Fuel/Air Screw adjustment question

7 replies to this topic
  • Toobold30

Posted March 18, 2005 - 08:56 PM


Hey guys. I had to adjust my fuel/air screw today.. I had posted earlier i was having problems.. My question is, do you think i hurt anything by running it for a few mins. down the road before i adjusted the air screw.. She was popping and sputter pretty bad. I rode it maybe 10min like this...Thanks and yes im a worry wort.. :)

  • grayracer513

Posted March 18, 2005 - 09:56 PM


If it runs OK now, don't sweat it.

  • tnl

Posted March 19, 2005 - 01:37 PM


If it's popping or sputtering on deceleration do you screw in or out the fuel/air screw?

  • yamahazinger

Posted March 19, 2005 - 04:06 PM


i think since you have an 05 450 you turn the air/fuel screw out for rich and in for lean. In your case you are lean so you want to back the screw out a couple of half turns at a time until it gets better. So just start it up and let it run for a minute then back the screw out at half turns at a time and see how it runs.

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  • grayracer513

Posted March 19, 2005 - 05:19 PM


Bear in mind before trying to correct a decel backfire that they can be caused by an air leak in the exhaust. In that case, you would be "covering it up" by making the fuel mixture too rich to get it to stop. Check your midpipe clamp and header bolts, then adjust the idle screw.

  • tnl

Posted March 19, 2005 - 07:00 PM


Isn't it a good idea to get a stock reference point on the fuel screw with how many turns out/in it is? Count the number of turns all the way in from the stock location and record that information somewhere for a baseline reading in case you screw it up. Maybe not if you've been doing this for awhile?

  • grayracer513

Posted March 19, 2005 - 07:29 PM


Any kind of reccords keeping is a good idea. But ultimately, it's the engine that gets to decide how the jetting needs to be adjusted.

Here's a good run down on how to: (it's for a 250F, but it works the same way)

Adjusting the FCR Fuel Screw

  • WRookie

Posted March 19, 2005 - 07:32 PM


1 to 3 turns out seems to be the consensus on pilot screws. If your motor runs better with less than one turn you need a leaner pilot screw. More than 3 turns out and you risk the screw vibrating out so a fatter jet is called for.

Decel popping tells me you are lean. I had the same problem with my 05. I'm running a 48pj and 170mj. From 1/2 throttle to closed the pj change stopped the cackleing. Full to half throttle decel popping might have been taken care of by raising the needle but I was in a dusty parking area at the time and switching out mains was easier. It has been a little warmer since then so I have adjusted the screw in half a turn. I don't think I will need the stock 45pj until we hit summer temps.

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