Backfiring through exhaust...

ViperGeek

ViperGeek

New member
Joined
Dec 6, 2008
Messages
33
Age
40
Location
Eagan, Minnesota
Im having issues with my sled after i cleaned the carbs, cleaned the power valves, and while i was rebuilding the clutch thought i should start it up and let it run for a while to get the fuel through, after about 10 secongs of running, i hear a loud pop out the exhaust from cyl #1, even stretched the springs, and shuts down, i started it up again and it did the same thing, i pulled the spark plug and its dark and wet. what could it be, i adjusted the fuel screw 1 1/2 turns out, my jets are #1 146.3, #2 146.3, #3 150. Pilot jets are 47.5. Can someone give me some pointers, im wondering if it the spark plugs, they are not brank new, i put then in last season, and ran about 400 miles.....
 
I imagine that you have 1 cylinder not firing and the gas pooled enough in the exhaust to vaporize a little which ignited.

I suspect that one of your starter valves is not seating, or you have something missing or installed incorrectly in the carbs..

I personally wouldn't run it without the clutch, as it is designed to be balanced with that on. Of course simply idling it likely won't hurt anything.

They shouldn't do that at idle even if you had the airbox completely out.
 
Ding said:
I imagine that you have 1 cylinder not firing and the gas pooled enough in the exhaust to vaporize a little which ignited.

I suspect that one of your starter valves is not seating, or you have something missing or installed incorrectly in the carbs..

I personally wouldn't run it without the clutch, as it is designed to be balanced with that on. Of course simply idling it likely won't hurt anything.

They shouldn't do that at idle even if you had the airbox completely out.
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Might be a dumb question, but starter valves????were do i find them??
 
Some people call them chokes. Just follow the "choke" cable and you should find them. Technically they do not choke off the intake, but rather enrichen the fuel mixture by opening another fuel circuit in the carb. They are used for cold starting.
 
Ding said:
Some people call them chokes. Just follow the "choke" cable and you should find them. Technically they do not choke off the intake, but rather enrichen the fuel mixture by opening another fuel circuit in the carb. They are used for cold starting.
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Thats what i thought after looking at the carb exploded view. How do you fix the starter valve not seating/ take it apart and clean it again??
 
I'm willing to bet it is nothing more than a fouled plug (not firing). If you have left those plugs in from last year, and have done a lot of starts and stops, using a lot of choke, then it is likely carbon fouled. It will fire on occasion and ignite the raw fuel in the pipe as was reported above.
 
Essarex said:
I'm willing to bet it is nothing more than a fouled plug (not firing). If you have left those plugs in from last year, and have done a lot of starts and stops, using a lot of choke, then it is likely carbon fouled. It will fire on occasion and ignite the raw fuel in the pipe as was reported above.
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Ill get new spark plugs tonight, i completely rebuilt the carbs lat night, checked the floats, they are good, made sure all jets and parts are tight and clean, I still need to check to make sure the starter valves are clean, i havnt gotten to them yet.... Thanks, ill post an update tonight..
 
General Rule of Thumb:
Backfire thru pipe = Rich
Backfire thru carb = Lean
As most have said, check fuel screws, float levels ( set a little to lean side ), and check choke cable adjustments, change plugs.
 
snomoguy said:
General Rule of Thumb:
Backfire thru pipe = Rich
Backfire thru carb = Lean
As most have said, check fuel screws, float levels ( set a little to lean side ), and check choke cable adjustments, change plugs.
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How do i set the float levels to the lean side
 
ViperGeek said:
How do i set the float levels to the lean side
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try this...
http://www.totallyamaha.com/snowmobiles/aaTECH/carbs/guts_labled_small1.jpg
not hard at all...I use my fingers to hold float & take needle nose pliers & bend in direction needed...SET THEM @ 14mm...make sure you did remove your float pins & did in fact inspect your needle & seat area...if you have ring grooves on the needle, then they will need to be changed out, some spin them on on fine wet sand paper to save them...sometimes it works...most often not...good luck & keep us posted...
 
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Floats were all at 8mm, but i cant run it because the snowmobile shop gave me the wrong plugs, have to go back and exchange them, sux, ill post update tomorrow..
 
ViperGeek said:
Turns out i needed new plugs, my floats were under, needed to be set to 14mm, they were at 8, and motor runs great now, thanks
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Great to hear...drive her...
 
snomoguy said:
General Rule of Thumb:
Backfire thru pipe = Rich
Backfire thru carb = Lean
As most have said, check fuel screws, float levels ( set a little to lean side ), and check choke cable adjustments, change plugs.
Click to expand...



how can you tell if its backfiring from the pipe or carbs ??

thanks...
 
well went its backfiring in the pipe it make a big powwwwwwwwwwwwwwww and sometime it scared u lol
 
My viper use to backfire slightly through the exhaust when I would come to a stop sign or shut it down. When I checked the float valves they were starting to leak. I used a vacuum tester to test them. I replaced the float valves and no more backfiring.
 
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