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2004 YZ250F lean backfire's


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I have a 2004 YZ250F that i just bought from my cousin. Long list of maintaince records and whatnot. Just had it at a shop and he got it back and it ran great til he let it sit for 3 months. Initially it wouldn't run unless the choke was on, it also was leaking fuel so I replaced it and it didnt change much. I cleaned the carb and then it would run off of choke but would pop on quick throttle openings and pop out the exhaust on decel. Classic lean condition right? I messed with fuel screws and cleaned the carb again and lowered the clip on the needle, put fresh gas in it and it ran better yet. less popping on quick throttle openings and significantly less popping on decel. The bike had a slight revhang while off choke that went away yesterday after the last cleaning however it still has a revhang while on choke trying to ride it. While on choke the bike runs perfect, no bog, no hesitation, no popping just a slight rev hang while returning to idle.

Bike is 100% stock and has a 100% stock carb.

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What's all the talk about the slide plate being upside down?

Are they talking about the actual slide itself being upside down??

I'm going to pull this carb out again and see what I get and do the o-ring mod while im there and see what happens.

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They refer to the vacuum release plate. Did you remove the slide from the carb? Typical symptom of the upside down plate are extremely high idle.

Oring mod ony affect bogging.

I strongly reccomend you do one thing at a time or else you wll never kjnpw what did what (for better or for worse).

Think for a minute. You got the bike back from the shop and it was great. Not it is not. What changed? Nothing other than the fuel aged. You more or less cleaned the carb and saw some improvement. That means you are probably on the right track. Pilot jets are very difficult to get perfectly clean. For all the efforts you are going through, spending the five bucks should not be a big deal. After you install the new jet, carefully adjust the fuel screw once the bike is fully heated.

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I finally got the thing to run right and idle right and got rid of most all of the popping on decel and all of it while on throttle. A fresh clean pilot did that with some fuel screw tweaks.

Can you show me a picture of this slide plate when its right side up and upside down so I know what to look for in the future, i also have a CRF450 that wont run right.

I still have a bad bog on throttle, I tried to adjust the AP but not sure what im doing here. I backed off the screw a little thinking maybe the squirt is hitting the slide but it made it worse I think.

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Again, only fix one thing at a time. Forget the bog for now.

The vacuum release plate has one end that is squre, it goes down, the other end up.

To deal with a bog, once the rest of the jetting is exactly corrrect and the bike runs perfect except for the bog, what you want to do is install a smaller leak jet, often between a #40 and #60 - #40 is the most popular. The, ride the bike and tweak the AP timing screw, 1/2 increments CCW. Keep good notes of exactly how much you turned it as resetting it to stock is a real pain.Ususally, less than 2 turns is needed, often just 1/2 tuun does it.

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i only put 93 in it. I spoke to the previous owner and the bog was never there before. Im going to tinker with this AP adjustment a lil bit and see what I get out of it. Obviously backing off the screw makes the timing later and screwing it in makes it quicker. I was thinking maybe the fuel was hitting the slide but backing off made the condition worse. I pulled the plug and its actually new and is white on the porcelin and has a dark black electrode protruding but it's dry not a wet carbon like overly fueled. I think this plug is still too virgin to give any real tuning details just yet

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