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09 backfiring and won't idle.

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Ok, I have read a lot of posts on hot start issues. I hope this is my issue. Here's the deal. 09 250 f bought new. Put an hour meter on it when I bought it. It has 51 hours. Change oil every ride. Change oil filter every two times. Changed at least ten times maybe 11. Air filter is cleaned and oiled every ride. Hot start lever seems to work fine. When running, I can pull the hot start lever and hear the difference in the engine.

Here's the problems. When cold, starts right up with the choke. I let it run a couple minutes and I am good to go. When I let off the throttle, it back fires constantly. All day long. When it's hot, I can start it without pulling the hot start lever by just slowly kicking it over. Almost every time. I also have to adjust the idle through out the day. Sometimes up and sometimes down. When I let off the throttle back to idle, it seems like it takes a second to idle down. Not just the quick snap back to idle. It idles real rough and sounds like it is skipping. It has all the power when I get on it that it has always had. I use 93 gas and it is fresh. I've had this issue the last two times I've ridden it. I put 54 miles on it Friday and 47 on Saturday up in WV at Hatfield McCoy. I have not checked valve clearence yet. I will sometime this week. The last issue is a sound I hear. It sounds kind of like a turbine engine sucking air but only some times for a second at a time. I thought it might be a crack in the exhaust pipe but don't see a thing. Might not be a related issue. This sound started a while back after getting on it going up a real rocky trail. The plan. Take bike apart and check out the hot start system. Check valve shims for correct gap. Check compression. What should the compression be? Don't want to pull the head off unless you think I should. Won't the compression test tell me if I have a burned valve? Any help is appreciated.

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Could be the copper crush gasket between head and header. Maybe just not tight enough. Check easy stuff first.

Make sure the coil is firmly pushed down on spark plug.

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Stock pilot jet. ? Haven't checked the coil or plug wire. Do the plugs foul on a 4 stroke? I haven't pulled the plug to check its color yet. Pilot jet might be plugged. It seems the issues are idle issues or when the throttle is closed. Hope you are right on the copper squish gasket.

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The stock pilot jet (#40) is always too lean.

A #42 is money, maybe even a #45 in colder temps. Also check fuel screw setting.

However, if the bike developed this problem suddenly, after 50 hours of use, the problem is hardly in the jetting. Well maybe if you count clogging and dirt as jetting.

Plugs usually will not foul, but it can happen. In that case the bike will most likely be hard to start. I run plugs for 50 hours, I change them with the piston.

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Update. Valves were perfect in spec. Replaced the spark plug, tightened the pipe bolts to the head, put in the 42 pilot.....runs like a champ and no backfire. Thanks for the advice.

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Update. Valves were perfect in spec. Replaced the spark plug, tightened the pipe bolts to the head, put in the 42 pilot.....runs like a champ and no backfire. Thanks for the advice.

Great to hear:thumbsup:

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