Over the Winter, I removed the backfire screen and replaced the OEM air filter with the Twin-Air Backfire filter, and yesterday, I finally got a chance to find out what the results are.

There's a subtle something that's noticable, but not a dramatic change. I'm basing this on a 20 minute ride, which included practicing some wheelies, which is wherethe improvement ismost noticable. I'm no wheelie master, but from a slow rolling start and just rolling on the throttle (i.e. powering the front wheel up from around 3K RPM,not popping it up with the clutch), I notice the front end seems to come up easier, and I can tweak the throttle to keep the front end up longer. I'm not comfortable with where the balance point is yet, and always eventually drop the front end before I want to, but I was coming up faster and holding it up longer.

I'm pretty sure my jetting is on the lean side (probably even more so after replacing the OEM air filter), but I'm waiting on my TM33 pumper from Bill Blue, so at this point, I'm not going to put any effort into the Keihin. I'm also running with the KDX snorkle, and there's no change to the intake noise. I think after the pumper is installed, I'll havethe more responsive throttle, and be quite content (for now). It's not a big bore, so I'll just have to make do with finesse instead of phsique.

 

Just out of curiosity could you repeat the above experiment without the snorkel?

 

Yeah, I think that's possible ... just without the snorkel, or without the whole lid? It might run even more lean, but I'll give it a shot and let you know.

 

mines in the shop now gettin jet'd without the backfire screen and airbox lid and a K&N filter... should make a decent difference (i hope)

 

Oh really? Is the K&N an anti-backfire filter? I think I would feel safer with the Twin Air YZ filter.

 

its metal meshed which will absorb some of a backfire and its also fabric not foam, so id say its *fairly* safe compared to a stock filter....
and pls tremor no ghey pm's

 

Hmm, I searched for a K&N filter with the wire mesh, but couldn't find one for the KLX250.If it has the wire mesh, then it should be Ok. What's the K&N part no.?

 

I just removed my backfire screen, and I'm using the two-layer UNI foam filter.
Am I stupid to do that? Anyone ever heard of an air filter catching fire after a backfire?
I just want to get out and ride.

 

Apretty simpleway of seeing things is this - if regular air filters didn't catch fire, there probably wouldn't be a need for the backfire screen.

Three things come to mind:
- I don't think carb backfires are a common occurance, but obviously, they do happen.
- Manufacturers will do whatever it takes to keep themselves out of legal hot-water, as long as its cheap and effective, regardless if it impacts performance.
- The AMA includes rules that require motocrossers to have some form of backfire protection (e.g., backfire screen, special air filter, Nomex underwear, etc.)

So, the bottom line:A special backfire air filter is probably worth considering.

 

Is it true that the backfire filter has an extra layer on it? I saw this post on thumpertalk:
http://www.thumpertalk.com/forum/arc.../t-377707.html
I wonder if that negates the effect of removing the screen in the first place?

I think I'm going to have to oil up my stock filter with some No-Toil and put a lighter to it.
Just for peace of mind. This time I'm serious.