Hard Starting, carb questions

1 reply to this topic
  • Daz_426_02

Posted September 27, 2007 - 05:08 AM


Hi Guys,
I am based here in South Africa and could do with a little help please.
Here is what i have....

Yamaha YZ450 2007
Everything is totaly stock apart from a Twin-Air Air filter. Im not sure what size Jets i have as i havent opened the carb as yet. The Bike probably has 50-75 Hours on it. It seems to be running rich i think, it does battle to start a little (hot or cold) One of my mates bought a bike at the same time as i did and his starts much easier. We have the same hours and ride the same conditions. I also have quite a bit of back-firing on de-acel...

I thought about adjusting the air-fuel mixtrue first, if any one has some pics of how to do this i would appreciate it.

Just for the record, altitude is about 2100ft and temp is anything from 52F - 108F and normally 70%+ Humidity

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  • efan450f

Posted September 27, 2007 - 10:36 AM


hey i have an 05 yz 450f and i believe the jet settings are differnet from my year to yours but if it's running fine once you get it started your probably right in wanting to adjust your low speed air/fuel screw... on these models the screw is on the bottom on of the carb towards the front of the bike you can't see it with it on the bike you will have to remove the carb or at the very least loosen it and turn the carb... do this from the left side of the bike and try to rotate it clock wise to expose the screw...this screw is a fuel screw not an air screw so to richen it turn it to the left.. to lean it turn it to the right. the factory settings should be around 1 3/4 turns out from all the way in. i am at sea level in the u.s. but im pretty sure that the higher the elevation the leaner you have to go, so i would check the initial settings and record it so you don't forget then turn it in 1/4 to 1/2 turn and see, if you have to turn it in or out more then 1 whole turn you will need to put a smaller or larger pilot in (if your friend has the same bike w/ no problems you probably won't have to rejet just adjust it) the popping on decel will also go away to an extent these bikes have been known to pop on decel even if it's jetted properly but at the same time it should also start easy, if you can't figure it out let me know the carb settings either by taking it apart and looking or buy a service manual (which i would recommend doing anyway)and check that if that helps if still no luck contact eddie a.k.a. "burned" he's the jetting expert here and has helped me on numerous jetting questions and im sure he could help you . good luck.. post your results so i know if you got it fixed

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