05 yz450f wont idle... must run by friday!

So i left the bike sitting for too long with gas in it. Bike would only run with the choke on. removed the carb, cleaned all passages/needles/jets with carb cleaner and compressed air. Before i removed the pilot screw i turned it in 2.75 turns till it stopped so i could set it back to stock after cleaning. bike will start on choke and run, but dies as soon as the choke is turned off. bike will stay running if i keep the revs up and turn choke off, but dies when i let off. with the choke on the idle adj makes no difference. My GF is taking me on a secret trip this weekend that involves my bike so i gotta be running by friday. Please help! :smirk:

I know you will say that you already cleaned it, but the pilot jet is wholly or partially blocked with dried varnish. A piece of fine wire or a #80 drill inserted shank first may be needed to dislodge the clog. Or, you can replace the jet.

I'll never claim to be a pro with carbs... My expertise is automotive and not including carbs. I will pull the carb again and do as you say. I appreciate any help i can get. Thanks and i'll respond with results either way.

Thing is that the pilot in your carb has a metering orifice of around .015". A .002" film dried on it makes it much smaller than it should be.

Were you able to actually see carb cleaner pass through the carb body into the venturi when the carb was off? I usually secure the slide in WOT position with a zip tie while doing carb cleans. This way I can verify that the float chamber area is in communication with the venturi. Eliminates guesswork.

Also, make SURE the o-ring and small washer are present and accounted for on the fuel screw if the fuel screw is completely removed. Different symptoms would manifest than what you originally described, but the absence of the o-ring will cause a new, different problem.

just buy a new pilot jet its the best way

I ordered a new pilot jet and also the 2 washers for the pilot screw because i don't remember ever seeing them. That might be why i turned the pilot screw in 2.75, but when i reinstalled it and turned it out 2.75 there felt like there was no spring pressure. parts will be in tomorrow. Hope this works. in the meantime i'll pull the carb again and double check the passages and other jets again. i'll also reference the exploded diagram and make sure im not missing any other tiny washers or o rings like i believe i am on the pilot screw. thanks for the help everyone and i'll post results.

The pilot screw O-ring likes to stick up in the bore, and will sometimes also hold the washer there. Might have a look at that.

From now on get yourself some quikshot se from amsoil and save yourself the headache off gummed up carb. It works great and clean up the carb while you ride.

So... I installed the new pilot jet, replaced my missing o-ring and washer on the pilot screw, and installed an MSR pilot screw so i can avoid the pain-in-the-ass of adjusting the OE screw on the bike. It starts and idles on and off the choke and seems to be fixed. I am noticing that the snap-throttle bog is worse than I remember. Any advice on that?

With the pilot adjusted correctly, a warmed up engine should be capable of tolerating a fairly quick opening of the throttle, but it is unreasonable to expect that it will ever be able to handle an instant whack from idle to WOT unless the accelerator pump is so heavily upgraded as to cause other performance problems. The correct way is to "roll" the throttle, a technique that simply involves starting the throttle open a bit more gradually, and opening it faster as the the engine responds to it. When done correctly, whole twist takes almost a full second, and the engine sounds as if it responded instantaneously. Once you learn this, you'll do it without a thought, and your bog troubles will mostly go away.

But if it will not do that, and the pilot is not too lean, first check the accel pump timing per the manual. If there is still a problem, then proceed with the "BK Mod":


thanks for the info! it does respond nicely to a roll-on approach. I'm going to play with the pilot adjustment a little more before I mess with any other mods. We'll see how it rides this weekend. Also a jetting question. My carb has all stock jets and I ride pretty much at sea level. I'm in central florida... what's elevation? lol! is the stock jet setup fine. the bike is stock too... no pipe or anything.

The thing always to question is whether it really bogs in some impractical way when you actually ride the bike. Then, if it turns out that it does, consider whether it's really the bike messing up, or do you have a bad habit to correct? After that you have to ask whether the "fix" will cure one problem without causing another. Once you have all that down, you can decide the right way to go with it.

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