YZ250F carb questions

[yzernie]

Most of you know I just picked up an 03 YZ250F that doesn't even have the paint worn off the frame rails. I'm having a problem getting it to run clean on the bottom end and top end. I have added the YZ filter cage and the Big Gun Race Series pipe. I run 50/50 VP C12 and premium pump gas. It RIPS in the mid range.

Bottom end:
The dreaded bog and alot of snapping and backfiring on decel.

I'm thinking of taking the carb off, cleaning it because the bike sat for a few months before I got it, checking the ac pump squirt duration and possibly rejetting richer....am I in the ball park??


Top end:
Doesn't seem to want to rev out like Russ's 04. Hoping the cleaning will help but I will try richer jetting when I put it back together....am I in the ball park??


I believe I have heard sometime in the past that the 03 ignitions could be a problem?? True/False??

Thanks in advance, Ernie

[Woody_393]

Not sure on the ignition, but everything else sounds spot on to me (what you are going to try).

After cleaning I'd start with turning the fuel screw out in quarter turn increments

Go one size larger main.

The jetting is really no different then your YZ250, and I know you are good at that. So yeah you are in the ball park.

Any idea what Russ's jetting specs are? I don't think the carb changed from '03 to '04, so an easy way may be to see what his has vs what yours does.

[yzernie]

Thanks Woody. Russ's jetting is stock....er....it is what came in the bike!!! I've always had a YZ be right on the money as far as factory jet size.

The previous owner said he never changed the jetting so I'm thinking it may be a tad gunked up (is that a word??) from sitting for a while.

Anxious to tear into it.

[Woody_393]

I just meant the actual sizes since it's possible the jetting was changed. I know on the CRF from '02 to '03 it did change, though the carb was the same.

So if the main you have is different then his, you could just make them identical etc.

[yzernie]

Good point on the year to year changes. Didn't even think about that. I'll have to check it out.

[Woody_393]

Just might make it easier then guessing what size to go with.

I'd probably go the next size larger on the main anyway, based on what you stated, as well as a couple of turn (1/4 turn at a time) on the fuel screw. If you get above 2 1/4 - 3 turns out (above 2.5 I like to go to the next larger pilot), you should be fine.

[Florida 393]

Ernie,
There is a neophrene gasket on the bell that mounts to the back side of the carburetor. The bell has three screws holding it in place . the gasket can get sucket out of its groove and cause an air leak that will give you some of the same symptoms.

I would also do a through cleaning of the carburetor. Do not take the yellow painted screws out to split the carburetor in half. These are the screws of death. I would have me three steps leaner of the main and pilot jest to work with. Also, take a multimeter and go through the throttle position sensor readings and the readings for the black box while running.

Good luck and keep us informed.

Bill

[AndrewPA]

Aha! THAT is why it was so cheap!

Just kidding Ernie, because I am still jealous!

[yzernie]

Bill,
Good info, Thank You!!

Andrew,
I'll get it running really good then sell it to you....for a profit of course!!!

[Faded]

Originally posted by Woody_CRF
So if the main you have is different then his, you could just make them identical etc.

Ernie,

Be sure to compare needles as well (I know you know this ) because variances in straight section, taper angle and length can affect jetting from 1/8 throttle all the way up to WOT. It's not uncommon for manufacturers to spec different needles for every model year bike.

Also, I know you've experimented with race fuel (C12 if I recall right) and that will normally have a different jetting spec compared to pump (generally leaner jetting is required).

Good luck, let us know how it turns out.

[Woody_393]

yeah, what faded said... If you can trust him anyway

[rockstar9]

I have a 1994 yz250 that hasnt been run in 9 months it sat around and i got it and rode it around and its running really rich and its kind of bogging out when i crack into it. also if i run it for 5 to 10 min it will cut off and wont start like its fluided. can anyone help me with this?

[Woody_393]

Rockstar9, this thread is 5 years old, I suggest starting your own new thread. You'll get some help there.

[lucky]

rofl!