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06 YZ450 cutting out

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Hi guys, I did some searching first but could not find a thread that answered my question.

I have been running mostly stock jetting with the exception of a 168 main jet and a GYTR fuel screw for the last two years and it has worked great. Three weeks ago the bike felt like it was running fat. I started playing with the jetting and went down to a 165 and eventually to a 162 (my house is at 3000 feet, temp about 80-90). with a 162 the bike was cutting out and falling on its face at 1/2 to 3/4 throttle. I put a 168 back in and now it will die past 1/4 throttle.

I took the carb apart today and was very meticulous in cleaning and inspecting everything and I sure could not find anything that was wrong. I put everything back together, (168 and fuel screw 2 turns out) and the bike still will not run past 1/4 throttle.

I struggling trying to figure this out mostly because these jet settings have worked so well in the past for me. Anyhow, any help or insight would be greatly appreciated.

Bike as it sits now is:

Main Jet: 168

Pilot Jet: 42

Starter Jet: 72

Leak Jet (if any): 55

Fuel screw/Setting: 1.5

Needle/Position: NFPR-4

Pipe: Stock

Silencer: White Bros Slip on



Edited by EburgB
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The top end has some hours on it but nothing ridiculous and the valves are within tolerance.

What about the hot start and emulsion tube would give me grief? I thought I understood this bike pretty well but its becoming very apparent that I do not.

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If the hot start were not fully closing, it can induce a lean condition.

If the needle jet emulsion tube is worn, it can induce a rich condition. It wears and typically gets slightly oval right where the needle enters it.

A high float, rich and a low float, lean.

These are the items regarding the carb tht can change and therefore affect jetting out of the blue.

TPS too, has some effect, unplugging it is a simple test (the bike will go into a default mode).

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I checked the float height, its was good.

The emulsion tube does not appear to be egged out or damaged otherwise and the hot start body is nice and tight in the carb body. I unplugged the TPS and it still dies at 1/4 throttle. I guess Im going to have to go to the dealer :banana:

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Well I feel like a bone head right now. I went down to the shop with my carb and set it on the parts counter and was looking at the drain plug. Apparently the lip of the plug cracked and slid down the plug itself. It never leaked due to the o-ring, and honestly i never anticipated that so I never thought to look. I have a zip-ty drain plug in the mail.

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