all back together and try it out to see if you solved or at least helped out the problems. I bet you will notice a big improvement. Be careful to get the carb back in the rubber boots with a good seal ALL the way around and the clamps snugged up when you reinstall the carb.Now if REPUTABLE locals gave you #s of jets that were different that yours,proceed slowly changeing one jet at a time and then testing the result. this way you will beable to see /feel the result/good or bad. You will also get good at RE &RE of your carb. Good luck I'll keep a eye on this thread for your comments.

 

[RyClef331]

Cactursreid...you gave me exactly what I've been looking for. Thanks ALOT. I'll be trying all this tommorow hopefully. A friend of mine I work with is a sponsored local racer and he said he'd gimme a hand with this. Are jets interchanngable bike to bike (different makes and models)? Also, can anyone give me a link to an exploded view of a carb so I can be sure of what I'm tinkering with.

 

[cactusreid]

Ryclef: Jets are specific to the type of carb(mikuni or Kehein) and a bit by yr of the bike. Get the same shape/size as what you take out or want to change and you will be okay. The # of the jet (370-or 380 or 390 is the difference in the amount of fuel that the jet will let through. Bigger# Is More-pretty simple EH? When you take the carb apart,go slow,and lay everything out on clean paper towels so you don't forget any pieces when you reassemble it.If the bike hasn't changed altitudes by a lot just clean every thing and try that. Do a bit of research about jetting on this site,I think Eric Gorr has some very good articules on how 2 stroke carbs work.

 

[RyClef331]

We're at sealevel pretty much. Carolina Coast. The bike has been here for years so I'm pretty positve they didn't mess with the jetting b/c of that. I'm going to start the carb tear down right now. Thanks again.

 

[cactusreid]

Go slow and don't let any dirt down into the engine-stuff the hose with paper towel. Good luck'I'll check back soon.

 

[RyClef331]

The clip on the main needle is at the top (#1). THe air screw WAS a half turn out. I set it at 2 to start with. How do the clip setting on the main needle affect the A/F Mix? Whats leaner or richer?

 

[cactusreid]

Ryclef- We are in to the tecnical stuff now. Pilot jet controlls 0-1/8 throttle(as you twist) airscrew helps to fine tune this portion. the needle clip position #1-5 controls 1/8-to about 3/4 throttle openings.The higher the clip position (#1 is the top remember the test part?) the farther down into the main jet the needle drops and the more the main is "plugged" so less gas flow with the same amount of air =leaner mixture. If you drop the clip tp #3 you will raise the needle in the main jet allowing more fuel through the main jet. This will make the mixture richer in the midrange part of the throttle openings. Your engine "doesn't KNOW" what main jet is there until you pull the needle all of the way up and out of the main jet. If your needle is in #1 (top) slot you can safely drop your pilot by 1 size. #40 down to a #35 for example. when you do this also move the clip to #3 on the needle and you will have some fine tuneing adjustment with just your clip position on your needle. See It's not hard at all is it? Clean the carb and the jets first as that may be more of a problem that poor jetting. The bike probably ran good on this como of jets before you got it. Alot of people think that they need to change the main jet when actually most of your riding is done in the lower half of your throttle openings. start there first.

 

[RyClef331]

Ok well, the main jet was #162 (Keihn Carb btw). I took the main needle out and and check everything and cleaned it all. I'm going to crash and try to get up a decent hour and check out the progress tommorow. Someone else mentioned to me in an IM to check the powervalve (located on the front of the head above the pipe).

[edit] I'm gonna be up for a bit surfing around so if you reply tonight, awesome. If you have AIM you can get me at RyClef976

 

[cactusreid]

Ryclef: Don't forget to take the pilot jet out (the little one that's down the tube with the flatblade end in it) and clean out the small holes with the spray cleaner. also record the #s that are up on the side of this jet. This is the jet that you could go down a size on. If you do don't forget to raise your needle to #3 slot. This will effectively put you right back in the same jetting range,except you will now have some adjustment (needle adjustment up or down) to help fine tune your low and midrange fuel/air mixture.Start shooting questions if I'm losing you!

 

[RyClef331]

its a #42 on the pilot jet, 162 on the main w/ the needle on the #1 position. Air screw about 2 turns out. I"m going to go try her out. I'll let you know

 

[RyClef331]

2 days and i'm already starting to dislike this thing...

 

[cactusreid]

WAS-UP? No changes from before you cleaned the carb?

 

[cactusreid]

I just went back to your first post that said a fresh rebuild. See if you can find out who did it and ask them to help you? Unless it was the guy you bought it from. Then maybe it explains why the bike was for sale. What color is your plug? Is it the right plug for the bike? Is it wet or dry? Oil fouled,or gas fouled? what mixture of gas /oil are you useing?

 

[RyClef331]

It was rebuilt by a shop here in jacksonville and they want a substantial amount of money just to get it in and look at it. I'm more than confident I can get it running but it just like any problem...the troubleshoot is the most frustrating part. The plug is soaked whenever I take it out...right now it won't even start even when i clean the plug off and put it back in there dry. Its pretty black and sooty so I'm assuming thats oil fouled. The gas mix is 32:1 with 93 octane. The plug is a BR9ES which is what has been ran in it for years (not the same plug...same part number). I check the power valve to fun and alot of black oil came out of the pipe when I took it off...I don't know if anyone this helps at all but I really do appreciate your help.

 

[cactusreid]

Ryclef: see if you can find out and compare what jets the bike called for from kawi. Keep in mind the factories always jet there bikes on the rich side. this prevents people from blowing up new bikes with lean jetting specs.

 

[slodsm]

cactus, just want to tell you that it's pretty awesome you are helping him out like this. I am his room mate but almost as lost as he is on 2 smokes and we work opposite shift. Two of our buddies have raced for years and one was carried by Honda of troy and the other is now carried by Yamaha of Troy but as we all have full time jobs it's hard to all get on the same schedule to get this thing fixed. I appreciate all the help you are giving Ry.

 

[cactusreid]

No problem! I just hope we can solve it. besides if I'm ever down in your area I'm sure I could hook up for a ride with you guy's.

 

[slodsm]

Absolutely man, we have 1 motocross and 3 supercross tracks within 1 hour, 3 within 10 minutes.

 

[cactusreid]

BUT BUT BUT------ I'm old and not very good at jumping!!!! But if you've got a good gnarly,twisty, log infested tight tuff trail -I'm there like a dog on a porkchop!!

 

[RyClef331]

That'd be around my home town... Durham, NC. Put it this way...52 miles of riding in two days...4-5 hours each day. Never rode the same trail twice...now if I can just get this pig to run. Tommorow my buddy is bringing his expertise and jet kit by to help me out with the tune.

 

[cactusreid]

Ryclef: You may want to look a little further-possibly a woodruff key on the flywheel may have sheared? does it ever backfire ? I'm just very suspicious that a bike that has been in the same area for years-all of a sudden it wont run on the jetting that's been in it all along. But from what you have told us so far-I'd put my bet on jetting being to rich al over. VERY STRANGE?

 

[RyClef331]

Yeah, I know. Bikebandit.com has a good micro-fiche exploded view break down of the parts. That helped me out LOADS on identifying all the carb stuff. If the jetting fiasco doesn't work out this week, I'm going to dig into the motor this weekend. One more thing...if I'm getting this all right, there is no way to lean out the mix of the bike short of re-jetting...correct?

 

[Caper007]

Hey great reading, I learned some stuff there. My yz was doing the same thing and my problem turned out to be the reeds not sitting flat on the reed cage. I just flipped the reeds over and everything was fine again