Yz250 exhaust leaking at head

I've searched this topic on this forum and found very good information but I am kinda just looking for a straight forward answer. Basically on my 07 yz250 its leaking premix out of the exhaust where the exhaust meets the jug (see pics). its's not insanely bad but its something i'd like to fix. when the bike is warmed up it kinda drips spooge out onto the ground which is annoying. I know that if the pipe is bent or anything it could not seat right but its in fairly good condition (no big dents), and i know it could hopefully just be a seal. There is red stuff around the port which makes me think the previous owner tried sealing it with some type of sealant. The pipe is a pro circuit platinum pipe and my question is basically if these fmf seals would work, even though its not on an fmf pipe. just don't feel like paying 20 bucks for two oem seals when i can get 2 seals and 2 springs for half the price. 






I've always had this problem with aftermarket pipes, they never fit perfectly. I don't think replacing the O-rings is going to help much. I use permatex ultra copper sealant on the joint and that keeps the spooge at bay. 

Even a normal rtv silicone based sealer will help. 

so just forget the seals and get some good high temp rtv sealant or something? I don't really plan on taking the pipe off anytime soon unless I was gonna replace the seals.

I replaced the seals and springs on mine and it didn't really make much difference

The red stuff you're seeing is high temp silicon sealer. FMF recommends it for pipe to silencer joints, and for the silencer seams after repacking. Just be sure to clean the flange and pipe of all the oil and spooge before using the silicon and you should be good to go.

Thanks for the help! should I just put a generous amount around where they meet and smooth it in with my finger. or take the pipe off and get it on the inside of the pipe then slip it back on?

Inside is much better and more effective. Apply to both side and just film, let it dry 5 minutes before mounting.

looking at the second picture it looks like that pipe is not sitting to good on the cylinder. It looks like about half the flange is showing and most likely only 1 O-ring is touching the cylinder. I would try to fix that gap and also use silicon.

Yep, it looks like your pipe is bent or badly misaligned causing that huge gap at the cylinder.  Make sure the pipe is not up against the frame causing it to be held away from the cylinder.  Someone may have used a pipe intended for an earlier steel framed bike which required less frame clearance than the aluminum framed bikes do.


To me, using RTV on there is a ghetto fix.  If the pipe is straight and the o-rings are good it will seal and not need RTV.


Admittedly, this is a weak point of the YZ250.  Even when everything is right, the life of these o-rings is not that great.

You have 3 problems and 3 solutions.


1. There shouldn't be that much spooge no matter how bad the leak is.  If there is enough unburned oil to drip out the header join, then it also has to be going somewhere else.  Much of it ends up saturating your muffler packing causing other issues beyond a black mess.  Your jetting is too rich. Like stock - too rich. Lean it off. Typically pilot and main jets and needle will be OK.  If it runs worse (eg. lack of response) when leaned off, then it usually means you need the head modified to have correct squish clearance and volume. I'd guess that maybe 1% of stock YZ250 motors don't need this basic fix.


2. The pipe is bent. They are all very soft. Just mild steel. Mark the flange at the tightest point, then remove the pipe, place it on a mat on the ground and hold it with your feet while you put a 1m long piece of broom stick in the pipe and bend it back to normal shape. Be careful. It bends easily.


3. The join is not sealed. Just use high temp silicone. You dont need much. But clean the surfaces first, using brake cleaner. Best thing about this sealant is it reduces metal on metal rubbing wear.

Thanks for the advise guys! yeah it was running suuuper rich since I &%$#@!ed with the pilot air screw. I got it tuned perfectly yesterday with my friend and it was not leaking after I warmed it up today. I found to the pipe is totally bent. It's fully seated on one side then totally off on the other (in the picture above). I picked up some permetex ultra copper a couple days ago so I might just take it of and try to bend it a little to seat better like you said then use some of the sealant as a temporary fix till I can save up and just buy a new platinum 2 pipe.

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