Ive replaced the accell pump diaphram and float needle several times now, ive disassembled and cleaned almost the entire carb, including the tamper proof screws. i think that i have a vaccuum issue, when i can get it to run, it spits and sputters badly but i can hear the vaccum control valve assy chattering and when disassembled i can feel some slop between the parts but im not sure if the "slop" is with in spec. ive also replaced the spark plug recently, i run turbo blue/110 racing fuel because when i run 91 or 93 the bike runs worse and i have to remove the float needle and clean before every ride. any suggestions?
SOURCE: hesitation problems 2003 yamaha wr 450 f
sounds like a jetting issue. change the main jets starting from the largest one you own and work your way down.
SOURCE: 04 yfz 450 wont start with electrical start
i have a 04 yfz 450 quad. the compression ratio like yours is extremely high. ive had my battery go bad and found that another battery other than factory would turn over the engine, but would not start. i paid the 100 dollars for the factory battery and it fired right up. because of the high compression you need a high cranking battery.
SOURCE: Cleaning Carb Jets
not to a trained ear also go by rpm and spark plug color
NOTE: use copper wire to clean jets, sync is just thottles are same position as all carb's just leave them adjustments alone will be fine if are out use a 1/8 drill an place in between piston/butterfly to carb bore to sync/calibrate
better use a manometer for adjusting screws
depends on condition of org parts
worn = richer running
new = lean an clean
also if changed the exhaust system need to
re-calibrate carbs for max performance
SOURCE: carburetor adjustments yamaha 450yfz 2004
Turn both the air screw and throttle screw inward until they LIGHTLY seat. Now back each one outward one and one half turns. This is the factory setting. I am going to give you a web site where you can download a free PDF factory service manual for a YZ450FR. I believe the model is a bit different but the carbs are the same.
Go to this site and you can download a free PDF service manual. The site may take up to 25 seconds to fully load the list of manuals. It is worth the wait. www.carlsalter.com/motorcycle-manuals.asp The service procedures are there in detail and a lot of diagrams and photos. Don't mess with the pilot screw unless you have to, Part #11 in the diagram.
Can I get a Very Helpful" rating out of this?
SOURCE: how do i remove and clean the carburetor on a 2005
The easiest way is to remove the seat and then remove the entire rear sub-frame - the airbox is attached to the subframe, so it will go with the subframe. Loosen the rear clamp on the intake boot. The sub-frame is only held on by three bolts so it's a piece of cake to remove.
Once the subframe is off, the carb will be wide open and easy to remove from there.
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