1982 KDX250 Will not start

[brawlingkhan]

Hello, I am new to the forum and fairly new to working on two stroke engines. Just purchased a 1982KDX250 last week and I cannot get the bike to start. Put a new NGKB8ES plug in and I have a fat blue spark when I ground the plug against the engine and kick it over. The piston and rings look to be in great condition and the bike has 155psi compression when I tested it after cleaning the carbon out of the exhaust port and top end of the motor. I tried putting gas in the spark plug hole and starting and I could not get the bike to start. I have a timing light and when hooked up the plug appears to be sparking under compression. The carb has been ultrasonically cleaned and is completely free of any debris or tarnish. The air/fuel screw is at 1.5 turns out and I did not alter the float level, however, I believe it is off and the engine is flooding because the plug is wet when I kick it over. Does anyone know the correct float height for this model or any advice on getting this running?

[6 Riders]

Air, fuel, spark... to much/too little of the first two will cause problems. I'd personally replace the pilot jet and not rely on it cleaning out. They are cheap. Since you dumped gas into the cylinder (don't do that) you'll need to "dry it out" and replace the plug. Also, take a very close look at the reeds. If there is ANY sign of distortion/cracks etc, they will need to be replaced.

In summary, check;
The carb is getting fuel, properly mounted, no air leaks in the boots (it easy to not seat the boot). The air filter is in place and clean take it off and look for rats nests). Reeds are in good shape, not bent, chipped, cracked, loose or too stiff.

[ohgood]

Hello, I am new to the forum and fairly new to working on two stroke engines. Just purchased a 1982KDX250 last week and I cannot get the bike to start. Put a new NGKB8ES plug in and I have a fat blue spark when I ground the plug against the engine and kick it over. The piston and rings look to be in great condition and the bike has 155psi compression when I tested it after cleaning the carbon out of the exhaust port and top end of the motor. I tried putting gas in the spark plug hole and starting and I could not get the bike to start. I have a timing light and when hooked up the plug appears to be sparking under compression. The carb has been ultrasonically cleaned and is completely free of any debris or tarnish. The air/fuel screw is at 1.5 turns out and I did not alter the float level, however, I believe it is off and the engine is flooding because the plug is wet when I kick it over. Does anyone know the correct float height for this model or any advice on getting this running?

17mm from the base of the carb body to the top of the float... and it should just be touching the "button" on the float needle valve body.


or, just eyeball it and make sure the float's center line is perfectly parallel to the carb body. you can check float height by putting a clear flexible tube on the carb drain spigot, opening the screw to that spigot, and putting the clear tube next to the carb body.

the bike should start even if it's rich from float height. make sure the tail pipe is blowing freely, and not clogged at all, anywhere from the head junction to the exhaust tip. it takes very little back pressure to prevent a two stroke starting.

[brawlingkhan]

Thank you for the advice. Turns out it was flooded badly so I took the plug out and kicked it over abunch to try and get the excess gas out. I took the top end off and cleaned all the carbon off cylinder head, piston and exhaust port. I did a compression test after and it read at 155psi. I lowered the float height and put it all back together and it fired right up and rides great. Thanks a lot for your responses and advice it is much appreciated.

[brawlingkhan]

After getting this machine running after sitting for some period of time it developed a lean condition. I noticed it would not want to return to idle very easily and it eventually turned into a run away engine that I could not kill unless I was in a 6th gear bogging it out. It seems as if left side has crank seal is leaking allowing air in the mixture, which is causing the lean condition. I have pulled the top end and the cylinder, piston, and rings appear to be in good condition so that was great news. However, I need advice on replacing the crank bearings and seals. Does anyone out here know a good replacement brand? Also, I am having some trouble getting the flywheel off.... anyone have a link for a good flywheel puller?

[ohgood]

After getting this machine running after sitting for some period of time it developed a lean condition. I noticed it would not want to return to idle very easily and it eventually turned into a run away engine that I could not kill unless I was in a 6th gear bogging it out. It seems as if left side has crank seal is leaking allowing air in the mixture, which is causing the lean condition. I have pulled the top end and the cylinder, piston, and rings appear to be in good condition so that was great news. However, I need advice on replacing the crank bearings and seals. Does anyone out here know a good replacement brand? Also, I am having some trouble getting the flywheel off.... anyone have a link for a good flywheel puller?

the tusk flywheel puller works fine. make sure you don't loose the key when the flywheel is off the crank though.

you'll have to split the engine cases to replace the seals and bearings. i would suggest watching a few videos on youtube before you start. lots of little tips here and there.

last weekend we reassembled a friends' kx80 (or 65, i forget) and used the 'hot slug' method when we were installing the crank to the case halves:

install seals
freeze bearings
freeze crank
warm case in oven to 200F, drop in frozen bearings to both cases (make sure seals are in first!)
freeze crank + left side case again (wrap in cold packs helps)
paint RIGHT side case joint with sealant, assemble transmission stuff in RIGHT side case
heat up (with torch) socket that fits into RIGHT side case bearing snugly until it's 'notchy' in movement
remove LEFT side case from freezer, drop it and crank, onto RIGHT side case (lube the seal) and bump down as needed while making sure transmission pieces stay aligned

test shift through all gears before the temperature difference is gone. if they all shift, great, install case halve bolts. if it doesn't shift, split it now (and swear a lot)

fill crank area with premix, check for leaks.
no leaks ? great, install top end
fill tranny with oil
no leaks still ? great, toss in bike
kick kick
Vroooom

[brawlingkhan]

Thank you for the advice, I plan to try this soon. Which sealant is ideal for the crankcase joints? I have used hondabond with success on other motors.