07 YZ450 Jetting

I am having a hard time jetting this one. Here are the stats:

2007 yz 450

Uni filter & cage

stock exhaust

48 pilot

Fuel screw set at 1 1/2 turns out

Stock jet needle

165 main

2300 ft elevation

80-90 degrees farenheit

Premium pump gas

The motor surges from 1/8-1/4 throttle when not under load. It runs great everywhere else. I have tried richening the jet needle all the way to clip 7 and also tried the nflp & nfln needles top to bottom. I adjusted the plug gap to .030 from .023. That helped a little. Help!:bonk::naughty:

Your "air screw" is a fuel screw. In for lean, and out for rich. Low throttle openings such as 1/8-1/4 are influenced more by the pilot circuit than the needle, and your fuel screw setting seems to me to be in too far. Back it out to around 2 turns, and start there. You should review the procedure in the manual for setting it.

Otherwise, the jetting looks like what most people are running.

Sorry I ment to say fuel screw. It is set correcty. I turned it in untill I had a lean mixture RPM rise, then back out a little bit.

At your altitude, I think your jetting is a touch on the rich side. At my altitude here in CO at 5280 ft, I have a 150 main jet, 42 pilot, needle at stock setting, fuel screw 1-1/2 turns.

At your altitude in AZ, I would try a 158 main and a 45 pilot.

I am in AZ, almost the exact same temps/elevation. Stock exhaust. Running the spark plug gap at 28.

I am at stock jetting:

160 main,45 pilot, NFLR on the 4th, fuel screw is 1.5 out currently. ( adjusted today at Ocotillo, about 82 degrees out)

Seems to run pretty good with no bogs or weak spots in the power. Hopefully, when monsoon season hits and it is 104 with 85% humidity I won't have to rejet ( like the old 2 stoke), but we'll see.

From what i've seen this bike is hard to jet.Everyone i've talked to at the track and trail has said that even though they got the sweet spot now doesnt mean that its for good.I think this bike needs constant attention when the temp moves more than 2 degrees.Funny,i didnt think 4 strokes were so finicky on the jetting.

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