Smaller pilot jet?

I decided to swap the stock 45 pilot jet in my 2009 YZ to a #42, because I saw it recommended somewhere and my bike would always start easier when using hot start (even with the engine cold). So now, after re-adjusting the fuel screw, starting the bike is how it should be (using choke and hot start only when necessary). But for the first time ever, there is sometimes a slight bog or hesitation (1/8-1/2 throttle openings) when riding.


I'm not really a jetting expert, but I don't think it has anything to do with the leak jet (bike has a R&D power pump AP cover set to #60 leak jet). I feel like the bike is running lean now (mid-throttle openings), and I should raise the needle a clip or 2, and probably turn the fuel screw out more. I just want to make sure that this really is what I should do before I do it...and how many clips should I raise the needle?


My current jetting is 42 pilot, 165 main, NFPP needle 4th clip. Full DRD exhaust, riding in SoCal deserts.

#60 is bigger than the original LJ (#55) by a considerable amount.  That makes the pump discharge weaker, not stronger (leaner, not richer).  The first thing I would try is returning it to #55 and go from there.

I adjusted the leak jet to #55 and replaced the spark plug (maintenance). The bog is gone, but now the bike usually runs a little rough/sputters at smaller throttle openings. The idle is lower than it used to  be (1700 rpm, used to be 1900-2100), and I havent touched the idle adjustment screw. The engine also dies every now and then when I abruptly open the throttle a small amount from closed. And every time I try adjusting the fuel screw, nothing happens at all except for when I turn it in all the way, the idle will go up a little. I dont know how it does that because the pilot jet is already smaller than stock. All these problems seem worse when I ride in cooler temps. So I'm assuming my bike is running too lean.

The only thing I can think of is putting the 45 pilot jet back in, and maybe raising the needle to 5th clip. Suggestions?

Leave the needle alone, and go back to the 45 pilot.

Put the 45 pilot in, and the bike seems like it only wants to start with the hot start lever pulled in, and it still idles low (1500-1700 rpm) even after turning the fuel screw. Except the idle rises a bit when I turn the fuel screw all the way in. Same problems as before. When I chop the throttle while the bike is idling, it will often kill the engine instead of revving as it should...I'm guessing because the idle is too low. So I ended up turning the idle up a little and have the fuel screw around half a turn out. After doing that, it seems much better.

But I'm wondering if there might be a problem I'm missing, and if it's normal for the fuel screw to only be half a turn out. if I turn it out past that the idle drops a little, and even more after 1 turn out. And why does it usually only want to start with the hot start?

If it matters...I have been testing/riding my bike in warmer, dryer weather at low elevation (San Diego and desert). And I know the DRD exhaust on my bike needs a repack...dont know if that can actually affect jetting.

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