Question about Factory bike Desert YR 250 Motorcycles

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Need help with setting up my dell'orto phbd 14 bs carb for my mini crosser jus recently changed head for a 44mm big bore 3 port piston so need to reset my carb and dont know how to ? i,e idle screw and air screw settings cheers Andy NOTE MY BIKE IS A MINI MOTO DIRT BIKE NOT A REAL BIG BIKE ....

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  • andy
    andy Sep 25, 2009

    Thanks for your reply bud, But your instructions only point to 1 screw to adjust. My carb has 2 screws , 1 for air + 1 for fuel . I have managed to get the bike to fire up but it is unable to sustaine itself, Just lots of backfires when trying to pullstart it. The bike has been heavily modded even to the point with nos fitted . So will most probrobly need to run quite rich i just cant manage to find the sweet spot between the 2 screws !!! GGGRRRRRRRRR Do i start with both the screws turned completely in ?? Turn 1 then the other or 1 at a time ??? regards Andy



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First get the bike running, turn the idle adjustment up enough to keep it running. start with the air/fuel screw, 1 1/4 turn out. adjust the screw which ever way increases the idle 1/4 turn at a time, wait 10 seconds after every 1/4 turn to allow the engine speed to adjust. As the idle goes up you can use the idle screw to keep it in its normal range. at some point, the idle will start to come back down, this is when you want to start going the other way. idealy you want it set in the middle of the range of when it stopped increasing and when it started to decrease. If you are not able to reach this happy medium within the normal adjustment range, you will need to put the proper pilot jet in and start the process again. This should get you up and running, if it is a generic carb you may will have to adjust the jetting to get the bike performing its best after that, but thats another chapter.

Posted on Sep 25, 2009

Testimonial: "managed to get it running now as i now have a propper top head gasket ,lol still trying to find the propper idle setting ,lol tweek turn + hope , andz"


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