header pipe

[yellow machine]

Well my plans fell through on getting the DMC system, too many bills. So I went with an E-series slip on, and k&n kit(outerwear, filter, jet kit.) I have a couple questions about the WB pipe. After going to the WB site I ordered a six pack of discs to add to the 12 that come with it.

everything will be here on monday or tuesday, but I am not planning on riding before then so I thought I would get it ready to be put on. I have heard people talk about modifying the stock head pipe by grinding some weld, what exactaly do I need to do to it?

Does anyone have info on how to modify the air box lid with this application?

and finally When I do find some more money, is it possible to put an powerbomb header w/WB slip on, are the pipes the right diameter, or should I stick with getting the WB header.

for now I am just worried about the air lid and the header mods, any help would be great. thanks.:square

[tprender]

Take the head pipe off and look inside of the 2 opening and you will see the build up from the weld. I took a grinding stone and put on my drill and tried to smooth them out the best that I could. If the weld is built up just 1/16 in it will decrease the flow by about 20-25%. I have done this and am running the E-series with 13 disc and have a IMS 440 kit and it runs very,very good. Last week I changed to a 16T in front , I know can run wide open across the sand flats at St. Joe Park with my friends that have Raptors.

[JB's 400ex]

Does grinding that weld down have any affects on the strength of the weld? Did you have to rejet after grinding it down?

[Wheelie]

As far as I know, the powerbomb header will work fine with the E-Series slip-on. The WB header and silencer has to be purchased as one unit, buying a slip-on, then buying the pro-meg header later won't work, the two won't fit together.

The FMF header will cost almost $200, IMO that money would be better spent if put toward a high-comp. piston and cam. As for modifying the airbox lid, if dirt and mud are not a concern, remove it. If they are a concern, either cut six one inch holes in the lid, or cut one 2.5inch hole in the back of the lid.

I am removing my stock header in a few minutes to grind out the welds, I will tell you how it works out.

Hope this helps.....Good Luck!

[Wheelie]

The welds on my 400 weren't too bad, but I did a good 'polish and port' job on the headpipe anyways. It was very easy to do and takes less than an hour from start to finish.

IMO it won't have any negative effects on the strength of the headpipe, and rejetting shouldn't be necessary. From the looks of it, this mod would respond well to polish and porting the cylinder head, as the opening in the headpipe is now significantly larger that the opening on the exhaust ports.

[yellow machine]

Thanks for the help

Pipe still has not come in but I am going to pull the header tonite and do some grinding.

I do like to go through some mud so I will probably do the 2 and1/2 inch hole in the lid.

hopefully by the time I get home it will all be waiting for me today!

I will let you know how it went.

thanks again.

[300EX-Man]

Wheelie: The WB header and silencer has to be purchased as one unit, buying a slip-on, then buying the pro-meg header later won't work, the two won't fit together.

Wheelie u are confused. with the 300ex u have to buy the pro-meg and head pipe seperate. i know cause that is what i did. for the 300 u can buy the promeg meg slip on for $285 at dennis kirk. the header is optional at $120. but u are right the promeg for the 400ex only comes as a complete set.

the power bomb should work on the 300ex. i found it for sale in one of the ads in dirt wheels.

Modifying the stock header pipe is easy.I used a air powered die grinder.It took about 10 minutes of grinding.The first time I did it I was conservative.I didn't notice any gains.So I removed it and really opened it up.I most definitly feel a gain now.I also have a 350x airbox boot.With a 125 main jet I can pull wheelie's up in 5th gear now.Runs much better.


My buddy works at a service station.He gave me a peice of exhaust pipe that is about the same size as the end of the 300ex pipe where it clamps onto the the header.I plan on buying another stock exhaust.Because mine has a big dent in the spark arrestor.Also the stock header pipe cracked twice.(not where I ground on it though)So I plan on buying another stock system.And making my own powerbomb type header.I will put the stock heat sheild back on.It should look stock but run alot better.

I also might be buying another stock carb and have duncan modify it.


I want my 300ex is be a sleeper setup.So far I am doing pretty good.




86 trx250r
97 300ex