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Explain Air Screw on FI 4T

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Can someone explain what the air screw is for?

Manual says dint touch it. Where should it be? What does it do?

I have a friend who bought a 350 second hand that doesnt run quite right. Trying to cover all the bases. How can we determine if this is set properly or adjust it to where it should be. Doesnt the stepper control idle air control?

Thanks

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It is the idle adjustment screw used during calibration of the stepper motor. You can turn it if you want, but it will just make it run worse.

 

 

Edited by KRAYNIAL
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18 minutes ago, KRAYNIAL said:
  1. It's a fuel screw, not an air screw
  2. It has two functions: triming the pilot jet size, and fine tuning the idle air/fuel ratio independent of the slide
  3. There is a very *specific way to use it, but first, you need  to:
  4.  on the fuel screw: put in a brand new oring, and make sure the washer and spring are present. oring/washer/spring/fuel screw
  • * start the motor, get it hot
  • shut off motor. adjust fuel screw to 1 turn out from 'soft' full in. start motor. Start motor.
  • adjust idle with idle screw as low as it will go and still idle
  • turn the fuel screw OUT to raise the idle. It should stop raising at about 1.5 turns. ** more on this later
  • if you discover it takes less than 1 turn to get the highest idle using the fuel screw, your pilot jet is too big. More than 2.0, and it's too small
  • ** once you have found the amount of turns where the idle stops rising using the fuel screw, stop.  Figure out how many turns out this is and note it for the future.
  • Start the motor with your new fuel screw base line. Now 'blip' the thottle and listen to the rpms drop. Ultra fine adjustment (1/16 turns?) will allow you to find a place where the idle drops really fast. This is the 'sweet spot' for your specific current air density. Eacy time you ride, after the motor is hot, you can re-visit this, if needed.

If the carb has more than 150 hours on it, you need to replace the wear items on the carb:

  • replace the fuel inlet orings
  • replace the slide plate seal gasket
  • replace the emulsion tube (needle jet)
  • Inspect the float needle and seat for wear
  • re-set the float height

If you do all those things, and the carb is not past it's life, the carb will work like new again.

Never ever ever use automotive carb cleaner on this carb. Never soak this carb in parts cleaner. The carb has an internal body seal, that if contaminated by solvents or un-treated ethanol, with acutally melt, making the carb seem un-tunable. The body seal can be replaced, but it's tedious.

 

 

To be clear, FI in title was meant to convey fuel injection.

In the manual it says touching this screw voids warranty, and gives no information on what it is for. Why is it even there? Stock setting? Issues it causes.

 

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9 minutes ago, Josh Rowe said:

To be clear, FI in title was meant to convey fuel injection.

In the manual it says touching this screw voids warranty, and gives no information on what it is for. Why is it even there? Stock setting? Issues it causes.

 

It is the idle adjustment screw used during calibration of the stepper motor. You can turn it if you want, but it will just make it run worse.

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42 minutes ago, KRAYNIAL said:

It is the idle adjustment screw used during calibration of the stepper motor. You can turn it if you want, but it will just make it run worse.

The question in this case, is if the previous owner moved it could that be causing the current issue. The issue being the bike will not start without turning the throttle a bit. 

Trying to eliminate possible causes.

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4 hours ago, Josh Rowe said:

The question in this case, is if the previous owner moved it could that be causing the current issue. The issue being the bike will not start without turning the throttle a bit. 

Trying to eliminate possible causes.

If the previous owner moved it, all bets are off. Your dealer should have the Beta tool to see where the stepper motor calibration is.

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9 hours ago, Josh Rowe said:

The question in this case, is if the previous owner moved it could that be causing the current issue. The issue being the bike will not start without turning the throttle a bit. 

Trying to eliminate possible causes.

If you havent checked valve clearances then do that first, I have found with all my FI bikes Kawa and Yamaha that when the valves start getting tight you need a bit of throttle opening to start the bike 

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On 9/26/2019 at 6:27 AM, Shawn250 said:

If you havent checked valve clearances then do that first, I have found with all my FI bikes Kawa and Yamaha that when the valves start getting tight you need a bit of throttle opening to start the bike 

Met a "high up" from Beta recently. We talked about this issue, and others. Sounds like the transmission side intake valve has been damaged by dirt and is driving itself up into the head. That valve has been out of spec multiple times this season. Basically after each ride. 

I will follow up. We are going to rebuild the top end, but that may be a project that gets deferred till winter when we have nothing to do! 

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if you are needing to continuously shim the valve after each ride then thats your starting issue, just bear in mind the valve is wearing thinner and at some point can break and damage your motor, dont leave it too long to replace the valve. Also consider stainless steel valves as they last longer.  

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