wr426 v's yzf426 carb set up

[potman1980]

hello peeps.

my wr400 has just eaten its big end and i'm planning to do the 426 conversion on it (400 rod, 426 jug & 450 piston). i have a clymer manual for the 400/426 and have been checking the carb setup for the 426 engine and have noticed that the yzf and wrf 426 both run different main and pilot jets.

the wr runs a 165 main with a 75 pilot air jet and 65 starter jet, the yzf runs a 162 main, 100 pilot air and a 72 starter jet. they both run slightly differant needles but set on the same notch. most of the other settings are the same.

i have a yzf exhaust on my bike and was wondering if i would be better using the yzf carb settings ir would the wr settings be better on my wr engine?

thanks for any input ?

[Pooley]

You can really run either jetting setup with that exhaust, as long as you tune each jet properly. I've run both on my WR with a FMF Q pipe.

I think the YZ setup is easier to tune due to no ACV. The ACV is an enrichening circuit on WR carbs that activates (richenes the mixture) on decel. The YZ does not have the ACV, which is why the jets are different. Make sure you disable the ACV if you go the YZ route. It is and is a simple mod to do, and I've found it makes it a lot easier to adjust the fuel screw while riding, since it does not automatically make a rich mixture on decel. The ACV seemed to mask a lean fuel screw because it would make it rich on decel, and I would never get the tell-tale excessive popping of a too lean mix.

[potman1980]

thanks Pooley, avc out and YZ settings in. looking at the head it looks like the bike has been running a little lean, so any way i can make adjustment easier is good with me.