Adjusting Idle Air Screw

[jml]

Hey all, 

 

On my 125cc Beta EVO I was wondering how often should I be adjusting the idle air screw? At certain events above 1000-2000+ feet of elevation the bikes idle rpm drops low (850-900 from the normal 1050 rpm) and it starts to feel a bit like a slouch at 1/4 throttle. Generally these location because of their elevation are also much colder than the sea-level where I live and test ride the bike. I can sometimes bring up the idle rpm to rectify the issue but sometimes it doesn't really help, more turns of the idle screw doesn't bring up the idle. The bike runs perfectly fine at sea level events I'm just wondering if I should be playing with the idle air screw?

[sirdabalot]

Presuming your air/fuel mixture is perfect at sea level. You can try adjusting the pilot air screw, in for richer out for weaker. Higher altitude usualy needs the screw to be turned in up to one turn. Beta Evo air screws are tricky to get at and I fitted a flexible adjuster, from Beta, to enable on the trail adjustments. A bit of trial and error will be needed.

One thing that adds to the issue, is that cooler air is denser than warm, which would tend to make the mixture weaker, but as a rule of thumb, I always try richer first to reduce risk of engine damage

[pschrauber]

As you have dialled in your carb to your home at sea level to - as you stated - good effect. The only thing that happens is that the engine is starting getting richer fueld.

 

This is not a serious problem, the engine should tolerate it but will not run perfect.

 

I too live at 50m above sea level and when I go riding in the Alpes were we start at 1500m there is only a little adjustment to the mixture screw needed to my Beta.

 

I hope you have located the right screw as the air mixture screw works just the opposite way of the fuel mixture screw:

 

Anyway assuming you have and air- mixture screw:

(then the screw is located between the idle screw and the intake of the airbox side):

turning the screw in results in richer mixture,

turning the screw out results in leaner mixture,

 

If you have a fuel mixture screw:

(then the screw is located between the idle screw and the intake of the motor):

turning the screw in result in leaner mixture,

turning the screw out result in richer mixture,

 

How to set up the air- or mixture screws:

Adjust the screw to 1,5 to 2 turns from completely turned in, (standard setting).

 

Start the engine and then adjust the idle screw (in the middle) so the engine runs a little bit higher then usual,

let the engine warm up a little bit.

 

Now by slowly turning the mixture screw out hear if the engine is running higher or lower.

 

If it's running higher turn slowly as long out as the rpm of the starts to decrease again,

were you have found the highest rpm with the mixture screw is the best setting.

 

If the motor is running with less rpm then you have to turn the screw inside until again you find the

peak of rpm of the engine.

 

Now you can turn down the idle screw again to the setting you need.

 

If there is now change at all when you turn the screw then need another idle jet, (should normally not be the case).

 

Et voilà that's it.

 

I recommend to adjust the mixture screw to the fatter side always if you start to go from higher ground to lower ground.

(as already mentioned I just adjust them in the Alpes once at 1500m then I ride up to nearly 3000m without doing any

changes, as richer is no big problem but leaner can easily be an issue)

 

 

Edited July 5, 2015 by pschrauber

[jml]

Thanks guys, I'm definitely going to have a play with the screw next time I'm having issues.