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2005 Yamaha YFZ450
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Discussion Starter · #1 · (Edited)
Hey guys I have a 2005 yfz450 special edition I recently bought and it was standing for about 5 years I’m not sure if it was just standing without driving at all or someone drove it occasionally. It started and seemed to work and drive fine but the choke was working as it was reversed so when you pull on it the idle falls down and you push it in it raises but not too drastically but enough to where you can hear the idle change. It worked fine only when it is pushed in and has the higher idle otherwise it would be choppy and bog at low rpm. So I thought why not do a carb rebuild anyways since it’s been standing for a long time and it is not going to hurt anything. I flushed the gas from the fuel tank and put a new fuel petcock in and tore into the carb I even did the mid body gaskets and they were toasted blocking one of the small passages, everything went great and I thought it should be good, but no I put it back in and the choke seems to work the same reversed way although I had a moment were it started working great and the choke started working properly so when you pull the idle raises and you put it in it falls, but that was only for about a minute the idle adjustment screw is screwed all the way in as well and the adjustment really doesn’t do much. The bike has a drd exhaust, a k&n filter, and no lid from what I know. The jets were 45 for the pilot and 178 for the main so I just decided to clean them out really good and put them back I could clearly see through them before I put them back in it wasn’t like that before the cleaning. But it was wasn’t working good so I then removed it and even put the stock jet sizes back in and still wasn’t good. I also put a r&d fuel screw and have it 1 3/4 out. Sorry for the the long story but what I basically have currently is a cleaned out fuel tank, new petcock, cleaned out carburetor, 45 pilot and 178 main I also live in Washington just so you can get a reference of the sea level that I’m at, the fuel screw is 1 3/4 out, the needle is set to the 4th clip position, idle adjustment all the way in and it doesn’t do much, choke is working as it is reversed, very choppy and bogs when driving during low to mid rpms but pulls great up high, sometimes even dies, and it is hard to start occasionally. I also tried unscrewing the choke all the way and then the bike brings up the rpms really high. Any help will be appreciated it thanks and sorry for the super long paragraph that I probably wrote horribly.
 

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I would make sure your carb plate is not upsidedown and check to make sure your accelerator put is adjusted correctly, especially if you did the o ring/ziptie mod. The lack of the correct choke leads me to lean toward the carb plate being flipped.
 

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2005 Yamaha YFZ450
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Discussion Starter · #3 · (Edited)
I was actually making sure I don’t put the plate upside down and make sure the hole points down but I will check to make sure because who knows maybe I missed it. Also what is the accelerator put and how do you adjust it I’m guessing that’s the slack in the throttle cable and I adjust it with the two nuts on the carburetor, because I did do the zip tie mod so maybe I do need to adjust it correctly, thank you very much for the help.
 

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Here is a good video to adjust the accelerator pump

I have seen the zip mod also cause the throttle to hang due to slightly rubbing the inner cover and or behind the actuator spring.
 

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2005 Yamaha YFZ450
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Discussion Starter · #5 ·
Ok thank you I will go ahead and do that, and make sure nothing is rubbing, I’ll try it without the cover to make sure it doesn’t rub
 

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2005 Yamaha YFZ450
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Discussion Starter · #6 ·
The accelerator pump seemed to work well without adjustments I took a video of how it works but it doesn’t seem like I can put it in here, and the plate for the slide was in the correct way, is there anything else that the problem could be?
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Discussion Starter · #7 ·
Well I took of the plate off for the throttle linkage and look what I found, that does not look good. Could that effect anything?
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I would make sure the plate o ring is not swollen, check for vacuum leaks, and double check no hoses are plugged.
 

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If you are not in cold weather and you are jetting is close your choke is less critical. When it is cold the choke will slightly raise the idle until it is warm. After that, it will typically stumble with the choke engaged at idle.
 

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Discussion Starter · #11 ·
Ok sounds good thank you, I will check all of those things. It’s pretty warm right now Washingoton about 70F so maybe the choke is working but it is not needed. It seems to start without it pushed in that it is with it pulled out.
 

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Discussion Starter · #12 ·
I checked the o-ring it seems like it’s not swollen, and no critical vacuum leaks that I found, just one tube that goes to the air box wasn’t connected. But I tried adjusting everything and driving it for a little bit and it seems to work better now.
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Hopefully, you get it all sorted out. It's always harder to troubleshoot something you didn't build or put together yourself.
 

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Discussion Starter · #14 ·
Yeah thanks, I hope so as well. Yes that’s for sure I’m new to this type of equipment but once I start working on them and learn some things about them I should be pretty capable on fixing them. Also I noticed today that there is a decent size wet spot under the quad on the dirt where it was standing, and I looked under to see where it was leaking from and it looks like it’s leaking from from the carburetor bowl drain hose, do you think that it could be the the screw in the bowl that you open to drain the fuel, it is tight I tried it but can it still be bad and not holding in the fuel it is all stripped but I tried it with pliers and it’s tight. It seems weird to me why it is doing and I feel like it shouldn’t be leaking if it’s tight, or is it something internally in the carburetor that is making that leak out.
 

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I would check to see if the fuel is dumping out of an overflow tube. If it is, the float is stuck open or set too high.
 

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Discussion Starter · #16 ·
So I went ahead to check everything, replaced the drain screw, checked the float needle although it is new, the seat where the needle sits in, and the float height I found the point of the float just where it rests on the float needle and the little line was pretty much level with the body of the carburetor, or is it not set correctly, I will put in a picture to show it. So everything seemed fine to me, but it is still leaking.
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Discussion Starter · #17 ·
Actually I just looked at a how to video, should of done that before, but I didn’t put it back on so it doesn’t really matter I just connected the fuel line to test it, but it seems like it’s too high.
 

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The easiest way to do the float is with the carb on its side. When it is on the side just slightly move the float to touch the pintle but do not let it close the pintle. From there... measure from the flat seat of the carb to the tallest point of the bowl.

Here is a decent video, it way be the one you already have:
 

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Discussion Starter · #19 ·
Ok perfect thanks, I will do that, from the picture does it look like it could cause the leak?
 

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It's hard to tell from the pictures but all it takes is a few millimeters in the wrong direction for the float to never close.
 
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