spark arrestor for YZ400f?

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Oct 13, 1999
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#1
Has anyone tried one of these on their YZ 400f? www.bmp.motox.org/yz400.htm Seems like a good way to go with a spark arrestor without the expense of a new pipe. How did it affect performance, sound, etc.?

Thanks.
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Brandon
 

BadgerMan

Mi. Trail Riders
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#2
I have one on my YZ250F and it works great. A little quieter than stock with all eight disks installed and I also notice a little more low end. Removing two disks lowers the noise level but also hurts performance and causes the off-idle hiccup to increase.
 

Dan

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#3
I have one on my yz400. It is worth if you have to be quiet, but other that that i have an fmf i use. I dont like to run it alot because it does hurt the power, not to mention the throttle response suffers also(something the 400 needs). I didnt have spot on jetting though, the only way you get most of your power is if you run all the disks, not to much queiter though. I bought is because it good to have a spark arrester around for some occasions.
 

MWEISSEN

Whaasssup?
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#4
BMP disk kits for YZ

I've got a '99 WR (with YZ pipe) and an '01 YZ250F that I've installed the BMP kits on. This weekend I ran an event which required 94dB sound limit. At 5 disks, the YZ250F passed at 92.6dB. The WR didn't. I reinstalled the stock WR pipe with a White Brothers Vortip (faster to do than removed a disk believe it or not). This passed at 92.5 dB. I probably could've passed with the BMP at four disks.

Down at 5 disks we really didn't notice that much real-world power loss over the 8 disks that were "stock". I'm sure it's there, but it didn't affect rideability.

Going back to the WR exhaust on the 400 did cause a performance hit on the low-end, but not enough to ruin a day's ride on!
 

Dan

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#5
hOW TIGHT do you tighten the bolts holding on the plates. I dont want to over tighten them on mine and i dont want to leave them loose. So about how much torque do you put on them? I have to put mine on soon :silly: because i am going to start building a track and my dad will not shut up. So guess i will stick it back on, untill i go to a motorcross track.
 

MWEISSEN

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#6
I haven't checked a torque value, but I just snug them down. I've been concerned about crushing the stamping down also, so I watch it. I haven't had any loosen up. Oh yeah, put some Loctite on the fasteners and they'll stay in place better.