gbruno21

Member
Jun 12, 2010
24
1
I need some help guys. I am an amatuer mechanic at best and I can't get my '88 KDX 200 running right. The rotor magnets tore loose so I purchased and installed a new rotor. I also replaced the stator (from RickyStator.com) while I was at it. The stator is correctly lined up with the timing mark on the engine.

The engine runs fine at idle. When I turn the throttle the engine stalls out. Any help would be appreciated. :bang:
 

geoffro

Member
Nov 16, 2007
47
0
OK I am a qualified mechanic but difficult (as all ways), obviously to diagnose your patient over the phone....If it is idling thats a good sign for spark... My gut feel to check carb/feuling side.Opening throttle slowly/faster??... has bike been standing?
some more info on how you got to this situation can help.Was it running fine before magnets tore loose?
 

gbruno21

Member
Jun 12, 2010
24
1
Quick history. Engine locked up and I did not know why. Took it to a mechanic who proceded to take the ENTIRE engine apart. Why he didn't stop after he took the rotor off I will never know. He wanted $2200 to put it back together and I said no way. I put it back together myself by looking at manuals and youtube videos. Has not run properly since.
 

geoffro

Member
Nov 16, 2007
47
0
Oh my word!!....I'm sorry but due to your "mechanic" I'm a bit more lost than earlier.
ok... by rotor I take it you mean "magneto"(thats what we call it anyway),left side,going over coils? bit rusty on '88 model. Did you put the keyway in that holds rotor in place?(thin halfmoon piece of metal fitting in a slot on tapered shaft)
 

gbruno21

Member
Jun 12, 2010
24
1
yes. I fit the magneto over the keyway. I have removed the magneto recently to check everything including the timing mark on the stator plate.

Since it is running fine at idle I am assuming that the stator is working correctly. My understanding is that the 2 stator coils are for ignition and the headlight. Is that correct?

When I received the engine back from the mechanic in 100 pieces I had to fit all of the gears, crank shaft, kick start mechanism, etc. all back into the case and put the case back together. I did not replace the crank bearings, I know that I probably should have, but I did not. I used Yamabond liquid sealant on the two halves of the case and pressed them back together. I did heat up the case in the oven at approx 200 degrees as I saw in a youtube video. Everything seemed to go back together very well. I changed out the piston rings, again, everything seemed to fit well. I checked the piston cylinder for scoring and it looked remarkably good for a '88 bike. I cleaned the piston head etc. Again, everything looked good and went together well. Is it possible that there is an air leak around the case somewhere that is allowing too much air into the cylinder? Would that make it run at idle but stall out when the throttle is turned?

I recently switched out the carborator with another KDX carb that my buddy had. It performed the same way, ran well at idle but stalled when the throttle was turned.

Could it be that the new stator is not working properly?
 

geoffro

Member
Nov 16, 2007
47
0
Well you have done a great job to get to where you are from where you started! with little technical know-how, well done!
Yes "lighting" coil and "ignition" coil. If both carbs are doing same thing then very good chance it electrical.if the cases leaked a little it would run lean(air going in by casings).Lean mixture normally causes revs to run fairly higher than idle and they do not want to come down. Pop the bike over to my house and I can take a look.I'm in South africa....
 

geoffro

Member
Nov 16, 2007
47
0
After more thought... if the casings have got a bad leak it could cause alot of air to go in and stall the bike when revved. Also have you checked the reed petals? they can mess you around too.
 

EYY

Member
May 22, 2010
159
1
As geoffro said, The electrical side of things is probably the easiest place to start. You could try checking all electrical connections and making sure there are no shorts anywhere which could be taking power from the ignition circuit. Have you put a new plug in it since putting it back together?

Did you change the crank seals while it was apart?
Have you completely disassembled the carb and thoroughly cleaned everything and blown compressed air through all passageways?
 

geoffro

Member
Nov 16, 2007
47
0
seals

10 points to eyy for the crank seals idea!! I was talking to another bike mechanic friend about your problem and he mentioned crank seals! something I overlooked...I'm getting old!!...especially if they are very old and not sealing so well after being apart and now together again
 

gbruno21

Member
Jun 12, 2010
24
1
Good info guys. NO, I did not change the crank seals. I know now that I should have while I had the case apart but being an amatuer at this I did not know it was necessary. I am quite sure that the timing is correct. I have the repair manual for the bike and I followed their instructions for lining up the timing. There is a distinct mark on the stator plate and a corresponding mark on the case. They are line up perfectly now and still having the same problem.

No, I have not changed the spark plug because it was working well prior to the rotor problem. I can change it, that is easy enough so that we can rule that variable out.

Yes, I cleaned the carb thoroughly. I soaked it overnight in a carb cleaner solution (sold in a gallon paint can ... I think it is made by "Gunk" and it is called "Carb Medic"). I also use a fine bristle from a broom to probe out all of the small holes until I can clearly see through them. Since I tried my buddy's carb from a KDX 200 that is running perfectly, and it didn't change anything on mine, I think I can rule out the carb.

Is there a way to stop any air from entering the case without taking it apart? For example, what if I put a layer of duct tape around every seam on the case to temporarily seal it up and see if it fixes the problem. I could do the same thing with plumbers putty or something like that. I dread splitting the case again if I am not sure that is the problem.

Any thoughts?
 

EYY

Member
May 22, 2010
159
1
You can spray aerostart or similar products around the areas that you think might be leaking when the bike is idling. If the revs increase at all, you'll know you have an air leak
 
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