07 YZ250F carb question

[Frank ZX]

I have posted in the Carb jetting data base over a week ago with no responce so I will try here. I have a 2007 YZ250F that is bone stock. It does have a K&N air filter which is getting replaced soon. I hate K&N in dirt bikes.

The problem is the bike pops all the time and takes 30 minutes to warm up.

I can't afford a JD jet kit right now but I do want to correct the problem.

jetsrus.com sells jets dirt cheap. Can anyone tell me where I should start jetting. Can I get away with just a bigger pilot jet? I am at 1000ft above sea level. Please help.

Thanks

[William1]

You start jetting setup with stock jetting. You select the pilt and fuel screw for a good idle and leave it alone. Then you do the main jet, then you work with the needle straigt diameter and finally with the needle taper, length and clip position.

Popping is a fact of life with a race bike being trail ridden.

Fuel Screw/Pilot Jet

Fuel screw settings in the 'book' are recommended starting points. Every bike is different, as is the temp and altitude. Set the screw according to this method. Do it with the bike fully heated up.

Gently turn the screw all the way in. Now back it out two turns. Start the bike and fully warm it up, go for a 10 minute ride. Set the idle to speed to 1,500~1,800 RPM as best you can (I know, without a tach this is tough, just set it to were it idles relatively smoothly). Once warmed, slow the idle to the lowest possible speed.

*** When turning the fuel screw, keep an accurate 'count' of the amount you are turning it and record it in case you have to reset it for some reason. Makes life easier when you can just set it from notes Vs. going through the procedure again.***

Turn the screw in until the idle becomes rough or the bike stalls.

if it stalled, open the screw about 1/4 more turn. Restart it and slowly screw it in till you can just perceive a change.

If the screw can be turned all the way in and the bike still idles perfectly and does not stall, then you need to go down a size in pilot jet.

Now very slowly, open the fuel screw till the idle is smooth. Blip the throttle, let the bike return to an idle, wait say ten seconds. Confirm it is the same smooth idle.

If the screw has to be opened more than 3 turns to get a smooth idle, you need to go up a size in pilot jet.

If you find it does not stall with the larger jet but has to be open more than three turns with the smaller pilot jet, put the larger one in and set the fuel screw at 1/2 turn.

If the idle speed increased, adjust the idle speed knob to return the bike to a real slow idle speed. You must then re-visit the fuel screw. Keep doing this till the fuel screw is opened just enough to provide a nice steady idle at the lowest possible RPM. Once this is done, increase the idle speed to the normal one for your bike, typically about 1,800 rpm, but go by the spec in your manual.

[Frank ZX]

Thanks William1, I try this now.

[Frank ZX]

Okay, I just came from the garage, and the pipe melted my air box! It also puked coolant onto the garage floor.

I comfirmed the pilot screw was 2 turns out. I started the bike and began letting it warm up. I had to hold the choke half way out for it to even idle at all. At full choke it idled too fast. While idling I turned the idle screw in which made idling worst.

It seems to me it is too lean. It has the stock 40 pilot jet according to the previous owner. Should I order a 42 and 45?

I do understand every bike is different. This is the 2nd 2007 YZ250F I have owned. I sold the first one to my buddie. That bike was also stock and experenced the same problems. He took my old YZ to the bike shop and they changed one jet and now the bike runs perfect. Problem is he don't know which jet or size.

[William1]

It sounds like to me you did not follow the directions I gave. First, letting the bike warm up by idling is not a good idea. You need to ride it to honestly heat it up. Then follow the procedure I outlined. The procedure will categorically tell you if the pilot jet is sized wrong. It will also get your fuel screw set perfectly. With a hot bike, iot takes less than a minute to do.

Read the procedure a few times to ensure you fully understand it.

[Frank ZX]

Thanks again William1. I just got off the phone with my Buddie that bought my old YZF and he scolded me for letting it idle so long.

Your right, I didn't follow your exact instructions. My bad, and now I have a slightly costly mistake.lol

My friend told me the bike shop installed a 45 pilot jet and that cured his problems.

I can't touch the hot engine once it gets warmed up to turn the air screw. I'm going to have to buy a 90 degree screw driver(gear driven).

I can almost guarantee the fuel screw will be 3 turns out to make it run right. I will try it again once it cools off some.

[William1]

If you find, that with a NEW (not just 'cleaned') 40 pilot, you need to be at 3 turns, then yes, the next size should be tried, a 42.

If you go too large, hot starts will be a problem as well as getting a good setting on the fuel screw. They do not like to be less than a turn open.

Instead of buying that tool (which is handy, I have a Motion Pro one) why not get an extended fuel screw? Do not buy an alloy one, get a brass or stainless steel one (Kientech, Kouba, James Dean, Scotts, Merge Racing - All great screws)

[Ian O'Brien]

Yeah I have a 2007 YZ250F I just got and the guy did a "carb rebuild" and said it needs jet work because it wouldn't idle.... got the bike home went on YouTube and found that the fuel screw wasn't even in the carb! Wtf! I went and bought one for 20$ and screwed it in and the thing idles now. But I think there is more than that wrong cause when I blip the throttle it bogs then revs up. And when I'm riding around it pauses and bogs a little bit before reving up. Is this the pilot screw or somthing else? Getting fed up with it

[ohiodrz400sm]

Yeah I have a 2007 YZ250F I just got and the guy did a "carb rebuild" and said it needs jet work because it wouldn't idle.... got the bike home went on YouTube and found that the fuel screw wasn't even in the carb! Wtf! I went and bought one for 20$ and screwed it in and the thing idles now. But I think there is more than that wrong cause when I blip the throttle it bogs then revs up. And when I'm riding around it pauses and bogs a little bit before reving up. Is this the pilot screw or somthing else? Getting fed up with it

Make sure the components to the accelerator pump are in good shape. Also check the squirt timing, research the recommended leak jet size(MX Action tests are the 1st place I would look) and do the "o-ring mod" .

[MatthewMCRepair]

Copy this jetting exactly:

https://www.howtomotorcyclerepair.com/jeta4stroke/

 

Also, how to adjust AP timing:

 

 

Fuel screw tuning:

 

 

[BTD123]

Use Matthews recipe. It fixed mine.