Slightly confused with jetting...

Finally got around to rejetting my 96 Yz 250 that I just rebuilt... First off let me say that I am quite experienced when it comes to jetting a 2 stroke. I race one and own 4 so Ive been around the block. Ive searched for an answer but the only thing I can find with similar symptoms are with 4 strokes and it seems its usually due to lean conditions durring engine breaking. Never encountered it on a 2 stroke with the clutch engaged that doesnt do it while idling.

Jetting should be spot on according to my plug chops. Only mods made were replacing the reeds in the rad valve, new filter, and lubed/ replaced the throttle cable, my current and best performing jetting specs while under load are 172 main, 45 pilot, N3CD needle in 2nd clip postion, air screw 1.5 turns out float within spec. after installing a new spring running Amsoil Dominator at 40:1 50/50 93 pump and 110 race fuel. Bike pulls super hard throughout the entire throttle range. No bog, no sputter, nothing. When I chop the throttle off and drag the clutch/ rear brake entering a corner the bike surges extremely hard like im chopping the throttle. Im confused as to where to beign this process. Seems like it took me forever to get the jetting dialed in in the first place. Bike also does not surge when idling on the stand or durring warm up if I chop the throttle which doesnt make sense to me.

Anyone have any ideas. Doesnt make sense why it would surge while riding but not on the stand if my pilot was lean and the plug chop read perfect while testing. Could it be the spring that I raplaced?

Also plan on getting a JD jet kit for the bike but wondered if this would likely fix my issue or if I have another underlying problem.

Posted this in the Yamaha 2 stroke forum but figured Id post in the correct forum as I may get some additional info in here.

turn the idle speed adjuster out till the bike takes throttle blips to keep it running. it will stop doing that.

That is where its at now and it fixed it but I dont understand why it does this with a slight idle... none of my other 3 smokers have this issue (they barely idle, just enough so it doesnt stall). Im in the habit of getting geared up after starting the bike and after geared up I know its ready to ride. If there is no cure for this with the bike idling then Ill have to live with it not.

I was under the impression the bike was going lean somehow when the throttle was cut after being under load.

Thanks Eddie

its due to height of the slide needed for that particular motor to idle.

Thanks alot... went ahead and turned idle back out and no more surge, smoothed the mid range out as well and tamed that nasty on/ off hit.

Edited by ftball90

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