Backfire thru exhaust - Kawasaki ATV Forum
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post #1 of 17 Old 02-24-2011, 12:35 PM Thread Starter
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Backfire thru exhaust

Just picked up the 06 bf650i today. Had some hard starting and idleing problems when i picked it up. Bike ran strong when we got it going but backfired a lot on deceleration and when revved in neutral. Bike has 430 miles and about 44hrs. It belonged to the sellers daughter and she just quit riding it. Put some seafoam in the gas and ran a few miles, but dont think it helped. Its about 25degrees outside and i froze before i could give it a good run. The bike aint paid for yet, and can give it back. All opinions and concerns are welcomed. By the way, thanks for the tire and wheel advice Al
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post #2 of 17 Old 02-24-2011, 01:07 PM
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I'd start by checking valve clearances and run about a tank of fresh fuel. I've owned mine since new, and it always acts funny on cold days until it warms up real good.

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post #3 of 17 Old 02-24-2011, 01:53 PM
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My two Bf 750 machines have always backfired on deaccel. Hard start and backfire is always valve adjust.

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post #4 of 17 Old 02-24-2011, 02:36 PM
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Sounds like a good carb cleaning wouldnt hurt before any valve adjusting. Doesnt have enough miles on it to need any of that. Especially if its been sitting up. If your asking for advise on to buy it or not. With so few miles I wouldnt hesitate depending on the condition of the bike. Something you will have to determine. Clean the carbs and see what happens. Good Luck..

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post #5 of 17 Old 02-24-2011, 04:14 PM Thread Starter
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Gonna start with the carbs. If its the valves, aint sure if i will do that since the bike aint really mine yet. Thanks for the info. Al
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post #6 of 17 Old 02-25-2011, 08:42 PM
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dude trust me its not your valves, some people just want to jump to the most extreem thing first, most of my new young mecanics would act like that yrs ago when I was a shop forman, a little knowledge is a dangerious thing, as a good mecanic should do is allways start with the easy fix first then move on to the next harder, your running lean and in o5 or 06 they started to plug the idle adjustment screw hole and didnt turn them out much over 1.5 to 2 full turns out for epa reasions, but we are getting ahead of our selfs, first take a can of carb cleaner, and spray it by the carbs while its running if it picks up rpms then you have an air leak prob in a carb boot, if no raise in rpm then pull your air cleaner cover and make sure the rubber seal is not broken or out of place and that the cover fits tight, but seeing that the bike is new to you and it sounds like it sat for a while you will prob have to open up the carbs and clean them, (gotta love the corn gas) and pull the seals they put over the idle adjustment screws and turn them in till closed and then turn them out to 2.5 full turns out, also at that time you might want to get a no4 washer and place it under the head of the needles that will raise your needle a bit and make it run a bit richer
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post #7 of 17 Old 02-25-2011, 09:10 PM
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Agree ^ prob running lean due to the cold weather.....cold air requires more fuel but check and make sure carbs are clean and that you have no air leaks around intake or exhaust first.


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post #8 of 17 Old 02-27-2011, 06:02 AM Thread Starter
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Thanks for the info, guys. Agree on the lean condition. Cleaned carbs as best i could without rippin and tearin. Still would not idle after playing with enrichener and throttle for about 15 min. Could get it to idle with adjustment knob all the way turned up and enrichener open some, although a bit high. Cant really start drillin out plugs and pullin carbs apart, because i only have the bike for a test before possibly buying. Had to do that to an 83 HD sportster years ago and it did the trick. Kind of in a delemma now and not sure about buying the bike not running right. Thanks again for your input Al
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post #9 of 17 Old 02-27-2011, 08:55 AM
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Albie...I agree with the advice given as well, and believe that you won't be able to correct the problem without removing the carbs and more specifically cleaning the pilot jets. The pilots have such a fine passage way for the fuel to flow through that it only takes a grain of sand or film of residue to clog them completely. When that happens, the quad won't start or idle very well because the pilots allow the necessary fuel flow during the low speed circuit and also continue to provide fuel when you back off the throttle.
If it were me I would do the following before purchasing it..
1) Confirm it's never been sunk or injested water. If it has, walk away or reflect a rebuild including crank, rods etc in your offer/price.
2) Remove the front and rear differential fill caps to ensure the lube is clean, not contaminated or watered down like chocolate milk.
3) Negotiate a better price because of the required work.
4) Purchase it and do the following..
5) Remove all of the existing fuel from tank, carbs etc.
6) Remove the carbs
7) Remove the pilot screw adjustment caps/plugs by drilling a small hole through the cap and prying the aluminum plug out. Be careful not to drill any deeper than just through the thin plug or you'll damage the slotted head of the pilot adjustment screw.
8) Remove the float bowls and ensure that everything is spotless, especially the pilots. You'll need to remove the pilots and hold them up to the light in order to verify the passage is clear. I would suggest you do the same with the main jets. The mains are less likely to be clogged because the holes are significantly larger than the passage way of the pilots.
9) Clean the choke plungers while you have everything apart because they've been known to stick which will have it's own set of issues, e.g.too rich or to lean.
10) Shim the needles and adjust the pilot adjustment screws as per reelnative's advice, e.g.screw them in until they seat and then back them out about 2 1/4 to 2 1/2 turns.
11) If it were me, I would inspect the valve clearance while the carbs off, but only do this if you're confident with the process because it's fairly unlikely that you'll need to actually adjust them. If you're not familiar with the process and end up adjusting them out of spec you'll have bigger problems.
12) Put it all back together, fill it with fresh gas and go have some fun: )

Hope this helps.

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post #10 of 17 Old 02-27-2011, 10:49 AM
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sorry guys to disagree just CHECK FOR AIR LEAKS FIRST look on the intake manifold to cyclender head then check jets it may need some re jetting but that dosent make it idle fast like an air leak. it's probably a simple fix maybe thats why the young lady did'nt like ridding it you fix it buy it for a good price and your the WINNER.

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