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Discussion Starter #1
I'm working on a 1986 polaris trail boss 250 and cannot get a spark to the spark plug. I have replaced the ignition coil, CDI, spark plug, stator, voltage regulator, reverse speed limiter, and every cable. I was reading through the service manual and the test of the stator said, "check between white/brown and white wire to get 120 ohms". When I tried this check I received an open circuit. When I checked between the black/red and white/brown I got 120 ohms. So, does anyone know if the new stator (OEM) could have the cables backwards or is there something else I need to test?

Also, the only new CDI I could find was a high performance OEM part so I don't know if others have had issues with those.
 

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Have you tried just unplugging the black wire on the CDI to see if you get spark?

However, if the wiring diagram is to be believed; check the white stator wire to brown wire and continuity should be near zero - like wise brown the the engine case will be near zero and white to the engine case will be the same. Brown/white to the engine should be 120 ohms - likewise to the brown wire and the white wire.

137783


If you don't get any continuity on the brn/wht wire, replace the stator.
 

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Discussion Starter #3
The stator checked out. I pulled the air box off and found the carburetor was blowing out instead of sucking in. Have you seen this before?
 

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It's actually normal - a piston port two stroke blows some crankcase air out the intake as the piston travels downward before the piston closes the port - it's why the reed valve was introduced - to shut off the reverse flow of air as the piston compressed the crankcase - now, the flow of air can be excessive if the piston does not fit the bore properly or is broken and not closing the port at the right time - it will not affect compression a great deal, but it can prevent the engine from running or running properly.

With the carb off, rotate the engine by hand while looking in the intake port to examine the piston skirt to see if it is intact or broken.

But this has nothing to do with not having spark. Have you got spark now?
 

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Discussion Starter #5
Sorry I thought I'd through that question out there too real quick since I noticed it.

Unfortunately no on the spark. The way I am testing the spark plug is connected the spark plug to the plug and touching the body of the spark plug to the top of the motor as ground. I cannot visibly see a spark. I put a multi meter on the plug to see what voltage was coming out and received .1 volts AC (and DC).

I'm not sure if the problem is one of the OEM parts I used as replacement (stator, CDI, and ignition coil). The flywheel looked to be in good shape and so did the magnets.

I did test the stator per what you said and the values matched. I also pulled the black wire from the CDI and same thing.

This is the first time I have worked on an ATV so I could just be going about the problem wrong.
 

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You can't measure voltage to the spark plug with a std. volt meter - you need a peak voltage meter or a peak voltage adapter to read the voltage on the DC scale or an oscilloscope to measure the peak of the voltage spike produced by coil - normally 35,000 to 45,000 volts at the spark plug.

For the novice, lift the spark plug above the cylinder head and crank the engine over - the spark should jump from the plug to the head 1/8 to 1/4 inch minimum - a good spark can jump 1/2 inch or more.

Where did you find new OEM parts? Nothing is available from Polaris and hasn't been for years.
 

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Discussion Starter #7
I got all the OEM parts from Ebay and RMstator at the below links.




Do you see an issue with one of these I purchased?

I tried testing the spark plug as described and there was no spark jumping.
 

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No, I don't see a problem with the components - have you checked all the ground connections? How good is the ground between the engine and the frame? The engine is mounted with rubber cushions and has a belt drive - the coil is mounted to the frame and the spark plug is in the engine - spark has to get from the coil to the engine and travel through the ground connections back to the coil.
 

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Discussion Starter #9
I checked continuity between the frame and the engine and got a ring on my multimeter. I see two ground connections. One from the engine to the negative terminal of the battery and a ground from the voltage regulator and the bottom of the engine (or frame couldn't get a good look). Is there more than those 2? Even though I have continuity do you think I need to sand the connections and try again?
 

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What was the ohms read between the components? Less than 0.1 is good - more than 2 is bad - I'm thinking that once all the check have been made it will come down to the stator being defective or the magnets in the flywheel, but before you start pulling things off, how did you determine the coil and the CDI needed replaced, of was it like "if I replace all the parts it will work"?

Maybe try the old CDI and coil to see what happens - if you tested and determined without a doubt that the coil was defective (open winding), the don't retry it - there is basically 5 parts to the ignition beside the wiring and connections - the charge coil on the stator, the CDI unit, coil, plug cap and spark plug. If all the parts are new and the grounds are good and you still don't have spark, then there is a bad part or connection somewhere.
 

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Discussion Starter #11
My method was in fact replace one piece at a time until I get spark (stator being last). What is the proper way to check the ohms value between each component?
 

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The proper way is to use a meter that can be zeroed with the leads connected - most cheap meters are self zeroing - so take a piece of wire and connect it to the battery neg terminal - connect one lead of the ohm meter to the battery terminal and the other to the end of the wire - record the reading - this is the resistance of the wire and the meter leads - disconnect the meter lead on the battery terminal and check each component that is grounded either to the metal pert of the component or the ground wire (brown) where it attaches to ground - check the wire, not the fastener that connects the wire to ground - deduct the reading you got when you checked the lead resistance - anything under 2 ohms is good - also check directly to the engine (like the cylinder head) and see if the resistance is nice and low - if you get a reading over 2 ohms after subtracting the tare reading, repair the ground connection - many times simply loosening the fastener and retightening it is all that's required. Once satisfied the connections are electrically solid, you will have to get a peak voltage tester to find out which component is not doing what it's supposed to.

You should get appx. 35v peak from the CDI charge coil, 2 to 3 volts from the pulse coil, appx. 100 volts from the CDI box to the coil and 35,000 to 45,000 volts to the spark plug.
 

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Discussion Starter #13
So it turns out a wire was backwards on the CDI. I now have spark! I can not get it to start still but I need to most likely adjust the stator for the timing same with the flywheel. I also need to look into the carb blowing out like you already explained. I greatly appreciate all your help up to this point. I will probably have more questions soon. Thank you
 

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Discussion Starter #14
Just to provide an update since you provided a lot of help. The ATV is up and running! You were right about the piston. There was only 60 psi on the engine so I had the cylider bored and a new piston put in. The electrical system works like a charm too (since it is 100% new). Thank you again for the help.
 
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