xc sp 500 problems, cdi maybe? - Snowmobile Forum: Your #1 Snowmobile Forum

xc sp 500 rider · 11-01-2009, 07:52 PM

hi,

took my sled out for a ride around the house and it is running very crappy, it is back firing and not just running right, my dad thinks its the cdi, or the throttle block saftey switch, can you test these, if so how? he doesnt think anything is wrong with the motor hes pretty sure its electrical. we put in new plugs and cleaned carbs.

thanks!

JheLrey · 11-01-2009, 09:35 PM

Did you let it get up to temp? Mine backfires every so often and because this sled is new to me, I can't tell you much more...

xc sp 500 rider · 11-02-2009, 07:22 AM

ya, and it idles just fine.

mrholmquist · 11-02-2009, 07:36 AM

if you think the throttle safety switch is causing the cutting out make sure the throttle cable is not too loose. Adjust the cable to between 0.010" and 0.030" free play at the throttle block. Many people disconnect or bypass this safety switch when all that is needed is a simple cable adjustment.

Other suggestions I can offer is a compression test , check piston skirts and also
plugs and plug caps. If the main jet was plugged in one or more carb it could idle ok but not deliver fuel when the throttles are opened. try to narrow down wheather the backfiring is coming from one particular cylinder. Pull the air box and see if it is backfiring through one of the carbs or both

XLT Spartan · 11-02-2009, 09:49 AM

It sounds like your carbs are not properly adjusted. I would start there. Make sure your air screws are set correct (should about about 1 turn out) and everything is synced. It's totally possible that it could idle correct and then backfire when you ride it if this is not right. If the engine is cutting out then it could be the throttle safety switch, but if it's just rough and popping it's probably the carbs adjustment. You may have a combo of both.

JDS · 11-02-2009, 12:23 PM

It's not the CDI. Check for a mouse house in the exhaust or intake.

ppolaris1010 · 11-02-2009, 01:14 PM

Here is the best way to check if a switch is bad and causing it to lose spark for a second.There is a single black wire with a white connector it should be down by your pull cord where it goes into the motor.You might have to take the airbox off to find it that will disconnect all your shut offs and safety switches.When you unplug it you wont be able to shut the sled off until you plug it back in.If the problem goes away with it unplugged then you know one of the switches is bad or adjusted wrong. If it still does especially when it gets hot then its probably your cdi. Or like jds said a mouse got into it.Check under your handle bar cover they love it in there. If your still unsure try choking it when it starts to backfire see if that helps it could be a fuel problem but not to common with backfiring could be a lean misfire.

polaris rider · 11-02-2009, 02:45 PM

throttle safety switch is more a prob with ACs.. and maybe it was jsut backfiring cuz it was warm? What was the temp outside? And my sled has backfired on me about 4 times, and ive started it about 15

TwinsofMLB · 11-02-2009, 04:15 PM

If it's too warm you'll definitely get backfire and poor performance...

xc sp 500 rider · 11-02-2009, 04:29 PM

about 20 degrese its not to warm! there are no mouse chewed wires or mouse houses in the exhaust pipe, the carbs are totally cleaned, runs good on both cylinders , and it just had a new top end, we took apart the airbox to clean the carbs, and it has new plugs and good spark, its got to be either the throttle saftey switch, cdi, carbs not right or throttle cable loose. is it possible to test cdi without putting a different cdi on the sled and seeing if i still have probs? ill unconnect that black wire and see if its one of the switches.

xc sp 500 rider · 11-02-2009, 06:47 PM

if it is a mouse nest in the exaust pipe how do you get it out because it seemed to run better strait piped. so there might be one in the can

tundrapolaris · 11-02-2009, 07:20 PM

What will cause backfiring is poor compression on a cylinder. After sitting all summer i've seen rings slug up and seize causing low compresion. They will idle but when reved it will bypass. My 600 sp did it. You can pull a exhaust valve and look inside for abnormalities.

xxxthebxxx · 11-03-2009, 05:33 AM

Quote:

Originally Posted by xc sp 500 rider

if it is a mouse nest in the exaust pipe how do you get it out because it seemed to run better strait piped. so there might be one in the can

take off the exhaust and look inside.

xc sp 500 rider · 11-14-2009, 12:58 PM

i ran it today and disconnected the wire that turns off all the switches it did not help, it sounds like a lean misfire to me, and my dad thinks one cylinder isnt getting fuel. any ideas?

**RJ Gleason** · 11-14-2009, 01:08 PM

Check the plug color to be sure.

xc sp 500 rider · 11-14-2009, 01:13 PM

dad told me same thing!

tundrapolaris · 11-14-2009, 06:22 PM

Have you done a compression test yet? I still think you have blow by.

polaris rider · 11-14-2009, 08:15 PM

yea id check compression.. could have blown a cylinder

xc sp 500 rider · 11-25-2009, 12:14 PM

it was just rebuilt (1 mile on rebuild) by the person we bought it from and me and my dad took it apart to make sure he did it right luckly we did he put the rings on upside down so they didnt fit right.... anyways the compression is about 120 in each, both plugs are about the right color and after running it both sides of the y pipe are hot so it must be running on both cylinders. it idles anywere from 1800 to 1200 rpm and doesnt really engage until nearly 4000rpm is this right?
thanks, josh
also how come i cant see any of the avatars or anything there is just a small white box with a red X in it ?

**RJ Gleason** · 11-25-2009, 02:00 PM

Quote:

Originally Posted by xc sp 500 rider

it was just rebuilt (1 mile on rebuild) by the person we bought it from and me and my dad took it apart to make sure he did it right luckly we did he put the rings on upside down so they didnt fit right.... anyways the compression is about 120 in each, both plugs are about the right color and after running it both sides of the y pipe are hot so it must be running on both cylinders. it idles anywere from 1800 to 1200 rpm and doesnt really engage until nearly 4000rpm is this right?
thanks, josh
also how come i cant see any of the avatars or anything there is just a small white box with a red X in it ?

The idle range and engagement is good.
See, good thing that you checked his work.

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