Need Help-Bike won't idle

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#1
I'v got a '93 KX250 That I cannot get to run right. I was hoping you guys could give some posible causes or troubleshooting tips before I decide to try a new carb...
The bike will not idle, I have to just bareley hold the throttle open to keep it running. It's REALLY rich on the bottom, but jetted lean(stock pilot is 50, tried 40 & 35 with no effect). I've cleaned the carb many times and checked the float height. The idle speed screw and the air screw seem to have no effect while trying to get it to idle. The bike runs decent past 1/8-1/4 trottle, but theres nothing down low (way too rich). I'm fairly certain the carburator is the source of the problem (it's got a fresh top end).
Is there something else which would cause these types of symptoms? Is it possible that the carb could just be "bad"? I just want to be certain what the problem is before I try a new carb.

Thanks
 

CC_RIDER

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#2
Hey E-DOGG, I too am needing some tuning advice, but I thought I might get into your problem and offer some help.

Let me start by asking some questions.

How long have you owned the bike?
Did this problem exist before the new top end job?
How are you determining that it is too rich on bottom?
When you are holding the throttle open to keep it running, is it idling at a normal speed?

One thing you might not have checked was the float needle.


You might try removing (temporarily) the air screw to see if that leans it up.
 

fremontguy

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#3
My experience jetting Ktm 300 has pointed me towards richer pilot, 42 and leaner straight diameter of needle for the best idle.
 
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#4
CC_RIDER- to answer you questions...

1) I bought the bike used almost two years ago, it needed a little work (just maintinence) but i got a good deal on it.

2) It's had this same problem ever since i have owned it (wont idle/too rich). I just replaced the top-end last week because it needed it, but it did not help the problem either.

3) I think it's too rich because of the exessive smoking and the fact that when I pull the plug, it's usualy wet. Not fouled, not oil.

4) When I hold the throttle open a bit, it will "idle" at a normal or constant RPM. but it's still really rich and smokes ALOT.


Hey fremontguy- Are you in frmont CA? Where do you usualy ride?
Im in Union City myself.

Thanks for the response guys!
 
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#5
I tried using the leanest pilot jet jet I could get ahold of (35), and this thing wont even come CLOSE to idleing!

Any ideas?
 

CC_RIDER

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#6
OK, I have no scientific proof for any of the following suggestions. :D

Would'nt a longer idle speed screw hold the throttle open enough that you would'nt have to hold it open by hand? Try removeing the spring so it can screw in farther.

Have you tried removing the air screw yet?

If that does'nt lean it out nothing will!

I'm not suggesting you ride it this way, it's just a test, like applying the choke when you're running too lean.

I mentioned before checking the float valve. Even if the float sets at the right angle, if the valve seeps you get a flooded condition.

Have you tried a NEW main and throttle needle? If these are worn from use and vibration, extra fuel could be getting sucked up into the mix.

And just for grins, have you tried a richer pilot? At this point what could it hurt.

Things are'nt always as they seem.
 
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fremontguy

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#7
Good info there in replies. E-dogg, I sent you a PM about riding.
 
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#8
I give up

Hey guys, Thanks for the suggestions, I really appreciate it.

Well... at this point im about ready to try a new carb!

After I let the bike completely warm up, (air filter removed) and held the thottle about 1/8 open to keep running (at a constant RPM)...

1) I screwed the idle speed screw althe way in, then almost all the way out.
This had NO EFFECT on the idle speed or the mixture. (still holding throttle at 1/8 open)

2) I completely removed the air screw all together, this had NO EFFECT on the mixture or idle speed! (still hoplding at 1/8 open) the RPM's didn't even change!?

3) I tried putting the richer pilot jet back in, but again this had no effect.

4) I have leaned all of the jets a few steps leaner, and moved the needle clip leaner (not a new needle though), and still NO EFFECT.

And just for grins :D I might try heavin the darn thing off a cliff! (That'l solve my problem)

Thanks again for the suggestions, they are much appreciated.

I think I might just try a new carb if i can find one cheap at a salvage yard,
unless anyone has any idea what would cause these symptoms besides the carb (am I overlooking something?)
 

CC_RIDER

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#9
E-DOGG, if you get a new carb, report back on this thread and let us know if that solves the problem. (I don't how it could'nt!)

Good luck!
 
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#10
New Carb!

Just wanted to let you guys know that the new carb did the trick! Now it runs like a new bike (or at least how it's supposed to run), Should be a great weekend to go riding:) Thanks again for the troubleshooting suggestions though, I just wanted to be sure that the carb was the problem before I replaced it.
 

CC_RIDER

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#11
Great!

It's always a relief to get the bike running right, especially when you have to replace parts that you are'nt sure need replacing. What a bummer it would have been if the new carb had not solved the problem!

So off you go! Have fun!