YZF426 autodecompress tuning ?'s

1 reply to this topic
  • boostedbenz

Posted March 22, 2009 - 10:47 PM


Ok, so I have an interesting "problem" which is two parted....and not so much a problem I guess....anyway let me get started....

First my bike is a 00 426, with a 07' 450f cam swap, and one other mod which I think is a pilot adjust (red aluminum billet screw at bottome of carb numbered with 1-2-3-4)

I have ZERO starting problems....cold bike starts with choke out within 3 kicks can stay running with choke off after only a minute warming up, on a good day it will start cold no choke 2 kicks

Now after 4 very frustrating trips out I figured out that it will rarely start warm with just the hotstart button out, or in....it will only start warm with hot start AND the choke out. Is this right?

And there are few occasions this doesn't work, and so I will push in the choke....try again and it will fire, but it will start rise in RPM's (to about the same RPM's as a choked cold start) but then peak and immediately drop struggle to run and then die. Is this normal too? My buddies 450f's don't die when pulling the hotstart?

The bike runs fine, and honestly I wasnt' concerned until 3 people seemed oddly perplexed and concerned when I told them, "oh pull the hotstart and choke out"

Response was the same with all 3 "HUH? That's not good bro"

Also can someone point me in any direction where to find information about that billet red knob at the bottom of my carb, thanks! (I'm a fuel injection guy, so carbs are a bit new to me but I think it's a pilot adjust right??)

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  • rufusz

Posted March 23, 2009 - 02:59 AM


First, it's not right to have both the choke and the hot-start pulled out!
When pulling the choke, the engine gets more fuel and less air, while the hotstart does the opposite : less fuel, more air. Already by plain logic you can see that you shouldn't operate them together.
The red alluminum billet screw adjusts the air/fuel mixture when idling (yes it's the pilot adjust). If you can't restart it hot, turn the screw in a little bit, by this making the mixture leaner. Do not turn in too much in one step. Also you can try to kick it with the throttle pulled very-very little (doing so, more air is going to flow in - but ultimate solution is to dial the carb right using that adjustable fuel screw). Search the forum, you will find a lot of info on this.
Good luck.

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