Carb jets. Good place to start?

Doing a top end on my 2000 YZ250. When i removed the plug, I noticed that the bike had been running pretty rich. Pulled the carb to inspect. Float level is good. Pilot jet 45, main jet 168, power jet 80, pilot air screw 1.75 turns out. Do these numbers look reasonable? I dont want to put everything back together if I need to change something now.

Thanks!

Anyone?

Its hard to say, really.

If I were setting up MY bike, I would probably start with a 48 pilot. A 48 is usually close enough to work. As far as a main, I would start at 170-172. I am at a higher altitude than you are, but its probably cooler here, so that may even out. But again, thats for my bike...not yours.

Jetting advise is impossible to give, really, without knowing what your bike is doing wrong. We also dont know what ratio you are mixing your fuel at. In general, your jetting is lean. I would rather start rich, then lean it out.

Thanks for the advice. The manual calls for a pilot jet #50 and main jet #178. I bought the bike used and it has a FMF exhaust system and maybe an upgraded intake. Thi is my first bike but wouldnt i want LARGER than stock jets to allow more fuel to compensate the exhaust and intake upgrades? Where is a good place to buy the jets?

Thanks!

You should be able to get some jets at a yamaha dealer if there is one in your area. That's what i've done

Adjust the needle before you swap brass. Not a big deal to try different jets later. Tilt the carb. on the bike.

Depends on the mods done... FMF exhaust wont throw anythng off far enough to require jetting changes. If your just talking about a aftermarket reed valve ass. that probably wont throw numbers off much either. When I got my 08 new I put a DEP exhaust and boyeson reeds on my 250 and I ended up leaner to find ideal jetting. When I had port work and started using race fuel is when I actually needed jetting changes to improve performance.

Thanks for the advice. The manual calls for a pilot jet #50 and main jet #178. I bought the bike used and it has a FMF exhaust system and maybe an upgraded intake. Thi is my first bike but wouldnt i want LARGER than stock jets to allow more fuel to compensate the exhaust and intake upgrades? Where is a good place to buy the jets?

Thanks!

This can be argued either way. Logic says you need more fuel, btu did the mods improve efficiency, and fuel signal so much, that so much more air flows through and it automatically picks up more fuel as this is happening. So, its a crap shoot any way you look at it.

Like i said, I'm new at this so i didn't check the needle clip position :thumbsup:. The manual calls for 2nd notch, ill adjust and see what it does. Thanks for the help!

Needle clip was in 1st notch. Moved the clip to the 2nd notch per the manual and finished the topend rebuild. When i cranked it up, it "bogs" or "misses" (not spark related) when the throttle reaches 3/4 to full throttle. It didn't do this before i changed the clip position so logic tells me to put it back to the 1st notch. Im still confused on why it is running rich when the carb is setup this way. Should i try the 3rd notch instead of moving it back to the 1st notch? Or just not worry about it since it ran fine and im not too concerned with all-out performance? I am running 32:1 mixture. Should i try 30:1?

Thanks

Edited by JFoVStar650

bump.

The mixture wont change the bad jetting, fuel mixture is not where your problem lies and is commonly thought of a a cure. Moving the clip down another position will lean the jetting out between 1/4 and 3/4 throttle. May or may not fix your issue. I suggest dropping the main one step before going any leaner on the needle.

Edited by ftball90

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