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power for the sand

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my 250 is bone stock except for a uni air filter and a dr.D exaust. i want more power. i was thinking about a JD jet kit, a power now and possibly an I cat. does anyone have experience with any , all , or a combonation of these products ?

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The Power Now is strictly a low end thing, you're after high end. From your list I'd do the JD jetting kit, plus an Iridium plug and also pull the backfire screen.

For sand nothing beats a big bore kit, something in the 262-280cc range.

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i have thought about regearing it but for the sand i wanted power and by regearing it my top end will be crap. i feel i will be running through the gears faster than i would like too. maybe for the track i will think about regearing it. thanks :thumbsup:

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I dont think the icat will work with an 03. It's supposed to go between the coil and the plug, and the coil is on the plug for 03 right? It's been a while since I had my 03 but I think thats right.

I wouldnt pull the screen until you get a twin air anti-backfire filter. There is always a chance a backfire could happen, and there is no way for you to put it out if it catches fire. The filter is like $24.

Running a 50T rear wont hurt the top end much at all, and I have found it lets me run 3rd nearly everywhere on the track. 3rd is a sweet gear on these bikes.

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cool thanks for your help i have not yet done the 50 tooth i was waiting for the stocker to wear out and its about there. and the i cat, i have also heard it wouldnt work for the 03 but i didnt think it would hurt to ask. looks like i am going to be doing the jet kit, 50 tooth and a power now :thumbsup:

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I wouldnt pull the screen until you get a twin air anti-backfire filter. There is always a chance a backfire could happen, and there is no way for you to put it out if it catches fire. The filter is like $24.

Is that what the air filter is called, a 'Twin Air Anti-Backfire'? I like the idea of this simple mod, but I checked the TT catalog and while I saw some twin-airs, didn't see one called an 'anti-backfire'... I did notice they had one, though, with the screen laminated to the inside of the filter (the 'dual-stage'?) Any further help with this would be greatly appreciated, its time for me to replace it and I'd LOVE to do this mod (without worrying about the filter catching fire under my butt! :devil:)

:thumbsup:

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I believe they just call it a backfire filter. It comes with their power flow kit (includes filter cage as well), but you can get just the filter under the number part number 152313.

http://www.twinair.com/

They one dendvc posted looks like it. It would be nice if they crossed to twinair's part number to be sure though.

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What's the difference in the grain/granularity of the holes in the "special backfire-resistant layer of foam laminated to the inside of the filter" vs. the grains/holes of the stock mesh? :lol: The holes on the stock screen are pretty large...

Seems to me you take away one set of "holes" to be replaced by another set of "holes" that is laminated onto the filter?! :devil: If the laminated layer's holes are smaller than the stock screen, then that would seem like a step backward for air flow... :awww::D

Rich Rohrich also wrote the following in this thread:

http://www.thumpertalk.com/forum/showflat.php/Cat/0/Number/1354768/page/0/view/collapsed/sb/5/o/all/fpart/1

One last thing as long as we are on the subject of the air filter screen. There is no major change in the pressure differential with or without the screen on the 250F just like it was in 1998 when I measured the original YZ400F. Unlike you Mr. Toluene I've actually taken the time to measure it on my flow bench and so did Dr. Rob Tuluie when he was doing the development work on Doug Henry's SuperMoto YZ450F last year. The end result after a lot of flow bench and dyno time looking for as much usuable power as they could get? Doug Henry's Super trick YZ450F that won Irwindale had the oem filter screen installed in his bike all season.

If Doug Henry's team tried this mod and concluded there wasn't much (in any) improvement, then why bother with it? :lol:

On one hand, many here say it helps, on the other hand a pro team tried it, measured it and concluded NOT to use it - very confusing in deed... :thumbsup:

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I dont think it's the difference in the granularity as much as it is removing one of several obstacles in the airs path. The backfire filter isnt a screen mesh, and I personally dont think it filters as much as a normal filter does. The backfire material has huge holes in it compared to the screen mesh, and it is non existant as far as filtering goes.

I dont know what to say about their results. I wasnt there, and dont know what they tried. It's easy to quote something, and that seems to be happening a lot on here lately. What ever happened to the idea of trying something, and comparing notes if your attempt failed?

What I do know, is that removing it does lower resistance for the intake side and allows more air to flow in. And even though barton was wrong about his thinking the removal would kill the low speed whack response (could be his bike was jetted so it put his over the edge, mine actually revved quicker), he also said it helped at WOT.

Plenty have done it, twinair will sell you the filter to do it, so to dismiss something because another said they cant do it, is missing the opportunity to do it for yourself.

You of all people should be able to relate to that eh Mr. avNow?

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I'm not dismissing anything, I'm all for trying things out and studying the effects if it all makes sense physically. Your removal of the screen makes sense for allowing easier air flow by removing one of the obstacle. I'm just wondering why the race team didn't go with it - probably due to their measurements and perhaps Doug Henry didn't ride the YZ450F at WOT constantly (who really can?). But many of us know, you just can't measure seat-of-the-pants feel such as the gains from the PowerNow (or maybe the air screen removal mod) - the gain is there but it can't really be measured on a machine...

As for me, I'll keep my setup stock since I don't/can't use up all of the currently available power in the upper end, so why try to add even more power up there right? :awww: What I need/want is more power down low for hill climbing and sand blasting - yeah baby! :lol: That will either come from a big-bore job or moving up to the 450 and giving up the agility of the 250, tough call... :devil: I'm thinking possibly a big-bore job in the future... :thumbsup:

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I wasnt pointing at you with the dismissing part. :thumbsup:

The airscreen removal helps all the way from low rpms out, it's just that until you get to wide open throttle do you ever realize you need more power. But removing it helps the bike rev faster so it's a good thing down low too.

speaking of big bores, I just put a 262 kit on both of the bikes. I like them a lot. That added compression really torques the bike up tight. It revs like a banshee because of it. I went with the 262, as it makes the same power as the 280 with less mass so the revs are quicker. That and it's ama ok, so we can still race them in hare scrambles. 2mm is the max allowable for bore increase for the 250cc.

I have a set of cams from hotcams coming for the kids bike. So I'll let you know what that brings. I went with the low rpm cams, to widen the powerband. With the pipe and the screen and the rear wall of the airbox, the big increase was more on the top of the rpms and the cams should fatten up the lower rpms. More power everywhere is what I am shooting for.

Of course all of this is at risk of being dissmissed with a dissertation about someone else telling someone else it wont work and since I read it, I know more than you do shortly. :devil:

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if i was to pull the screen should i be worried about a back fire that might catch my air filter on fire?

This may be just what your looking for...I know I sure move faster when my ass is on fire! :thumbsup:

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if i was to pull the screen should i be worried about a back fire that might catch my air filter on fire?

This may be just what your looking for...I know I sure move faster when my ass is on fire! :thumbsup:

Then all you have to do is ask your buddy to light your pants on fire right when the gate drops! :awww::devil:

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pantsfire.jpg

Hope he doesn't let one rip right about when they did that... :thumbsup::devil:

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