09 YZ450 exhaust

I did remove the two cones in my exhaust that some people suggested and it did not seem to improve low end on bike.I have two questions I have been thinking about. 1)Will keeping my stock exhaust can with the two cones removed and adding just an after market header work for more power,since the header is to big (stock)? 2) If it will help, will an aftermarket header fit on the stock exhaust muffler?

I am running a modded stock muffler with a PMB endcap and megabomb header. Works well. I can't believe you didn't notice an improvement when you removed the cones from your muffler.?? I certainly did. I actually tried a full PC system and sold it and went back to this setup as it had more power everywhere.

really dvn? i dont like my yoshimura exhuast that much on my yamaha, didnt feel alot over stock :s

You need more then 45 wheel horsepower?

I need more low end HP. Top end is awesome.

Okay here it goes, three ways to turn this bike into a fire breathing dragon is to......

1-If not full system at least get a slip-on, stock can is a buzzkill.

2-Get rid of stock air filter she needs more air than it can provide (twin air works the best for me used them for years).

3-Gear her down you dont need all that top speed unless your drag racing (I use a 50 rear made considerable difference, might even go to 51 yet.)

I gutted my stock can and added a PMB end cap and it did very little for my '09. I ended up with the Dr. D full SS and a '06 ignition and that combo really woke it up.

Okay here it goes, three ways to turn this bike into a fire breathing dragon is to......

1-If not full system at least get a slip-on, stock can is a buzzkill.

2-Get rid of stock air filter she needs more air than it can provide (twin air works the best for me used them for years).

3-Gear her down you dont need all that top speed unless your drag racing (I use a 50 rear made considerable difference, might even go to 51 yet.)

I like the short stock exhaust can. Like I said I cut out the two cones. Also got an after market air filter. Also went up 1 tooth on the rear sprocket,yes that helped. The other stuff did not do anything to the lower end power. I was just wondering if a gutted stock can and aftermarket header would work or just have to get the full system.

LEXX end cap from RockyMountainATVMC on your stock 09 exh(w/ cones removed)...50T rear sprocket

I like the short stock exhaust can. I was just wondering if a gutted stock can and aftermarket header would work or just have to get the full system.

Like I said in my previous post, I am very happy with my modded stock can and megabomb header.

I did remove the two cones in my exhaust that some people suggested and it did not seem to improve low end on bike.I have two questions I have been thinking about. 1)Will keeping my stock exhaust can with the two cones removed and adding just an after market header work for more power,since the header is to big (stock)? 2) If it will help, will an aftermarket header fit on the stock exhaust muffler?

If you removed the cones and it is just a shell now you're losing mid range power plus torque across the powerband.

I'm down with downin on his slip on suggestion. Look for one that comes with a sparky but if you're faced with any sound issues make sure a quiet insert is available.

If you removed the cones and it is just a shell now you're losing mid range power plus torque across the powerband.

I'm not sure where you came across that bit of info, but without the cones, the '09 muffler becomes a straight through glass pack, just like nearly all the rest of them. Not just a shell.

You have to raise the needle one slot and put in a larger main jet to get any advantage out of freeing up the muffler. Otherwise you're just making more noise for nothing. If someone made a smaller diameter headpipe that transitioned into the stock muffler that would be OK, but it doesn't exist to my knowledge.

The '09 YZ (and '08) is one of the only bikes out there that really requires a full system to be right. You can make do with stock muffler mods and headpipe as long as you richen it up accordingly. But the large diameter headpipe is always going to limit the low end snap. The MRD full system is the least expensive best option out there for the '09 YZ.

I had MRD build me a custom exhaust for my 09 YZ.... It pulls hard all through the powerband.

i use an FMF SS powerbomb with the stock muffler.

It added a little low end

FMF said it would not work without their muffler - but it fit PERFECT

i use an FMF SS powerbomb with the stock muffler.

It added a little low end

FMF said it would not work without their muffler - but it fit PERFECT

Did you modify your muffler.

I just ordered a fmf 4.1 slip on muffler. Tech from fmf said no need to jet. just back fuel screw out 1.5 turns. What are your opinions on that? I'm really lacking bottom end right now and have stock gear ratio. I was actually thinking about dropping one tooth on the front since front sprocket is so much cheaper. would that be to much? I have all new sprockets and the back is a twin ring so it wasn't cheap..

Overall i'm hoping to get enough low end power with the muffler to not have to gear it.. Any suggestions?

If you go down one on the front sprocket it wears out the chain slider on the swingarm faster. On the jetting, I would put in at least a size bigger main jet as they are so easy to change anyway, I think that would be a 165 as 160 is stock.

Ok.. thanks. Should i still go 1.5 turns out on the fuel screw?

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