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hi i just recently bought a 1987 trx250x and it needed some rings so im working on this project guy i got it from said it was smoking at boscoe and it did good all weekend until the last day it cranked then cut off they took the head and jug off and said the rings was on top of the piston well i have a 2001 300ex atv and i just non running due to timing guides and tenchioner so i just took the piston and the jug and head and basically put a 300 ex top end on it ready to crank it but no fire we checked to see if it was getting fire by touching the wire and kicking it wouldnt shock me for nothing we took the coil off the 300ex and put it on there and it wouldnt fire any reasons why it may not fire please help!!! im 16 and i have a 20 year old brother we are working on it and i wanna get it up and going!!!!
 

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Welcome to the forum

First - have patience

No fire is an ignition problem. First thing to do is make sure the kill wire (black wire with a white stripe) is disconnected from the CDI unit. If that does not give you spark, then the problem is a bad CDI unit, bad pulse generator, bad stator or a bad coil. The coil is usually the last thing to fail. Pulse generators are easy to test. A blue wire with a yellow stripe from the alternator. Find out where it plugs into the wiring harness, unplug it, using a multimeter check continuity from the wire to ground - if you have continuity, switch the meter to AC voltage and kick the motor over to see if you have an output - if you have an output then you need to check the stator. Using the meter on AC voltage, check between the green and black wire with a red stripe where the alternator plugs into the wiring harness. Unplug the alternator wires and check output when kicking the motor over. If you have an output, then either the CDI unit is bad or the flywheel sheared the key on the crankshaft and the flywheel is out of time. Check the flywheel timing by taking the inspection plug out of the alternator cover - turn the crankshaft till the "T" mark is visible in the inspection hole. Place a soda straw in the spark plug hole, and turn the engine gently back and forth to make sure the piston is at top dead center when the "T" mark is in the inspection hole. If all checks out, you will need a CDI unit off an 87-92 TRX250X (or try your CDI unit on someone else's 87-92 TRX250X) to see if it's good or bad. A new unit is about $150 from Honda.

Good luck
 
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