05 YZ250F Only Runs on Choke

Roach
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OK US
3/8/2016 8:35am Edited Date/Time 3/21/2016 7:22pm
Hi All,

I just purchased an 05 YZ250F from an acquaintance. I've been without a bike for over 6 years, and this is my first 4 stroke. He's had this bike since 09, and it has pretty much just sat in his garage since then. When I test drove it, it would only idle when the choke was on, and I ran it up and down the street with the choke on. It ran great. Pulled hard. But as soon as I turn the choke off, it backfires and dies. So here's what I did when I got it home:

Pulled the carb and cleaned the jets with carb cleaner and an air compressor.

I put it all back together and put fresh new gas it in, and fired it up. It is still giving me the same issue. It'll run and idle on choke, but just backfires and dies as soon as I take the choke off.

Any ideas as to what I should do next?
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Dtat720
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Flowood, MS US
3/8/2016 8:42am
Pilot jet is clogged. Air alone wont clean it out. Have to put a pin or wite in it to clean it out. If it ran any ethanol gas, it is gummed up and cleaner and air doesnt get the gum out
Roach
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3/8/2016 9:21am
Dtat720 wrote:
Pilot jet is clogged. Air alone wont clean it out. Have to put a pin or wite in it to clean it out. If it ran...
Pilot jet is clogged. Air alone wont clean it out. Have to put a pin or wite in it to clean it out. If it ran any ethanol gas, it is gummed up and cleaner and air doesnt get the gum out
Would a pin or wire not scratch it up too bad?
OldnBroken
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Kamloops CA
3/8/2016 9:45am
Might check the hot-start plunger as well. If it is letting air by-pass it could cause this issue.
Dtat720
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3/8/2016 10:01am
Pin or wire wont scratch it, jet cleaning kits are different sized wires you poke through the holes

The Shop

Paw Paw 271
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3/8/2016 10:28am
If the bike set that long...I would just replace the pilot jet. Clean the starter jet and the main jet. I would also replace the fuel screw o-ring and then set the fuel screw. The hot start plunger can also leak and cause the lean condition as was mentioned.

Paw Paw
Roach
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3/8/2016 11:11am
If the bike set that long...I would just replace the pilot jet. Clean the starter jet and the main jet. I would also replace the fuel...
If the bike set that long...I would just replace the pilot jet. Clean the starter jet and the main jet. I would also replace the fuel screw o-ring and then set the fuel screw. The hot start plunger can also leak and cause the lean condition as was mentioned.

Paw Paw
I think my next step is to just buy a jet kit like you alluded to. The hot start plunger doesn't want to thread in and hold tight. I didn't even think of this causing my issue. Would I need to replace the whole part to get this fixed, or can I use like a silicone style sealant to hold it on?
Paw Paw 271
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3/8/2016 1:45pm
Replace the hot start plunger. If it leaks you will run very lean.
You don't need a "jetting kit", just a new pilot jet and a fuel screw o-ring. You may also want to look at the accelerator pump diaphragm as they leak over time.

Paw Paw
DuroTools
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Middletown, CT US
3/9/2016 7:08pm
The plastic hot start nut threads always strip, I just put a blue anodized aluminum one on my dads YZ250F, looks good and fixed a similar issue. I think it was like 10 bucks on eBay from ADA racing, here's the link in case you need it
[url=http://www.ebay.com/itm/Keihin-FCR-Carb-Billet-BLUE-Hot-Start-Nut-Honda…Tongue 8kAAOSwGWNUXAAJ&vxp=mtr]
Roach
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3/18/2016 4:38pm
Ok, so I bought the carb rebuild kit for good measure instead of just the pilot jet and fuel screw o-ring. I also bought one of the anodized aluminum hot start nuts (thanks DuroTools!).

Now I'm going to need to order an accelerator pump diaphragm, this one is just falling apart. BUT, I also need another part that I can't find on the carburetor diagram. I've circled it in blue below:



Can anyone help me identify this part so I can buy a new one?

3/18/2016 7:11pm
That is the accelerator pump nozzle. If im not mistaken, it is not replaceable as it is pressed into the carb body. I could be wrong because I have never had a reason to remove one.

Why do you want to replace it? Is it clogged? You should be able to clear it with carb cleaner and compressed air. If it is clogged with pieces of the pump diaphragm it might take some time, but you should be able to clear it.
Roach
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3/18/2016 8:31pm
That is the accelerator pump nozzle. If im not mistaken, it is not replaceable as it is pressed into the carb body. I could be wrong...
That is the accelerator pump nozzle. If im not mistaken, it is not replaceable as it is pressed into the carb body. I could be wrong because I have never had a reason to remove one.

Why do you want to replace it? Is it clogged? You should be able to clear it with carb cleaner and compressed air. If it is clogged with pieces of the pump diaphragm it might take some time, but you should be able to clear it.
Well.. embarrassingly enough, I thought this was one of the jets that I needed to replace, so I removed it. It broke in half during the removal.
Paw Paw 271
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3/19/2016 10:12am
Now you will need a carb body.

Paw Paw
jaredtebo17
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Raymore, MO US
Fantasy
1813th
3/21/2016 7:22pm
I had experience with that same issue. Bought a brand new 2006 YZ450F and it had the same issue, put the choke in and backfire and get wicked hot real fast. Took it back, they traded it for another brand new bike. Took it home, had the same thing. Finally took it to a different shop, the hot start cable was zip tied too tight to the frame. The hot start was always pulled. Choke on it ran ok. I think your issue is all in the hot start.

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