sudden lose of spark

i traded my perfectly runnin snowmobile(bad idea i think but we havent had any snow to ride so what the heck)for a 81 440 ltd belt that had been sittin but appeared b in good shape. we changed the crank oil cleaned the carbs twice and put some plugs in it along with 93 with fuel treatment the bike was dry when it was stored. the bike ran and drove but when it got hot you would lose all spark all of a sudden. if you let the bike cool for an extended period of time it would start again, it progressivley starting runnin worse right cylinder would fire then the left would kick but as the left picked up the right would quit and if the left was runnin good the right would stop completely. i took of the coil and it was cracked all the way around the case so i got a 2.2 ohms dyna coil and wires kit and installed it the biek ran dramaticly better witht he new coil but not perfect it would high rev and quit sometimes but idle relatively well with the choke just barely on. i thought i had solved my spark problem then it just quit on me all of a sudden again. i checked the spark and it quit completely on me again. i dont know if this is my cdi box or if it the electro magnetic box down inside the case that catches spark of the lobe on the end of the crank shaft. im broke and gettin married this year and if i spend 2 much money on parts my wife will kill me so i cant just go replacing parts. someone one plz help me figure this out its drivin me nutz

If not already done, would assure integrity of the igniter's ground connection through the black-yellow wire.

The ignition coil is supposed to "charge" while grounded through the igniter, and supposed to "fire" upon becoming ungrounded through the igniter.

Would also assure consistent full battery voltage at the ignition coil primary winding terminal when the ignition switch is ON.

Corrosion in a connector or a switch may impair conductivity.
Voltage from the battery to the coil first passes through both the ignition switch and through the "emergency" Off-Run switch. Either of these switches might be corroded inside.

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i borrowed a digital electrometer and the bike started and ran prty decent but not perfect i almost sure that its carb related thou. i took all my readings before i started it and while it was running. i was getting 10.8 volts out of the cdi box and to both wires going to the coil with the key on engine off (when i hooked these wire back up after replacing the coil the paperwork the came with the dyna coil said the position of these wires was not important since polarity didnt matter with single dual output coils, is this correct? and i got a 2.2 ohm dyna coil is this the right rplacement aftermarket coil?), and i was getting 11.7 out of coil and to both wires going to the coil with the bike running.I also was getting .8 volts out of both wires coming out of the stater and i had a good ground to the cdi box. the inside of the kill switch still looked brand new. ive cleaned the lobe on the end of the crank and the tab on the stater box, visually checked as many connections and wires as possible as well as fixed a questionable ground. after 10 min the bike quit again no spark at all still was gettin all of the same readings that i was getting out of the stater cdi box and coil wires as b4 when the bike was key on engine off. however i did not have the special test light you need that show temporary loss of power such as the cdi box temporarily grounding out the coil in order to make it fire so i could not test that, but i am goin to on friday any other help could be much appreciated i know how to work on things but electrical is definetly not my strong suite and im def not a motorcycle mechanic.

thanks all!!!! wishing i was riding instead of poundin my head!!! even though its still freezing.

81 440 ltd belt... erratic spark
10.8 volts out of the cdi box and to both wires going to the coil with the key on engine off -- That's insufficient. Should be 13+ volts matching battery voltage measured across the battery posts.

dyna coil said the position of these wires was not important since polarity didnt matter with single dual output coils, is this correct? -- Yes, that's correct.

got a 2.2 ohm dyna coil is this the right rplacement aftermarket coil? -- Yes, that's correct.

and i was getting 11.7 out of coil and to both wires going to the coil with the bike running -- That's insufficient. Should be 14+ volts matching battery voltage measured across the battery posts at 4000 rpm.

good ground to the cdi box -- That would be the "igniter" (not cdi), which igniter must have a good ground through the black/yellow wire.

after 10 min the bike quit again no spark at all still was gettin all of the same readings that i was getting out of the stater cdi box and coil wires as b4 when the bike was key on engine off.

It's possible that the pick-up (under the points cover) and/or the igniter is intermittently failing due to heat.
Could test while heating pick-up and igniter with a blow dryer to determine whether it accelerates loss of spark.
Or blowing these parts with cool air (from an air compressor) while the engine's running to determine whether it helps prevent loss of spark.

If not already done, would assure that the coil's primary winding terminals aren't shorting against any metal parts.

Good Fortune!

Might also check out these links:

www.armbell.com/forum/index.php?c=6&sid=...571a51a&mforum=kz400

www.kz400.com/

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when i went to buy a battery for the bike they looked up which one i needed in the book at walmart but it would not fit inside the battery box so i returned it for a smaller motorcycle battery that would fit could this possibly be my proble thank you for your help!

Would remove plugs, hold them grounded against the engine, turn ignition switch ON, and spin over the engine.

Look for fat blue sparks at plug tips. Which indicates that the spark is powerful enough.

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i know how to test the plugs for spark i am wondering if the wrong battery could be part of my problem, or if the charging system is not working properly if that could cause the sudden lose of spark. but i dont think its the battery cause it will not start even with the charger on it in the start setting on the charger.

440troubles wrote: i know how to test the plugs for spark i am wondering if the wrong battery could be part of my problem, or if the charging system is not working properly if that could cause the sudden lose of spark. but i dont think its the battery cause it will not start even with the charger on it in the start setting on the charger.

wondering if the wrong battery could be part of my problem -- not if it's providing enough power for fat blue sparks.

if the charging system is not working properly if that could cause the sudden lose of spark -- Nope, not unless the battery discharges to the extent that it becomes no longer able to provide enough power for fat blue sparks..

dont think its the battery -- Not the battery if it's providing enough power for fat blue sparks.

Good Fortune!

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440troubles wrote: i know how to test the plugs for spark i am wondering if the wrong battery could be part of my problem, or if the charging system is not working properly if that could cause the sudden lose of spark. but i dont think its the battery cause it will not start even with the charger on it in the start setting on the charger.

i dont think its the battery cause it will not start even with the charger on it in the start setting on the charger. -- Agreed. Provided the charger is functioning correctly and is properly connected. All predicated on lack of visible fat blue sparks on the plug tips regardless of 12 volt source (battery or charger or black magic).

The little green power-stroke guys residing inside the combustion chamber are looking for fat blue sparks on the plug tips. And they don't care where the voltage is coming from that supplies the fat blue sparks.

As known, there are numerous reasons why spark may be weak or absent or disappear or become erratic or intermittent despite existence of an adequate 12 volt power source.

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the bike produces a nice fat spark with a inline spark checker i am gettin ovr 12 volts to the coil, and to the cdi box, i tried replacing the igniter but that did nothing actually the bike didnt start at all, so i put the old igniter back on and the bike still didnt start at all(this is new) so what ever was intermittently failing has now failed, could it be the pulser coil(pickup) also the chargin system is workin properly supplying the battery with almost 14 volts while running but when the bike died the last time i got it to start the coil had almost 13 volts to it but when it quit and you tried to restart it the power goin to the coil got weak while cranking the engine any thought, im ready to take this bike for a long walk of a short cliff totally FUBAR