My Sled Backfires Then Won't Start [Archive] - Snowmobile World : Your #1 Snowmobile Forum

: My Sled Backfires Then Won't Start

01-17-2004, 08:21 PM
I Went to go sledding today :D

My bros has tried to start the sled the past 3 days

it starts then backfires after acouple of minutes

So today I went to start it

It started allright

Then backfired the filter on top of the airbox flew about 8 feet in the air :dazed:

would not start after that :cussing:

So I took the carbs off to clean them,the back of the airbox was split open,I guess from the back fire :lookaround:

Cleaned the carbs :)

Put them back on and started the sled again and it back fired again :cussing: then would not start

So I call the Doo dealer the service guy says it might be the coil :confused:

What do you think? SWRules

I am baffled :huh:

01-18-2004, 04:40 PM
thats a good one! i can picture that foam sponge popping into the air. as for a fix..dunno. backfiring that bad out the carb is usually lean on fuel or timing way off. i know neither of those you probably fiddled with though. bad coil usually causes intermittent loss of spark after warm up...but that is not a rule set in stone. i guess try a coil from another sled and epoxy your airbox back together. is that sled reed or rotary valve induction? broken rotary valve or valve timing off?

01-18-2004, 08:05 PM
How would I check the timing? :confused:

Its a rotary valve 583

Could it be sucking air?(carb boot)

It ran good on the monday I put about 40miles that day

Bros put another 15

But on tuesday he said the sled started he let it wamr then went to leave it backfired

Tryed wednesday and thursday and all it did is start then backfire

So I clean the carbs saturday

It has stock jets

Will check compression tomorow and try another coil before buying a new coil

thanx SWRules

01-19-2004, 10:21 AM
TTT :)

01-19-2004, 12:27 PM
It could possibly be the cdi box.

01-19-2004, 05:00 PM
bad cdi will usually mean no starts. you will have to go to the manual for motor timing or rotary valve timing...complicated. try the simple stuff first. my bet is still bad high tension coil.

01-19-2004, 05:59 PM
That is a good one!

I have a hard time thinking it may be the coil. It can cause problems, but it certainly won't make a cylinder fire early and it has to fire to early to blow thru the carbs. Have you checked the plugs? I assuming you did, but I don't see where you say whether you did or not. I would check compression first and look for a broken ring or a hole in the piston. No dents or obstructions in the pipe? It could be the CDI, but I doubt it. You might also want to check to be sure that when one piston is at the top, the other is at the bottom where it is supposed to be. Rotary valve timing won't make it backfire.

Give us all the details - year, model, miles, work done, etc. I'll look into it a bit more when I have all the details.

01-19-2004, 09:46 PM
Stock 1995 STX 583 :D

14,000kms :)

365km this year so far :)

no rebuilds,cleaned RAVE valves(clean btw) 125psi both sides in Nov,but will check compression this week

Stock jetting

I have the 1995 Skidoo manual

Cleaned the TRA last week,clutch bolt used to get loose(previous post in tech btw)

Bros has been fouling plugs right and left before this situation,he says both sides one day PTO another day Mag

BTW like I said before I have never fouled plugs on it I have had it for 3 yrs

Once he put new plugs it would run fine

But not this time,tryed all the old plugs still no go

Prime it it starts then goes to die out and then backfires :dazed:

The sled is stored outside ,tarped of course

Temps have been -28-36c at night and -17-26 daytime,maybe ice in fuel :confused:

I just brought the sled to my bros inlaw into the heated garage to thaw out tonight,will drain gas from tank :sly: and put some fresh gas

No dent in pipe/muffler

Have recoil from older 503(doo recoil are POS),3rd recoil in 3yrs

Clean carbs Saturday and still no go

01-19-2004, 09:50 PM
Let us know what you find for compression and degrees between PTO and MAG TDC.

01-20-2004, 03:32 AM
ive never been ito these motors a wole lot, but how does the ignition trigger work?...magnet style crank snesor trigger?...ive seen those come loose and move around, causing the ignition timing to be off...but im not sure..i havent been inside yet. Check the primary windings?...see that everything is sound under the recoil magneto. If its firesoming out of the intake, its gota be firing before the piston closes the intake port off. Unless there is a way for one firing cylinder to backfire thorugh the other cylinders intake due to a broken rotary valve?...since there is only one valve for two Cylinders?....ideas, but i havnt been inside yet...

01-20-2004, 10:45 AM
We had the exact same symptoms with a 670 recently.

Turns out that a piston (PTO side) was gone (bad gas suspected).

If your compression is still good, then look elsewhere for the problem -- wires maybe?.

Good luck!

01-20-2004, 11:16 AM
Sounds like when my piston rings let go.
All it would do is backfire.
Compression test will reveal alot :slick:

01-21-2004, 11:47 PM
Well it has been in the heated garage for the past 2 days thawing out :)

New set of plugs 3 primes one pull she started.let it idle for a few minutes :thumbsup:

Stop it then I restarted it,no problems

So my guess is ice in the fuel :slick:,might of plug fuel filter???

Took my recoil apart after and the lil plastic thing below the spring is broken again :cussing:

Will change fuel lines tomorow,put fresh gas,go for a ride to see how it runs

01-22-2004, 01:16 AM
Water in the fuel. Had something very similar happen to a riding buddy's FIII.

01-22-2004, 08:11 AM
Frozen Ice would of been my guess to FB as I have had the same thing happen to friends at my place , especially Dpaiges sled every morning. The fix for me is too put a hairdryer on the fuel pump inbetween the carbs for 5-10 minutes, unthaws them everytime. IF no hairdryer is readily available then hot water can be used. OH and always run ISO in every tank too.

01-22-2004, 09:51 AM
What is ISO?
Is it Isopropyl Alcohol?
What ratio do you use?

01-24-2004, 08:41 PM
:cussing: :cussing: :dazed: :cussing:

Well here we go again

I guess it was the new plugs that made it run good

It was all warmed up to go today and then BBBBBAAAaaaaaaa :cussing:

Plug on the mag has weak spark I think?

Once it gets wet(not rich btw) it won't fire

new plug runs fine for a couple of days then same ole same ole :cussing:

Put about 60kms+ last night and ran great

But this afternoon :cussing:

Stator coil? is that the trigger coil?

How much would a shop $$$ to get them to diagnose the problem properly?? :confused:

Once I know its a certain thing,i would be able to tackle it,without buying stuff I do NOT need?

Sorrry for bringing this up again,but my sled needs a good @$$whooping soon :p

paul yarek
01-24-2004, 11:33 PM
Originally posted by FreezerBurnt@Jan 24 2004, 08:41 PM
Sorrry for bringing this up again,but my sled needs a good @$$whooping soon :p
marriage life is getting to you :huh: now you are beating on your best friend. :ohmy:

01-25-2004, 06:25 PM
:cussing: Paul :p :lol:

Maybe the sled heard I was thinking of selling it in Nov and decided if it runs like crap I won't get much for it and keep it :dazed:

Mind you NEW 2003 XC 700 is going for $5999ca here in Sydbury at THE SHOP

I don't know arrrg

I am really happy with my STX till this lil problem