Fmf 4.1 Slip on

I am at the point I do not like the stock muffler anymore. It's been a while since riding 450 four strokes and thought the stock system would be ok till I got use to the bike, well I'm ready for a change. From what I've read the 09 ti header is good and really do not want problems with burnt pants or problems changing the oil. So what I need to know is will the Fmf 4.1 ti muffler alone with jetting changes make a huge enough difference. Looking for more bottom and mid mostly. Any other slip on feedback would be welcome as well.

I am at the point I do not like the stock muffler anymore. It's been a while since riding 450 four strokes and thought the stock system would be ok till I got use to the bike, well I'm ready for a change. From what I've read the 09 ti header is good and really do not want problems with burnt pants or problems changing the oil. So what I need to know is will the Fmf 4.1 ti muffler alone with jetting changes make a huge enough difference. Looking for more bottom and mid mostly. Any other slip on feedback would be welcome as well.

From my experiences with slip ons, they dont make all that much of a difference. Little more bottom and mid, but not anything that will make you go wow. If I were gonna spend any money it would be on a full pipe from dr.d I want t

From my experiences with slip ons, they dont make all that much of a difference.
The problem with that is that your experience is not with '08-'09 YZ450's. On these two bikes, just about anything, including slip-ons, will give rather remarkable gains in mid-range power. The 4.1 slip-on will do quite well for the '09.

Thanks Gray, good to know, dont want to spend the money on a new header to replace a near new stock one either.

The problem with that is that your experience is not with '08-'09 YZ450's. On these two bikes, just about anything, including slip-ons, will give rather remarkable gains in mid-range power. The 4.1 slip-on will do quite well for the '09.

I see, my experience is on the 426 so that is very true. I have read on here that the mufflers are restrictive, so it all makes sense that even a slip on helps.

Yes it will make a big performance difference on that bike.

another :lol: for the 4.1,i put one(slip on) on my 450 and it really seemed to wake it up off the bottom,helped all the way around too

Decided to go another route, found a brand new take off 06 complete header muffler heat shield everything for 100 bones. Will post results later.

Well I thought I would try the 06 muffler with the 09 header first and really could not tell any difference. This was around the block ride and not a good test I know. After measuring the diameter of the two headers the 09 is quite a bit larger (better for top end I would think) so I will put the 06 header with the 06 muffler next. By the way the pro moto billet spark arrestor from the stock 09 muffler will not work with the 06 muffler. This kinda pissed me off having to buy two spark arrestors.

Buy a fmf for sure, they are shorter than the white bros, yosh, dr. d, dmc and they are great! I know this because i had a White Bros and my dad has a DMC, and my neighboor has a DR. D

Plus performance wise i think it is the best and most effective for what your looking for. But i also have the megabomb header.

Buy a fmf for sure, they are shorter than the white bros, yosh, dr. d, dmc and they are great! I know this because i had a White Bros and my dad has a DMC, and my neighboor has a DR. D

Plus performance wise i think it is the best and most effective for what your looking for. But i also have the megabomb header.

Tapptout, what year 450 do you have and how is the fitment of the mega bomb. What I really need to know is does it interfere with changing the oil filter. Is it tucked in enough not to burn your boots-pants? Have any pictures?

Finally got around to trying the 06 header and muffler with a moto billet spark arrestor installed. Feels like a different motorcycle, this is the best mod I have done so far. May have to go to a richer pilot as I am at three turns out on the fuel screw but everything else in carb is stock settings. Getting some de-acceleration pop but not real bad. This is a sign of leanness correct?

Have an '06 with a megabomb header and stock muffler, great solid smooth lower end and broad range in power. Buy some header wrap; sure to burn anything below the kneecap!

The FMF 4.1 slip on will make a difference, especially on the 08-09 450's. The mechanical muffler design Yamaha uses in the short mufflers is extremely restrictive. It basically has the effect of shoving a rag in your exhaust. However, if you open it up with a 4.1 slip on, the results will be noticeable.

I have a 04 YZ450 and put the Titanium 4.1 factory FMF slip on and mid pipe still running stock head pipe(cant afford megabomb) and it really really really opened my bike up a lot more power went up 2 sizes on the main jet, and got a air fule mixture screw thats adjustable, the nice thing is that the end cap is removable and you can put the SA screen in there for those pesky rangers. (here in california) but really love this exhaust. and it looks sexy.

sounds insane.

good luck

I know I started this thread about the Fmf 4.1 and now have a stock 06 header and muffler. This is a great combination for me, it woke up the bottom and mid to the point I am satisfied. One richer on the pilot and two turns out on the fuel screw without any other changes. Saved allot of money going this way and realistically it's all that I needed.

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