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Here's a new one for me; Have a 2010 Apex with the usual; yamcharger, PCIII, Ig. Mod, geared and clutched. 4 of us lined up on the lake last night and I got the jump on the others by a few sled lengths. End of run guys were all "Holy crap, you should have seen the flames coming out your exhaust." I ask them whether this happened at the beginning or end of the run. They said just after the start.
I believe that in positively aspirated engines, turbo and or supercharged, it's usually because even when the valves are closed the boost pressure is pushing the fuel/air mixture into the cylinders in their power/down stroke. In normally aspirated engines it's because when the piston is in its power/down stroke the suction pulls the fuel/air mixture in around the closed valve.... I think.
Is is possible that the yamcharger with only 2 lbs boost is enough to do this or is it the retarding of the timing? I don't think that this is a good thing anyway....looking for ideas before adjusting.
I believe that in positively aspirated engines, turbo and or supercharged, it's usually because even when the valves are closed the boost pressure is pushing the fuel/air mixture into the cylinders in their power/down stroke. In normally aspirated engines it's because when the piston is in its power/down stroke the suction pulls the fuel/air mixture in around the closed valve.... I think.
Is is possible that the yamcharger with only 2 lbs boost is enough to do this or is it the retarding of the timing? I don't think that this is a good thing anyway....looking for ideas before adjusting.
TBay Sledhead
TY 4 Stroke Master
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- Jan 16, 2005
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- Thunder Bay, Ontario.Ca
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- Snowmobile
- 06 Attak
01 SXR Long Track
I think it's the latter because 16.7 psi (atmosphere + 2psi boost) will not overcome the compression pressure never mind combustion pressure which would be in the hundreds of pounds.
Reverse
Extreme
So...what should one do?? Just leave it?? Don't notice any let up in power but concerned if this could cause damage anywhere else.
mr.pitstop
Expert
I ran mine hard down a long straight the other day. 1/2-3/4 throttle for a couple miles with wot for long stretches, when I got to the end and starting letting off (let off easy, I didn't just drop the throttle) I got a couple burps of flame out the exhaust.. I figured it was a combination of the hot engine/exhaust and some left over boost from the yamcharger pushing some fuel in as I let off.. But mine was at the end of the run, not the beginning.. That sounds odd...
fourload
TY 4 Stroke Master
It happens all the time on long lake runs!! Cool looking in the night!!
DUTCH OVEN
Extreme
Had it happen to me several times on long lake runs.
wileya
Pro
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- Nov 30, 2009
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- 125
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- Forest, Ontario
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- Canada
- Snowmobile
- 15 sr viper rtx se
had this happen to me tonight.... had it wide open for a good stretch and running it hard! looked like a cop was behind be or something! pretty cool when i looked back .
viperguy
Extreme
My Apex did the same thing. I had it at wide open for 2 miles and let off the gas and coasted to a stop and I looked back and flames were coming out the back of the exhaust. I hit the gas and they went out. Little worried that something was wrong.
Preacher
Expert
I also have had this happen . I had just summerized the fuel with marine stabil and I took a few rips on the railroad bed before loading up and headed home.( Last ride of the season) It was at night and It was quite a show. I think I have the name for Yamaha's next new sled. THE YAMAHA FLAMETHROWER 
FireStone
Pro
When you are WOT for 1-2miles long. 8 times on 10 you will have some flames...like a jet.
