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Could my carb be bored out?

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I had my bike apart yesterday and figured that I would see what jets are in it. My main is 200 and the pilot is 50. Is that a big main jet for a 2005 yz250? The bike isn't running like it is super rich though, it may even be lean. The previous owner didn't say it was bored out.

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IMO that depends on how you ride. When I started out I went with 172 on the main, with the Vortex CDI I had to go way higher. Vortex among other things advances your timing.

My riding style was way different too, I got away with about 50 hours on a tire. Now I cut that down to 30 because the knobbies fly off at that time. I also had to adjust piston change intervals from 50 hours to 40. Now the piston looks kind of reasonable before it came out almost all black.

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The previous owner ran 32:1 and so do I. Someone told me that a previous owner could have had the carb bored out and that is why the main jet is so big.

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A worn out top end will require much richer settings. Pull the pipe and look and the rings/piston.

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I'd try a smaller one before a larger. Why do you think it's lean now?

Is the needle stock? A slower tapered needle like a B or even C from Sudco would need a bigger main. Not a 200 though.

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Ill look at the needle tomorrow, the bike doesn't bog or anything so I don't think a leaner one would help and winter is coming up to. Would a leaner pilot help the bottom end?

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Does the bike sputter or bog?

Sputter = rich

Bog = Lean

I have never heard of anyone running anything close to 200 for the main jet on a yz250. I run a 175 and it's still a bit rich.

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Yea, I'm still thinking if it's running well with a 200 main than either it's bored out or the air bleeds have been modified.

I've run as low as 165 at higher elevations, typically run a 172 or 175. Last year I threw in a 185 for a 20 degree day ride, figured it'd be a bit rich but OK since I'd be on the throttle a lot to try and get through the snow. Way fat, smokey, blubberly, had to "clear it out" every time I got off the pipe for more than 2 seconds, overall just ran terrible. I imagine with a 200 main my bike would make it about 5 seconds on the hammer before fouling out....

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Ill measure the carb, the bike ran fine like this with the stock pipe and PC Platinum. I think I'll throw richer jets in it either way because it's starting to get in the 50's- 40's now and I don't wanna be running lean.

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I have rb's bored carb on my 300 and I run 170 48 in summer at 800 to 1000 ft. Ive ran down to a 165 45 on the right day and still not blown the bike up. 200 to me seems huge are you shure you dont have an air leak leaning things out. But I have a stock bore and carb 250 also. How do you check if 200 is rich. Are you cutting plugs?

I run 40:1 that might be why were so far off. Have you ever retimed the bike. If you havnt I bet the timing is way advanced and thats why you think your lean.. My 05 was set a .009 book calls for .007 but ive found .005 is the sweet spot for me. If you dont run fresh 92 or greater with the bike at .009 you will think its lean all the time. If you retard the timing slightly the bike will be more torerant to bad fuels and leaner jetting. Have you checked your reeds also. I noticed once when my reeds were chipped the bike started wanting fatter jets.

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The previous owner didn't do anything to the bike and put a good amount of hours on it, everything done to it was done by the owner before him. If the carb isn't bored then maybe its the timing that's off. Ill measure the carb tonight.

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Ill measure the carb, the bike ran fine like this with the stock pipe and PC Platinum. I think I'll throw richer jets in it either way because it's starting to get in the 50's- 40's now and I don't wanna be running lean.

Mark the grip then run all throttle postions(1/16,1/8/3/16,1/4,1/2,3/4 and WOT) for 10 seconds then chop the throttle to idle. If the idle hangs then that position is lean. If not it's not lean. If you get a "bong" on the chopped throttle then richen the airscrew. You should have light sputter at steady throttle and very little to no visable smoke looking behind you. If the rpm wants to climb or bike surges at steady throttle it is lean.

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