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post #1 of 12 (permalink) Old 07-26-2019, 05:56 PM Thread Starter
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Trail Boss 330 Misfiring

My 2007 Trail Boss 330 starting misfiring a few days ago. I was riding and went to turn the headlights on while on a hill and accidentally hit the off switch and it backfired. It starting misfiring immediately after turning it on and continuing up the hill. Now it only seems to happen when going uphill or on rough terrain. I rode it today for 2 hours without a problem and then it started missing on the way home. Yesterday I changed the oil, oil filter, air filter and spark plug. Can this be from a dying battery or more likely a fuel problem? I currently run 93 octane and use the fuel within 2 weeks.
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post #2 of 12 (permalink) Old 07-27-2019, 04:36 AM
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Backfiring is most usually an ignition problem more-so than a fuel problem. When it's fuel system problem, it's usually associated with the fuel mixture being too rich.

Here's the ignition system trouble shooting guide as copied from the service manual:

IGNITION SYSTEM TROUBLESHOOTING

No Spark, Weak or Intermittent Spark:
No 12 volt power or ground to CDI unit
Spark plug gap incorrect
Fouled spark plug
Faulty spark plug cap or poor connection to high tension lead
Related wiring loose, disconnected, shorted, or corroded
Engine Stop switch or ignition switch faulty
ETC switch mis-adjusted or faulty
Poor ignition coil ground (e.g. coil mount loose or corroded)
Faulty stator (measure resistance of all ignition related windings)
Incorrect wiring (inspect color coding in connectors etc)
Faulty ignition coil winding (measure resistance of primary and secondary)
Worn magneto (RH) end Crankshaft bearings
Sheared flywheel key
Flywheel loose or damaged
Excessive crankshaft runout on magneto (RH) end - should not exceed .005″
Faulty CDI module

I would start with checking the connectors at the LH handlebar switch assy. - I have seen many faulty connectors cause any number of problems including cranking but not starting and intermittently dying. It's likely it could cause backfiring too. An easy test is to disconnect the black wire at the CDI unit (the black wire is the kill wire) - if you disconnect it, you cannot stop the engine until it is plugged back in, but if you disconnect it and the engine quits backfiring, then the problem is in the kill circuit which includes the key switch, handlebar switch, throttle safety switch and reverse limiter.

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post #3 of 12 (permalink) Old 08-30-2019, 03:59 PM Thread Starter
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Thanks again latebird. I’ve cleaned the carb, new spark plug, air filter and battery. I can’t find this black wire on the handle bar. I have a bunch of wires that go to the left handlebar with a black cover around them, i have a aftermarket kill switch in the middle part of the handle bars. There’s no backfire when the engine is cold, then about 5 minutes of driving it backfires out the carb under pressure. Runs fine in neutral. I tried taking the lid off the air filter box and it becomes a lot worse. Any help is appreciated, thanks.
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post #4 of 12 (permalink) Old 08-31-2019, 05:41 AM
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Backfiring out the intake usually indicates a lean condition in the fuel system and if taking the air box lid off makes it worse, it more or less confirms the lean condition. Does the air box have the snorkel still attached? If not, install a snorkel and it may help. If it does have the snorkel, try putting two layers of shop towel over the opening and see what happens. If layers of shop towel over the opening to the air intake seems to solve the problem, then jet the carb accordingly. If the problem is only above 1/2 throttle, then just increase the main jet about 2 sizes up from what it currently has. If the problem in only between 1/4 and 3/4 open, raise the slide needle one notch. That brings up the question of does it have the OEM Mikuni carb or a Chinese POS replacement? If it's a Chinese carb, it may have unmarked jets and unknown jet sizes. Not only that, the Chinese carbs may have different threads than the OEM carbs and Mikuni jets may not screw in. Even if the Mikuni style jet will screw in, the size of the jet may not compliment the size of the air passage, so just getting the correct jet size from Polaris may not solve the problem. The std. Mikuni jet could be either too large or too small depending on the size of the air passage.

Let me know what you figure out using the shop towel method of restricting the intake air flow.

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post #5 of 12 (permalink) Old 08-31-2019, 08:36 AM Thread Starter
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I used 2 paper towels as a substitute for shop towels. It has the snorkel on the box lid and I have the Mikuni carb still. I taped the paper towels to the snorkel to cover it while riding. Less than 1/4 throttle it Boggs and stalls. I also tried holding speedo reverse and loosing the gas cap, neither helped. Ran fine for the first mile when it was cold without the paper towles. Then it continually gets worse, no power at all and constant backfiring through the carb. Worse with 2 riders on as well or with a heavier rider.
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post #6 of 12 (permalink) Old 08-31-2019, 09:52 AM
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It's not made for two riders - don't do it

Regardless, it sounds like it is worse when hot and under a load - what spark plug did you put in it?

Also, a bad battery could cause the problem - it has a DC CDI - if battery voltage is falling, it will affect the ignition what is the battery voltage when cold before starting, what is the voltage when hot and idling and what voltage do you read when the engine is hot and running about 3000 RPM?

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post #7 of 12 (permalink) Old 08-31-2019, 10:11 AM Thread Starter
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Engine voltage off is 12/13, on and idling is 12/13 and running over 3000rpm is 14/15, the spark plug cap seems a little deteriorated, I would need to buy the whole ignition coil to replace it from Polaris or could I use an aftermarket one?
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post #8 of 12 (permalink) Old 08-31-2019, 10:15 AM Thread Starter
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The spark plug is a NGK R BKR6e
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post #9 of 12 (permalink) Old 08-31-2019, 05:52 PM Thread Starter
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i just noticed that my fan isn’t working either, temp light isn’t coming on and it definitely seems like it’s over heating
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post #10 of 12 (permalink) Old 09-01-2019, 08:09 AM
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Since your fan is not coming on and the hot light is not working, it sounds like the SSCB module has failed. It might be going into limp mode when it gets hot.

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