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Discussion Starter · #1 ·
Hi guys, I have a 400ex my son drives was running good then all of a sudden wont run. I took out the spark plug cranked it over seems to be sparking little but dont think its enough. I sprayed starting fluid in the spark plug hole put the plug back in and it wont even fire. I downloaded the repair manual and started to check things out. I'm only getting about 44 volts at the coil when i crank it over. suppose to be 100v per manual. i checked the coils ohms and it is good. I checked the connection from the motor stator and still only 44v. i would think the stator is bad but the ohms test came out normal. Is it possible for a stator test to come out normal but not enough volts when cranking it over? Does anyone know what the ohms is suppose to be at the stator for sure? Please help don't want to buy a stator if thats not the problem they are expensive.

any suggestions appreciated and thanks.
Dave
 

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If you notice - Alternator exciter peak voltage and Ignition coil primary peak voltage is the same - 100 volts minimum PEAK. This is AC voltage and needs to be measured with an oscilloscope.

If you suspect a weak spark, crank the engine and move the plug away from the head. A normal spark will jump from the plug to the head up to 1/2 inch. If this is the case, try a new spark plug. If the spark will not jump from the plug to the head, remove the spark plug cap and see if the spark will jump from the wire to the head up to 1/2 inch. The plug cap has a 5K resistor built into it and the wire to the coil is wire, not carbon fiber.

The fact that you have spark pretty much eliminates the CDI unit and coil as a problem, but the best test is to try (known good) parts from a running machine. If you swap out a part (coil and/or CDI unit) and it runs again, then you have solved the problem.

There is no accurate test for a stator. A friend of mine lost spark on his 200 - he tested everything "by the book" - the only part that tested good was the stator. After replacing the pulse generator, cdi box and coil, he still had no spark. Finally he replaced the stator and solved the problem. The only part that tested good was bad.

There is also the possibility that the flywheel key sheared causing a weak spark - if the key sheared, you can check by using a straw through the spark plug hole and turning the engine with a wrench to find TDC and check to see that the mark on the flywheel is where it is supposed to be.

Good luck
 

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Discussion Starter · #3 ·
Hi, Thanks for the reply. You can't test voltage on a Multi-Meter? I tried cranking over the engine and spark will jump to the head holding it about a half a inch away. Man i'm stumped i have rebuit engines b4 but this has me confused. it sparks but not as much as my 200 road bike. I dont want to just keep throwing money at it can get expensive for coil,cdi box, and stator.
Thanks Dave
 

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Start over - if you have spark, spark at the right time, compression, fuel and air in the right amounts, it will run - it's a machine, it has to - you are missing part of the formula.

If you don't have a compression gauge, just check the valve clearance. Valves have a tendency to get tight, drop the compression and prevent the engine from starting. If the valve clearance is excessive, you may have other more involved issues.
 

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Hey everyone, so i had this issue as well and it was self inflicted due to my stubbornness. I have rebuilt the motor on mine 3 or 4 times and i can do it with ease and not think twice now, i’ve even split the case. Upon my last rebuild I just couldn’t get it to fire to save my life. I refused to believe i could’ve screwed something up because i’ve done it so many times. I threw parts at it, new ignition coil, new carb anything i could think of. The weirdest part was when cranking over I couldn’t even get the damn thing to fire one time like you would normally get, not even a backfire. After a week of this shit, i set the fly wheel to tdc(top dead center) and pulled the valve cover off. Sure as shit it wasn’t lined up, I had timed in completely 180 degrees off and that causes exhaust valves to be opening when it should be intake vice versa and so on. Fixed that threw it all back together fired right away. Long story short second guessing yourself is never a bad idea and a big ego never helps.
 

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I had timed in completely 180 degrees off and that causes exhaust valves to be opening when it should be intake vice versa and so on.
Sorry, but that makes no sense - to be off 180 degrees, you would have to time the cam at BDC (bottom dead center) - the ignition fires near TDC on both the compression and exhaust stroke (referred to as 'wasted spark ignition') - the cam turns at 1/2 the speed of the crank, so if the cam is 180 degrees out of time at TDC, just rotate the crank 360 degrees (one full rotation) and the cam will be in time. There is no such thing as being 180 degrees out of time on the cam. Fromm TDC to BDC the camshaft rotates 90 degrees.

Think about it and revise what was wrong - it was not the cam timing - it was something else that you may have corrected in the process, but it was not the spark timing. That is set by the crankshaft and it fires every 360 degrees.

But congratulations on getting it going.

BTW - it's not a good idea to respond to 6 year old threads. Several members have died in the years since this was posted and the OP has not been seen on here since 2015.
 
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