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Twinair Backfire Filter

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I was reading some previous posts on this and picked one up at a local race today. The seller said a cage is not needed. :cry:

Can you run this without any cage at all? I see some use the YZ125 cage?

What's the YZ125 cage doing if there is no screen on it, does it just provide a better perimeter fit? Anyone running the Twinair Backfire filter without a cage, any problems?

I notice my current stock screen isn't dirty per se but gets No-Toil residue which drys/hardens and fills some of the screens mesh holes which have to be contacted clean occasionly every 3 months. If there is no screen, is not having the screen going to be a problem, is this residue/dirt going to be sucked into the boot not having that extra layer of screen catching it?

Thanks! :cry:

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Go buy the 250 cage. That's what I used. This mod doesnt really help though if your going to use the flame retardant filter. I didnt notice anything. If you think about it sort of cancel each of them out. What you lose in the cage they add back to the filter with the flame retardant layer. But if you dont use the flame retardant filter and no screen you could burn your bike.

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I wouldnt say it doesnt do anything. It was noticable on both of ours and others find it helps as well. It comes into play at WOT more than anywhere else. So if you dont have an exhaust system that can get rid of the additional intake, it may not do much.

Is it the 250 or the 125 cage? I used the 125 cage on the 450 and it was the same size as the 450's. I was under the impression the 250 was larger and wouldnt fit.

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I was curious too, so I went and checked the Yamaha parts website. Looks like the cage is the same on 125 and 250 2-strokes from 2005 all the way back to 1997. (3JD-14458-01-00)

GO BLUE!! :cry:

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Did you have to do any jetting after installing it? I read on the FAQ the bike might run lean. Haven't touch my jetting since I got the bike.

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My jetting is at 192 for the main, and the needle up one clip position. But I have done several other mods and run a procircuit T-4 pipe. My plug is nice and tan, and the bikes definitely haul.

Put a bigger main in, if it runs stronger you should be able to tell easily. Engines make more hp under load running just on the rich side. Plus it's getting close to cold weather, and that will force you to go up on the main anyhow.

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I have a Factory 4 and still didnt see anything. Also I ping off the rev limiter constantly. Bike is jetted just fine and I use IX plugs. Anyway the only benefit I see from it, is not getting rim grease in the screen.

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gonzo did you cut the rear wall of the airbox down flush with the fender? It could be the combo of them that does it.

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what I found is that it seems to play together as a system. You should try wrapping the header and the mid pipe with header wrap as well. It helps to keep the exhaust gas hot and moving fast out the pipe.

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Having never touched the carb, couple of newbie questions..

1. If I buy a Zip Ty fuel screw or similar, do you have to take the entire carb out of the bike to put it in? Where is this fuel screw, is it the hole underneath and back in where the Idle knob is? I tried sticking a small screw driver up but nothing would catch to turn.

2. For these main and pilot jet changes, do I need to take the seat and tank off (the FAQ mentions you need to for the WRF). Is it easier if I do to try to get to this stuff?

Thanks

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1. If I buy a Zip Ty fuel screw or similar, do you have to take the entire carb out of the bike to put it in?

No. Just loosen the carb clamps, remove the hot start and twist the bottom of the carb towards the left side of the bike.

Where is this fuel screw, is it the hole underneath and back in where the Idle knob is? I tried sticking a small screw driver up but nothing would catch to turn.

The fuel screw is in the recess on the bottom, front of the carb. Use a small hand mirror to find it and you'll see the brass screw that takes a flat-bladed screw driver.

2. For these main and pilot jet changes, do I need to take the seat and tank off (the FAQ mentions you need to for the WRF). Is it easier if I do to try to get to this stuff?

No, you don't HAVE to, but it's a lot easier. You can change the main by shutting the gas off and draining the carb. Then take the hex shaped cap off of the bottom of the bowl. The brass hex shaped piece inside is the main jet. The pilot jet is just in front of it (towards the engine), and can be removed with a small flat-bladed screw driver.

As I said, this is much easier with the bottom of the carb twisted towards the left. To twist it, you need to remove the hot start, and to remove that, you need to remove the seat and tank.

Here is a picture of the bottom of an FCR carb on a 450, which is similar to yours, with the hex cap removed. You can see the main jet in the opening in the bottom of the carb, and the pilot jet is just to the (picture) left of that (towards the engine), out of sight. A little further (picture)left (towards the engine) is the fuel screw.

http://www.thumpertalk.com/forum/showflat.php/Cat/0/Number/1414992/page/0/view/collapsed/sb/5/o/all/fpart/1

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Thanks barton, I'll check it out. Great info to work off of. :cry: Strange about the fuel screw, on that picture, the screw is visible. On my bike, I stuck a small screwdriver up in the hole and it went int a good 1" before stopping.

:cry:

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Yeah, that must be one of the differences with the 450, because my stock fuel screw was completely recessed too.

Also, be careful unscrewing then re-installing the hot start. The cap is made of plastic and very easy to strip. Spares are pretty cheap from the dealer, or there is an aluminum anodized one available as an aftermarket. I think Zip-Ty sells them, but I could be wrong. Search this forum.

One final note. Apply a VERY light coating of grease to the threads on your new fuel screw to keep it from binding to the metal on the carburetor through electrolysis. Same thing on the aluminum hot start cap if you get one of those.

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I just got 2 of the zipty plunger nuts. Perfect fit, and a cinch to swap out. They are absolutely worth the money. Would have been nicer if they anodized them blue instead of red though.

The plastic OEM one strips very easily, and when it does the plunger will pull out of the carb causing the engine to rev really high.

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I second the Zipty Hot start carb nut, they are a great thing. It also reduces the wrench to a 12mm so you can actually tighten it.

Shane

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Ok barton, looked at it yesterday. Found the fuel screw using a mirror. It's actually only about 1/2" recessed. The small screwdriver I was using was actually going to the space around the screw. I found a flathead bit from one of those interchangable screwdrivers that will fit in there nicely. Thanks!

Second,

As I said, this is much easier with the bottom of the carb twisted towards the left. To twist it, you need to remove the hot start, and to remove that, you need to remove the seat and tank.

Why do I have to remove the hot start or is this only for newer models, I don't have the hot start on the handlebars. It's just a red knob on the carb :cry:

When you mentioned clamps, I'm I removing the engine clamp or the airboot clamp or both to twist the carb?

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It's easier to swap the pilot jet with the carb off, but you dont have to. Use the same screwdriver bit as for the fuel screw. If you are facing the carb from the gearshift side, it's just forward and to you a bit of the main jet.

The main is easy to swap with the carb on. Just use a 1/4 drive wratchet, and a 6mm socket. It should only take a second of fumbling to find it. It's on the center line of the bike and to the rear of the access hole.

The hot start went from the red knob that you have to a remote bar mount lever in 03 (or 04 I forget). So the discussion about the nut is not a concern for you.

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