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mobrown · Feb 12, 2004

Helping my nephew with his KX125 ('91) that won't start. I checked the spark and it seems fine. He had left the gas on so I shut it off, pulled the plug, kicked it to get fuel out of chamber and reinstalled the plug. Still no start.

Took carb bowl out to check for dirt... had none. Put it back on and it still won't start. Comression seems to be good. Bike had new top end done. Guy he bought it from used 32:1 mixture for break in and it is jetted for 50:1. It smoked a lot when it did run but decreased once warm. Drained gas and put 50:1 synthetic in 2 weeks ago and it did smoke less but still significant so I changed the packing in silencer (old packing was very oily) hoping that a lot of smoke was from oil in there. Haven't been able to start it though so don't know if it helped. Plug seemed to have pretty good color... didn't foul after he rode it last weekend.

This bike used to start with one kick just a few days ago. What else should I check? Could his leaving the gas on for 5 or 6 days have dome somethig to carb?

Coolector · Feb 12, 2004

you have to eliminate if you already haven't is fire and fuel. Take the plug out and reinstall the wire and lean it against the cylinder and get your son to kick the bike, you should see a blue spark on the plug. If ok carry on to fuel. an easy way to tell is to clean the plug real good even use some heat and reinstall it turn on the gas and kick er a few times, remove the plug again and it should be wet. She should start if you have both of these unless the timing is way off or the kill switch is stuck on or something stupid. I would also take the carb apart if I were you and blow it clean, could be a peice of dirt stuck in the pilot jet, small one.
Good luck hope this helps.

mobrown · Feb 12, 2004

Thanks

It does have spark but I'm not sure if it's blue... looks more like white but there's kind of bright lighting where I am working on it so it may be blue. The plug does get wet when I put it back in and try to start it.

The kill switch was disconnected byt the previous owner (says he did it for racing?). If the kill were grounded would there still be a spark?

Would appreciate any any additional advice from anyone very much.

Coolector said:
you have to eliminate if you already haven't is fire and fuel. Take the plug out and reinstall the wire and lean it against the cylinder and get your son to kick the bike, you should see a blue spark on the plug. If ok carry on to fuel. an easy way to tell is to clean the plug real good even use some heat and reinstall it turn on the gas and kick er a few times, remove the plug again and it should be wet. She should start if you have both of these unless the timing is way off or the kill switch is stuck on or something stupid. I would also take the carb apart if I were you and blow it clean, could be a peice of dirt stuck in the pilot jet, small one.
Good luck hope this helps.

Jeff Gilbert · Feb 12, 2004

replace the plug anyway

WWR · Feb 13, 2004

Mixing less oil in your oil/fuel ratio actually makes the air/fuel ratio a tad richer. Sounds like the bike is too rich to begin with. Time to swap your jets in your carb, that is the only real fix (provided that your airfilter is clean and everything else is in good condition).

And throw a new plug in there. Those things can be real finicky.

joe28kdx · Feb 13, 2004

If he let the fuel on, the bottom of the engine could have a pile of fuel in it, you kick it over and poof the plug fouls.
Get a couple of NEW plugs, take the old one out, put it back on the wire and ground the tip against the head or something, (when you kick it over this prevents the CDI box from getting smoked).
Put you finger over the spark plug hole and have you son kick 'er over.
Feel compression???? Is you finger wet???? kick it over a pile of times, (your working the fuel out of the bottom).
I take a new plug, put it in the oven to warm it up, then install it.
No choke, full throttle, kick your brains out until it starts, (Keep thinking, that Gaod it's not a KX 500!). After a while you may want to try firing it with the choke on the normal way you start it.
If it doesn't fire, I'd look at the reeds, they may be chipped, (not letting the engine seal on compression).
I bet it loaded up really bad. MY ATK will do that at times, it get ignorant!
Once you get it fired, THEN rejet it, (if it ran before it SHOULD fire).
Run a compression check on it after you get it fired.
I preach to my sons, turn the fuel off!
My one son forgot to remove a rag in the air boot, (we put one in there to keep, "stuff" out when we remove the airfilter). His bike fired for a second, he spent 3 days sweating trying to fire it. Didn't want my help, cuz he kenw all! I noticed it cuz the slide didn't make that, "clicking noise" on the idle screw.
Good luck!
Joe

FLBob · Feb 13, 2004

If it was running OK and now it doesn't (and it has spark) it probably has lots of gas/oil in the crankcase. Shut the gas off. Hold throttle wide open and kick till you're beat. Pull the plug and kick some more with the throttle wide open. Put a good plug back in-one you know is good, cause you saw spark when you tried it. Leave the gas off and throttle closed and kick a few times-if it doesn't start, pull the plug and look to see if it's wet. If wet, it probably means the gas valve on the tank is leaking by and the neeedle valve is letting too much gas into the carb. Drain the carb and repeat the above kicking again. You need the plug to come out dry to make sure you've got the crankcase cleaned out.

