October 13th, 2013, 10:15 AM | #1 |
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Loud crack on cold startup
Hi,
The past two times I have started my 250 in colder weather (55F) there has been a loud pop from the exhaust. The bike seems to run normally. Is this something to be worried about? Thanks Ben |
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October 13th, 2013, 10:20 AM | #2 |
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If it sounds like a misfire, the bike may need some valve adjustment and some carb cleaning, because those are caused by lean mix of air-fuel or poor sparks.
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October 13th, 2013, 10:26 AM | #3 |
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Ok, I was planning on shimming the carb needles but it got put off. Would that help?
Thanks Ben |
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October 13th, 2013, 10:42 AM | #4 |
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Yes, it could, but only if fuel is not restricted to flow through the several jets and passages.
The needless don't do much for start ups, they are more influential at middle range. It seems that your fuel restrictions are for the idle and choke circuits. Checking the flow through the petcock won't hurt, just in case you have restriction due to filters or poor vacuum. When the air is cooler, the mix gets more air than fuel and burns slowly, producing that boom while the exhaust valves start opening.
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Motofool .................................Never ride faster than your guardian angel can fly "Mankind is composed of two sorts of men — those who love and create, and those who hate and destroy. Love is the bond between men, the way to teach and the center of the world." - José Martí |
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October 13th, 2013, 12:55 PM | #5 |
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ok awesome, thanks!
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October 13th, 2013, 02:03 PM | #6 |
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Where are you setting the choke when you start it?
I'm thinking you may have more choke than you need for the temp, and backing it off some may cure the problem. |
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October 13th, 2013, 11:06 PM | #7 |
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October 14th, 2013, 07:03 AM | #8 |
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Wasn't there a thread that said this was normal for newgens?
http://www.ninjette.org/forums/showthread.php?t=15025
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October 14th, 2013, 10:17 AM | #9 |
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Normal thing. Happened just the other day to me; this time I was ready for it
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October 14th, 2013, 11:14 AM | #10 |
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i learned recently that coils that are going out, when cold, don't produce a good spark. so when i started getting some backfire on cold starts, i first wrote it off as nothing, maybe old plugs at worst. turns out one of the connectors on one of the coils was broken. replaced the coil and haven't had the issue since.
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October 14th, 2013, 08:28 PM | #11 | |
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Quote:
But can that explain the pop right at the moment the button's pushed to start the bike?
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October 15th, 2013, 05:28 AM | #12 | |
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Quote:
It only takes one of those happening late to produce a loud boom. I have seen mufflers completely opened by the instantaneous increment in pressure generated by one of those (that is why cylinder's walls and piston's heads must be thick and strong). I don't believe that any exhaust or intake pop is normal for pre or new gens; they are symptoms of something out of whack and I wouldn't just ignore it. If the mix is too lean or too rich at start ups, or if the sparks are too weak, then they cannot be optimal at normal operation and high rpms'. Learn more here: http://en.wikipedia.org/wiki/Back-fire
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Motofool .................................Never ride faster than your guardian angel can fly "Mankind is composed of two sorts of men — those who love and create, and those who hate and destroy. Love is the bond between men, the way to teach and the center of the world." - José Martí |
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October 16th, 2013, 01:22 PM | #13 |
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Ok thanks for all the replies. I ended up putting in the two washers in the carb needles anyways. Now Im having a problem keeping a steady speed. Acceleration is more flat. When i try to maintain a speed with minimal throttle input, It seems like the engine is missing a LOT of combustion cycles and I get this super low pitch bass sound. It almost sounds like someone humming a really low note.
I was thinking that 2 washers was too much and I either need to take one out, or lean out the fuel mixture via the carb screws. any suggestions? Thanks Ben |
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October 16th, 2013, 01:41 PM | #14 |
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How does it run wide-open?
Set your idle mixture screws to high highest idle speed, then turn out 1/4. That should put you around 2 1/2 turns out usually. If wide-open isn't good, your carb (main jet) is partially plugged and needs to be removed and cleaned. |
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October 19th, 2013, 05:13 AM | #15 |
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Thanks for all the help.
I am removing the carbs and cleaning them (its going to be a wet and cold weekend) and I have all the screws removed and the boots going to the engine and the airbox loosened. I removed the screws for the airbox to give it some movement but I still can't back it up far enough to get the carbs out. Is it suppose to be this difficult or is there something I am missing? Thanks Ben |
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October 20th, 2013, 11:47 AM | #16 |
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well, I got it in. Everything is running 1000x better.
thanks again for all the suggestions |
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October 20th, 2013, 05:29 PM | #17 |
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Name: Jay
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October 20th, 2013, 09:38 PM | #18 |
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Well most everything inside the carb was clean but I sprayed out the jets with carb cleaner just to be sure. Otherwise I readjusted both of the mixture screws to 2.5 turns out from full lock, put some slightly less thick washers under the carb needles, re installed, and kaablamo! Low end power delivery used to be rough and hesitant, but now it is smooth and consistent.
I think I am still running a little rich because it takes a few seconds the tach needle to return to idle from a rev (that means its too rich, right?) and sometimes it will stick 1k to 1.5k rpm above idle. |
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October 20th, 2013, 10:41 PM | #19 | |
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Quote:
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October 21st, 2013, 06:56 AM | #20 | |
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Quote:
Check for leaks with carb cleaner around the manifolds. If that's fine, turn the idle mixture screw out another 1/4 and see if it gets better. |
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October 21st, 2013, 07:32 AM | #21 |
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It is too lean.
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Motofool .................................Never ride faster than your guardian angel can fly "Mankind is composed of two sorts of men — those who love and create, and those who hate and destroy. Love is the bond between men, the way to teach and the center of the world." - José Martí |
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October 21st, 2013, 07:43 AM | #22 |
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Name: Ben
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Ahh, thanks guys, you learn something new everyday
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October 21st, 2013, 07:44 AM | #23 |
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Oh okay so mine makes sense.
Sorry, OP, guess it's either down to the aforementioned vacuum leak or some other issue.
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October 21st, 2013, 07:47 AM | #24 |
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Name: Ben
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I am going to see what turning the needles a quarter turn out does. Now, I just need a really small flat head...
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October 21st, 2013, 07:51 AM | #25 |
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Good time to be an IT specialist, I have plenty of those laying around. Anyways, I hope you figure it out and if this is just what it needs.
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