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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
Contact Overland Solutions for all your custom modifications and setup for overland travel.

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  #1  
Old 14 May 2005
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carb pilot air screw - how many turns

Hi,

Anybody know how many turns out the pilot air screw should be (on a 43F)? I've got 4 sets of carbs from XT550 and XT600, and they are all diferent, ranging from half turn out to 2.5 turns out. Any info appreciated

---rob
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  #2  
Old 14 May 2005
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as many turns as the engine needs to run perfectly!


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  #3  
Old 14 May 2005
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... ok

how do I go about setting it up, or more importantly how do I know if its set wrong?

---rob
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  #4  
Old 16 May 2005
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Hi Zebra
My TTR was cutting out at low revs, you replied to a previous thread of mine about this and said you thought it was carb related.well I seem to have cured the problem by turning the piolet screw in making the mixture leaner.I found a bit of info about carb here you might find usefull. http://regis.buead.com/bikes.php?bike=carby
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  #5  
Old 16 May 2005
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Hi Bolla,

Nice to hear from you, glad you sorted your TT out. Did you mention you had a 3AJ model, and if so did you discover the setting of the pilot screw on that carb, while you were trying to sort the TT? I dont know if there is a 'factory setting' for these screws or if they are set up individualy for each bike (which I find hard to believe on a production line).

Anyway - sorry I couldn't get your link to
work

---rob
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  #6  
Old 16 May 2005
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Hi Zebra
I did not touch the 3AJ carbs as they are smaller then the TTR carbs and did not want to mess about with them.
I think the piolet screw is adjusted for each bike but it is only a few turns so maybe its done as part of the pre delivery inspection when they put oil in the bike etc.
It is very difficult to get to the piolet screw they have a special screwdriver in halfords but its £24
I cut and paste a bit from that link.
(Not sure about the air screw if we have one )

Pilot Jet - Up to 1/4 throttle - Controls fuel flow through the idle circuit - Mixture is adjusted by means of the mixture screw -There are two types of mixture screws - Fuel Screws and Air Screws ] - A Fuel Screw, as the name implies, meters fuel - A Fuel Screw will be located on the engine side of the throttle valve, usually on the bottom of the carb - Turn in to lean mixture - Turn out to richen mixture - The engine should have a smooth, steady idle with the screw between 1/4 and 3-1/2 turns out from fully bottomed (gently!) - If the engine requires more than three turns out, the pilot jet may be too lean - If it requires less than 1/4 turn, it may be too rich. - An Air Screw meters air - An Air Screw will be located on the air cleaner side of the throttle valve, usually on the right or left side - Turn in to richen mixture - Turn out to lean mixture - The engine should have a smooth, steady idle with the screw between 1/2 and 2-1/2 turns out from fully bottomed - If the engine requires more than 2-1/2 turns out, the pilot jet may be too rich - If it requires less than 1/2 turn, it may be too lean. Symptoms and/or adjustment - With the idle at approximately 1000 rpm, turn the air screw mixture in slowly until the idle slows or becomes erratic, then begin turning the screw back out until it again becomes erratic. Count the number of turns in between the two positions. Set the position of the air screw between these two conditions, which should also be your smoothest idle . Finally, adjust the idle screw if necessary to approximately 1000 rpm again.
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  #7  
Old 17 May 2005
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Hi bolla,

Thanks for that - its just what I needed. If each carb is set up individualy that explains why these carbs are all set different. The ones I'm putting on are 1.5 turns out, which from what you've sent sound about OK. I'll leave them set as they are, and see how it ticks over as-is (if it ain't broke ...)

thanks again
---rob
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  #8  
Old 18 May 2005
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If it starts ok when cold without choke and badly when hot, turn the pilot mixture screw in, if it starts bad when cold and ok when hot, turn it out.
Don't be afraid to experiment. Your engine will like it.
You can't screw up, unless you turn the screw out more than 8 full turns, then it will fall and you'll need Japanese fingers to put it back in.

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