HMF headpipe fitment sucks! backfiring

[kilabeez0]

I got a brand new HMF headpipe off of ebay. getting the pieces to sit in the head and then trying to get the headpipe to fit into them is almost impossible. the headpipe did NOT want to fit onto the head piece connectors:o it's like one of the pipes wasn't bent enough, or maybe too much?? anyway i FINALLY got them together and put the springs on to hold them together and it's still not that tight.:grr: what a pain in the ***.

i also have it jetted with a DJ165 and it's backfires when i let off the throttle from being pinned. do i need to put the 170 main in, or is it because the head pipe and connector piece fitment?

Lastly the directions said to re-use the crush gaskets from my old exhaust....well i couldn't find any crush gaskets and my bike was bone stock. any help on the back firing would be greatly appreciated.

....on a good note, this pipe RIPS, is MUCH quicker than all my friends with WB pipes, and sounds better than any pipe i've heard out there on a 400ex.;)

[04'400ex'er]

mine does the same. It doesn't fit right and you might start to see suit from the exhaust come out where the leaks are. The main jet has nothing to do with the decel, that is the pilot but I went up like 5 sizes and it still didnt fix the problem. The problem lies in the exhaust leak. I am seriously considering returning for a sparks X6...

[2muchquad]

your crush gasket was probably stuck inside the exhaust port,thats where they usually stay after a while.try getting a new one and put it in there as well,until you fix your leak you could play with jetting til your blue in the face it will pop on deceleration:(

[400exrider707]

The pop on deceleration could be fixed by playing with your mixture screw. That should clear the popping up.

[cals400ex]

first off, if your bike is stock besides the pipe, i say a 165DJ is too much.
2nd, i had to tap on my studs in my head a little bit to get the pipe to line up right. you and lightly tap on them to move them. i had to do this with my x-6 and it is going on very easily.

3rd, the hmf's do leak a bit due to the design of the pipe. however, my buddy runs this pipe with great success and NO popping or backfiring. you need to go up on the pilot jet. my buddy runs a 45 and couldn't be happier. this is on a mild 406 engine.

[kilabeez0]

maybe i'll try the 45.

as for the 165, i have a k&n with no airbox lid along with choke removed, so i'm pretty sure the 165 isn't too big. it rips

[cals400ex]

Originally posted by kilabeez0
maybe i'll try the 45.

as for the 165, i have a k&n with no airbox lid along with choke removed, so i'm pretty sure the 165 isn't too big. it rips


i don't even run that much on my 426, but everyone jets differently. it probably isn't big enough for you to feel a loss though. what elevation you at?

[04'400ex'er]

the end pieces that mount to the head fit fine on mine. The problem was getting the headpipe/midpipe to fit on both of the fittings. they didnt line up right and it took lots and lots of wiggling and working to get it on there. now it is blowing black suit where the silencer connects and where the 2 pipes out of the head come into one. It is hard to really see in there but the only thing I can see is that there is a weld bad and suit is coming out there. I am running a 160 main at 1000ft. I also have tried a 40,42,and now i am on a 45 pilot jet and it is still popping some. Not as bad but still doin it. I tried a 162 and it flooded out bad so I no that the main is really close. but the popping...

[TC426EX]

First of all dude, you need to replace the copper crush washers EVERY time you take the head pipe off. Theyre only like 2.00 a piece or less even and they are pretty important. Those should never be reused. They crush in and fill any space from imperfections between the header and exhaust ports. Keep in mind that an Exhaust leak at the header could cause your engine tempuratures to be higher. So first thing I would do is get some new copper crush washers. Hell, buy 2 or 3 pairs of em so you got em around for next time. If it is leaking from the header/silencer junction, you may want to try some high temp. silicone pipe sealer in there. I used to use it on my 250R pipe a a while back, and it worked great. LRD makes it I know, and Nacs is where i always bought it from... Hopefully those 2 things will help you get it sealed up, and you can concentrate on jetting it right after the leaks are taken care of...

[2muchquad]

you can concentrate on jetting it right after the leaks are taken care of...

thank you tc my words exactly,i didnt want to say it twice:D

[cals400ex]

Originally posted by 04'400ex'er
the end pieces that mount to the head fit fine on mine. The problem was getting the headpipe/midpipe to fit on both of the fittings. they didnt line up right and it took lots and lots of wiggling and working to get it on there. now it is blowing black suit where the silencer connects and where the 2 pipes out of the head come into one. It is hard to really see in there but the only thing I can see is that there is a weld bad and suit is coming out there. I am running a 160 main at 1000ft. I also have tried a 40,42,and now i am on a 45 pilot jet and it is still popping some. Not as bad but still doin it. I tried a 162 and it flooded out bad so I no that the main is really close. but the popping...

the full HMF's that i have seen all leak a little due to the head pipe design. how many turns out on the fuel screw are you?

[kilabeez0]

not sure, i think 4.

This is great, after months of researching which pipe to get, everyone pretty much agreed the HMF was great and not once did I hear anyone say all the HMF pipe's they've seen leak:mad:

ps~~ i still think it's WAY better than the WB e series.

[cals400ex]

i know my buddies leaks a little bit and i have a feeling it may out perform my x-6. i could be wrong but his hmf does make good power.

[TORO1968]

My HMF fits perfectly... This is the first time I've heard of this problem.

[397ccEX]

I am orderin my hmf full next week now.. i dono :mad:
Is this a good pipe i wasnt plannin on throwin down for the ballance series is the regular hmf full for the 400ex gonna do me right or is ther another pipe maybe big gun race series

[wheeltrax]

my HMF full sys. took a bit of wiggling and playing around with to fit fine at first, but it fits good now, and i love it.

[kilabeez0]

power is really good. anyone compare it to the X6?