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/cgi-bin/YaBB.pl General Category >> Rubber Side Down! >> Strange backfire /cgi-bin/YaBB.pl?num=1504656710 Message started by BGregg on 09/05/17 at 17:11:50 |
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Title: Strange backfire Post by BGregg on 09/05/17 at 17:11:50 Situation: after just starting my bike up and not letting it warm up very long the bike hates low throttle, low power and sometimes feels like it might die. Usually I just rev past this until it's warmed up further. Sometimes, two or three times ever, when I decellerate into this low throttle zone there is a weird backfire noise and it feels like a brake has been applied for a second. When this happens my initial reaction is that it was some sort of backfire thru the carb but I don't have the carb experience to know if I'm right. Thoughts what this could be? And is it my fault for not warming up beyond maybe a minute or two? |
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Title: Re: Strange backfire Post by IslandRoad on 09/05/17 at 18:20:13 You'll need to tell us a few more details. What year is the bike? How many miles on it? Is this a new thing that's happening? Have you made any mods (exhaust, air filter, re-jetting)? When did you last change or check the air filter? Have you checked the valve clearances? Do you use the choke when starting? On face value it sounds like pretty normal stuff for a cold bike. When mine's cold I usually use one notch on the choke, and keep the revs up a little bit when I come to a stop. After a couple of minutes it's warm enough. Back-firing from the exhaust is very common on this bike, but backfiring from the carb is not good - that could represent a timing issue. I'm sure the more experienced guys will offer advice once they have more info. |
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Title: Re: Strange backfire Post by Kris01 on 09/05/17 at 18:27:40 You probably have the factory tuned lean carb issue. Does the bike also surge at a steady cruise? |
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Title: Re: Strange backfire Post by IslandRoad on 09/05/17 at 18:28:44 And ... has the bike still got the stock fuel tap on the tank? It's known to fail, even on new bikes. It can cause issues that appear like weird carb issues. It can mess with the vacuum condition in the carb and/or starve the engine of fuel. Many members here have switched to a manual fuel tap from a Yamaha Raptor 660, as it fits straight on. |
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Title: Re: Strange backfire Post by justin_o_guy2 on 09/05/17 at 21:52:17 A bike that idles right all warmed up generally doesn't idle right cold. If you ride for twenty minutes, stop for a few minutes, restart, NOW howzit run? Low idle speed is really hard on the top end. Idling on the sidestand starves the cam for oil. |
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Title: Re: Strange backfire Post by IslandRoad on 09/05/17 at 22:16:44 637C7A7D60675666566E7C703B090 wrote:
Yeah, that's what I was tryna say ... it just took me more of them thar words! 8-) Same goes for the backfiring. If you tune away the backfiring on decel, then you're most likely running rich in any other condition. |
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Title: Re: Strange backfire Post by BGregg on 09/06/17 at 06:48:48 2005 Boulevard S40 ~7000 miles No drivetrain mods (so stock exhaust, intake, carb, etc.) Haven't checked or changed the air filter yet Changed the oil maybe 1000 miles ago Owned the bike maybe 3-4 months. |
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Title: Re: Strange backfire Post by BGregg on 09/06/17 at 06:52:46 Effectively stock everything, except for the led headlight I did this weekend. Bought it from an older lady so I'm assuming she didn't mod it. Runs great after it's warmed up. Occasionally it'll backfire on deceleration but this doesn't feel the same, this feels like an exhaust brake kicked in for a split second. Doesn't surge while on constant throttle, runs very smooth. Does the usual backfire on engine shutoff. |
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Title: Re: Strange backfire Post by justin_o_guy2 on 09/06/17 at 06:54:47 Common failure is the petcock. For about thirty bucks you can get a Raptor petcock, manual, plug the vacuum and avoid the hassle. Age matters more than miles on it. If you find fuel in the vacuum line, it's busted. If it runs better on prime, it's screwy. Low idle RPM doesn't oil the top end well. |
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Title: Re: Strange backfire Post by BGregg on 09/06/17 at 07:52:52 This is a new issue, maybe 3 times in the past week or two. It's always while the engine is cold, just starting out for a ride. Always when I roll back into the cold engine throttle dead zone. The scenario is usually that I'm riding in a parking lot in first and need to slow down to see if the way is clear or do a slow turn, I roll off the throttle, I can't remember if it's all the way off throttle or to a partial throttle, and get this backfire noise and the engine brakes aggressively for a split second. |
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Title: Re: Strange backfire Post by Todd James on 09/06/17 at 09:21:34 Hello BGregg You are describing the symptoms of an intake manifold air leak. Especially if the backfire sounds like a sharp crack. It will definitely cause the momentary engine braking you describe. It could be due to a faulty petcock, and you should go to the instructions in the Technical Documents to check it. (Better yet ... just replace it with a raptor and save future aggravation) There are also three things to check right now that are very easy: 1. Check the two screws that hold the intake manifold to the head. 2. Check the band clamp that holds the manifold to the carburetor. 3. Check the vacuum hose from the carburetor to the petcock. Be sure it is a tight fit on both the carburetor and the petcock and there are no cracks or holes along its entire length. I just took a picture of that area on my bike and included it below so you know where to look for these things. If the two screws are loose on the manifold you will need an offset screw driver to tighten them. (Picture is in the next post) |
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Title: Re: Strange backfire Post by Todd James on 09/06/17 at 09:23:26 Offset Screwdriver |
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Title: Re: Strange backfire Post by BGregg on 09/06/17 at 09:26:18 Todd, Thank you very much, I will look into this as soon as I can and report back findings. |
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Title: Re: Strange backfire Post by sagi on 10/07/17 at 16:04:30 BGress, Did you have a chance to try Todd's suggestion? I am noticing the similar issue? Mine is 2015 s40. |
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Title: Re: Strange backfire Post by sagi on 10/07/17 at 16:05:32 BGregg, Sorry mis-typed the name in the earlier post. |
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