what exactly does the cold start knob do? 2010yz450


7 replies to this topic
  • brentn

Posted September 29, 2010 - 11:44 AM

#1

It's not a choke, this much is clear.

Curious to know if it is actually a switch that tells the ecu to pump in more fuel? Or if it opens up an air passage?
I know when I use it the intake on the bike is louder with the "pumping" noises of the piston/engine. When I push it in (turn it off) the idle lowers and the noises are not nearly as loud.
Any ideas?

  • grayracer513

Posted September 29, 2010 - 11:55 AM

#2

As far as I know, it simply adds air. Roughly the same as the hot start on a carb model. Odd in that way that it serves as a cold starting aid. Cracking the throttle works, too.

BTW, the "choke" on an FCR Carb (as well as most other modern bike carbs) is not a choke either, but opens a passage that allows more air and fuel into the engine through a separate circuit.

  • brentn

Posted September 29, 2010 - 12:10 PM

#3

Yes it is the same on the yz250 keihen carb, doesn't restrict air but allows more air and fuel. When I mentioned choke for some reason I was thinking the old school butterfly valve still used on some small engine carbs....

Funny cause the bike starts ONE kick when the tab is pulled open when the bike is hot. With the tab closed (in) the bike takes 3-4 kicks to start, sometimes it floods this way...
Going to do more testing because I'm sick and tired of cracking the throttle just right on this bike to get it going when hot. I know that this was completely required when I first got it, but now just trying it without cracking the throttle the bike started in 4 kicks... weird... maybe a break in thing?
Going to the sticks today, see how she goes.
I'm thinking I found a one kick hot start button though...

  • grayracer513

Posted September 29, 2010 - 01:43 PM

#4

Yes it is the same on the yz250 keihen carb, doesn't restrict air but allows more air and fuel. When I mentioned choke for some reason I was thinking the old school butterfly valve still used on some small engine carbs....

Everybody calls it that, and if you look at the knob, the icon it's labeled with is a what..? Yep, a choke. :smirk:

It does roll off the tongue a lot easier than, "cold start enrichment valve", though.

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  • brentn

Posted September 29, 2010 - 06:13 PM

#5

Went for a good hour and half trail ride today and tried out a few things for starting.


Engine is hot
With the knob in and 0 throttle it would take sometimes 4 kicks for the bike to fire up and idle. THere were a couple times in which the bike would not start 10+ kicks

With the knob out most times the bike would start with one kick, sometimes two, but would start every time!

Huh...

It's still quicker for me to crack the throttle and kick it. Interesting non-the-less

  • tech24

Posted September 30, 2010 - 03:56 AM

#6

Yes it adds air. If you listen you can here it. It really should be called a fast idle knob or something because its as useful hot as it is cold. I've been trying to figure out a way to install a hot start lever to it but haven't really figured anything out. Bike is a pain to start hot without it or cracked throttle.

I'm also awaiting reports of a possible remapped starting air/fuel ratio in new models to come for a possible ECM swap

Edited by tech24, September 30, 2010 - 04:18 AM.


  • brentn

Posted September 30, 2010 - 09:09 AM

#7

I wonder if the power commander 5 could do this?

  • tech24

Posted September 30, 2010 - 09:39 AM

#8

I wonder if the power commander 5 could do this?


I was wondering too, I'm thinking yes but have no experience with one.





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