Turn the gas back on. Try to start without the choke. If no start, then try your normal procedure, with ckoke, etc. If still no start, pull the plug again-should be wet by now-if not all the above was a waste of time except now you know it's not flooded and probably not getting any gas!

mobrown · Feb 14, 2004

Greatly appreciated...

Dudes thanks for all of the advice... I took it and got it running!! I do think it needs jetted though because it runs kind of boggy until you hit the high revs. I remember reading in one of the forums that different jets are utilized depending on the position of the throttle is that correct? If that's so how could I get it to run a little leaner at low to mid throttle? It seems like it's getting too much fuel down low... lots of excess exhaust down low also.

Any recommendations or advice?

Mavic · Feb 14, 2004

mobrown said:
It seems like it's getting too much fuel down low... lots of excess exhaust down low also.

From what I have heard, bogging is usually a symptom of being too lean. I could be wrong though. I would adjust the needle jet clip position for 1/8 throttle to 3/4 as that is it's approximate region of influence. 125's are not really noted for their overwhelming lowend so that may be just a factor. I haven't been on a 125 in a long time so take this with a gain of salt.

If it is soft from idle up, you might be too lean on the pilot aka slow jet. You could check your air screw and see if it is 1.5 turns out from closed. The more turns out the leaner, the more turns in the richer. On a similar note.... Some have suggested that you set the bike to idle the bike around 1200rpm and adjust the air screw in 1/4 turn increments to achieve the highest possible rpm at that setting. Shut the bike down and count the turns to full closed. If it is greater than 1.5 you can go down one jet size on the pilot. Less than 1.5 turns up one size on the jet.

Hope this helps.

mobrown · Feb 14, 2004

That was quick!

Thanks for the quick responce Mavic... very detailed and informative. I'm gonna give it a try.

You ride an '87 CR500? That thing must be a monster! How do you keep that front wheel on the ground? :ohmy:

Mavic · Feb 14, 2004

Good throttle discipline and putting my 200lbs as close to the front as possible when the right hand feels the need. Usually that still brings the front up but it is very controllable from that position. It those times when the seat gets a little slippery that things get pretty crazy. It tries it's best to shoot me off the back. Hasn't happened yet but I know that day will come soon enough. Still loads of fun!!!!

Mavic · Feb 14, 2004

Mo,
Checking the post again, you stated excess smoke and that is sometimes a symptom of being too rich. However, you should really follow these guidelines.

Warm the bike up by blipping the throttle until the cylinder and/or radiator are emitting nice warm signs.

Take the bike and run it though the gears all the way to WOT. These babies like to be run and once the bike is good and cleaned out, you will better be able to assess your seat of the pants jetting diagnosis on the low end. After you enter a slow speed section from the higher rpms, see how the bike responds. It if boggs, sort of like bwaaahhhaaAAAAA, it is probably lean. If it blubbers/4 cycles and blows lots of smoke it is probably rich. Seat of the pants diagnosis probably is not the best method but is generally close.

BlazinBoy · Feb 14, 2004

Careful application of throttle!!! lol

mobrown · Feb 16, 2004

Confused...

Had the bike out Sunday and warmed it up. Really boggy while warming up and a lot of smoke. I took it out and opened it up and it ran really well. Seems like once I do that it runs great.

I still want it to run better though. Yes it perks up and runs strong after blowing it oput but what do you think is the cause of the xcess smoke and bogginess before it get opened up? Jetting? If so which way do you go? Does excess amoke mean too rich or what?

Would appreciate any and all advice. Thanx.

Mavic said:
Mo,
Checking the post again, you stated excess smoke and that is sometimes a symptom of being too rich. However, you should really follow these guidelines.

Warm the bike up by blipping the throttle until the cylinder and/or radiator are emitting nice warm signs.

Take the bike and run it though the gears all the way to WOT. These babies like to be run and once the bike is good and cleaned out, you will better be able to assess your seat of the pants jetting diagnosis on the low end. After you enter a slow speed section from the higher rpms, see how the bike responds. It if boggs, sort of like bwaaahhhaaAAAAA, it is probably lean. If it blubbers/4 cycles and blows lots of smoke it is probably rich. Seat of the pants diagnosis probably is not the best method but is generally close.

joe28kdx · Feb 17, 2004

Pilot/ air screw takes care of idle to 1/4 throttle, slide/needle take care of 1/4 to 3/4 throttle, main takes care of WOT.
Some overlap, best advice,
look @ in this form and others to set the jetting, or how to do it---- remember, temp make a HUGE difference along with fuel age/type, oil mix.
if you never did one work with someone who has or send the $$ at a dealer and have him set it up, then you can write down what he did and play from there!
Good luck,
Joe

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