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Old 12-23-2009, 02:00 PM   #1 (permalink)
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Newbie no spark on formula plus

Hi,
I have a 91 Formula plus 521 cc with a no spark condition. I couldn't find any generic "no spark troubleshooting" information in the stickies or anywhere else. I'm not used to 2 stroke ignition systems. I'm used to inboard boat engines that have distributor, points, condensor and a coil(certified technician). I don't know how to test without turning the ignition key on and checking for 12 volts. I couldn't find any numbers on ohming out the coil on this machine. I disconnected the kill switch and tether(assuming they ground out the coil, so if disconnected the machine should have spark). Maybe I'm wrong about those. Anyone have a troubleshooting chart or at least a wiring diagram for this machine? I turned the sled off to fill it with gas and that was the end of her. Any help would be appreciated, there's snow here and I have some time off!
Thanks!
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Old 12-23-2009, 02:07 PM   #2 (permalink)
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By the way, I did look at the service manuals link on this forum, but the closest year was 1985. I don't know what would have changed between 85 and 91. If anyone can, please let me know if that manual may still work for the 91 or if there were any changes. Thanks
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Old 12-23-2009, 02:22 PM   #3 (permalink)
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is it the spark plug that is fouled is it black and oily. try putting a new spark plug in that cylinder might fire for yea.
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Old 12-23-2009, 02:27 PM   #4 (permalink)
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sorry wrong reply i was reading another question about one cylinder not firing. ur best bet would be a manual i think theres one for ski-doo from 1990-1995 not very expensive can also find it online to download
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Old 12-24-2009, 06:18 AM   #5 (permalink)
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If you've already disconnected the key/kill switches, then the CDI is probably the problem. Luckily, aftermarket ones are pretty inexpensive.
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Old 12-24-2009, 10:08 AM   #6 (permalink)
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Are the coil and the cdi one unit on these machines? I haven't taken the coolant reservoir and oil tank off to see what is hiding back there. Any way to determine if the cdi went bad vs the coil? Will this run without the ignition switch plugged in? I disconnected the tether and kill switch, but I wasn't sure about the keyed ignition switch. Thanks again
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Old 12-26-2009, 08:13 AM   #7 (permalink)
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Yes, you can disconnect the key switch. The coil and CDI are separate units. The CDI is behind the oil tank. You may have to move the coolant reservoir as well.
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Old 12-26-2009, 01:26 PM   #8 (permalink)
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i replaced the cdi on my 93 plus and you must move the coolant tank to get at it.
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Old 12-28-2009, 02:28 PM   #9 (permalink)
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I have disconnected all key/kill switches and still no spark on either cylinder. Must be either the coil or cdi box. I pulled the coil off and I'm trying to figure out how to bench test it. When I took the coil off I noticed a brown wire just hanging there. I'm guessing that just came off the lower mounting stud for the coil, is that right? Anyone know a simple procedure on testing the coil?
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Old 12-29-2009, 10:27 AM   #10 (permalink)
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Can anyone point me in a good direction to find a CDI unit? I found used ones for a 1991 formula plus for $25+shipping but they were for a type 537 motor. I have a type 536, 521 cc motor. Would that work? I found aftermarket units from $75-200. Any recommendations? I found specs to test the coil from the 85 ski doo manual. I assume that they would have had the same coils. thanks
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Old 12-30-2009, 05:23 AM   #11 (permalink)
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Get the aftermarket one. Kimpex units are pretty good. Yes, that brown wire just goes to the mounting stud.
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Old 01-06-2010, 03:58 PM   #12 (permalink)
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I broke down and got a new coil and cdi box from denniskirk. I should only need one or the other, but I wanted to make sure I have everything i need. The coil is a parts unlimited, and the cdi is a kimpex. I put the new coil on first to see if that was my problem, and still no spark. Then I put the new cdi box on, and still no spark. I tried with the kill switches connected and disconnected, no spark no matter what. I'm $105 into this and I still don't have spark. Any ideas?
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Old 01-06-2010, 05:20 PM   #13 (permalink)
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Well, I found my spark problem. I had to cut the bullet connector on the aftermarket coil and crimp on spade connectors to match the CDI box and one had a bad connection. So now I have spark but the sled won't run. Think it's probably something stupid, I'll take another look at it tomorrow. I don't know which ignition component was actually bad, but oh well.
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Old 01-07-2010, 05:47 AM   #14 (permalink)
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Aslong as you have spark now. Change the spark plugs, they are probbly fouled from all that trying to start it before.
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Old 01-07-2010, 05:18 PM   #15 (permalink)
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This is killing me. I swapped out the plugs and still nothing. So I took off the exhaust and drained a half gallon of gas out of it. Pulled it over a bunch of times with the plugs out and exhaust off, then put everything back together and the engine fired for a second. Then back to nothing, guessing I'm having a flooding problem. I don't know if I have a stuck float or what. I'll pull the carbs tomorrow when there's some light.
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Old 01-07-2010, 06:12 PM   #16 (permalink)
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hi, this is for a 1989 but i think its the same.

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Old 01-08-2010, 05:46 AM   #17 (permalink)
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If that much fuel is in the motor again, the carb needles/seats are leaking by.
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Old 01-08-2010, 02:50 PM   #18 (permalink)
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Got it running this morning after leaving the fuel off for a while. I turned the fuel back on once it was running and drove it around for a while(a couple miles). It started bogging down, so I headed home. It died on the way there and when I checked the plugs the mag side was soaked. I still have spark on that side, so I took the carb off to see if I had a stuck float or some junk keeping the needle from seating. they were clean as a whistle. I'm going to go buy some more plugs and see if it happens again. What else could cause one side suddenly to flood? Up until my no spark problem the plugs had looked like they were both running the same, now there's definitely a problem with the mag side cylinder.
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Old 01-09-2010, 06:31 AM   #19 (permalink)
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See if you have fuel coming out of the impulse line from the fuel pump (the line that hooks to the engine block). If you do, rebuild the fuel pump and your troubles will be over.
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Old 01-12-2010, 06:08 PM   #20 (permalink)
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I checked the impulse line and everything is fine. I swapped out plugs to see if I just had a fouled plug, but that wasn't the problem. I tore the carbs apart again and checked the floats and needle and seat. everything is fine there too. I tried starting it today and it ran, so I went out for a bit. It ran perfect for the first 5 minutes, so I got on it a bit, went about a quarter mile and it started bogging. Gimped it back home and it died when I got there. One plug was dry and one was wet. Should I be looking at weak spark for some reason? I can't see why this cylinder is flooding when the carbs look perfect.
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