messing with carb swaping on a wr400 - measurements

I put an updated carb in my 99yz400 bike with a 99wr400 motor connected to a 06yz450 carb .That all went well until the carb started jumping out of the motor side boot so i forced it back in and held it their well tightening the clamp , it jumped out again and now i compare carbs more closely

970 stock carb

870 for the 06 450 carb

lips on the carbs are different in the cut outs on the surface the 450 carb has a mid rib i got lazy and cut my collar on my clamp so i could get more bite on the neck of the new carb-it still pops out .

I need to get this sorted out may be my old intake boot has seen better days and has hard'nd up and wont take shape on the new carb neck?

Would a new boot from an 06 yz450  fit on to the 400 head? maybe its longer?

Air box is forward -stretching mounting holes could help

Maybe a better clamp on the boot?

Cut that middle rib off the neck of the carb and it would fit the boot a lot better but its all stretched quite a bit as is when connected?

lets hear some good fixes guys, this was supposed to be a simple swap and an improvement.



I'd first suggest you replace the carb mount joint with a new one.  Yours is likely shrunk a little, complicating things.  No idea off the top of my head whether the 450 joint will fit.  The '06+ won't because it's a different design, but the '03 might (5TA-13597-00-00).

thanks grayracer  - today I cut that rib out of the middle with mr dremmell and removed that bullshit spacer coller on the clamp i'll report back but any one have an 03-05 style head to carb boot they could measure for me ?

The spacer collar is not bullshit.  The collar first controls the amount that the clamp can compress.  This is so that the clamp isn't cinched down so tightly that it gets cut into or starts splitting from over tightening.  Secondly, it allows the clamp screw to be run down and tightened against something solid, so it has a better chance to stay tight.  If it seems to clamp too loosely, it's usually because of the sleeve shrinking over time, and replacing it cures that problem.

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