Need more mods -- More Power please.

Ok, went down to Kentucky this weekend and had a blast, hit things I didn't expect too. Hill from H**l, rocks, bolders, river beds...

Yet, i was trying to keep up with CR 250's, and XR450's.. My XR400 was no match...

Mods todate --

1) Header welds ground out -

2) New air cleaner

3) Dropped one tooth on front sprocket..

Still have stock muffler and stock carb setup -- Seems to give out about 1/2 through a gear -- could be jetting (Others have suggested mods to it) ...

I live in Central Indiana ---- Mostly flat land, yet I travel south and to Ohio alot..

Can you help..

Yeppers, cant do one without the other, re-jet. Baja designs is real helpfull for a jet kit if you cant get info at your local shop. Someone here will be responding with good info. I ended up putting a pumper carb on, I couldnt be happier.....well, thats not true. As we speak I'm having Barnums do the porting, valves, cam and 426 kit. But I was happy after the pumper carb, just started using a bit of oil, so I figured what the heck. It should be up to 43 ponies when done according to Rob Barnum. Thats just about YZ426F territory.

On my XR400 I cut the entire top out of my airbox, which helped out alot. I also installed a White Brothers "all around cam" that made a huge difference, my filter gets dirty quicker now, but it added more power with the proper jetting. A new exhaust set up is a must if you want more power, whether it's just a new insert, or a full set up, you will gain more power. I also cleaned up and polished both the intake and exhaust ports of my cylinder head, and matched up the intake carb boot to the cylinder, that made some more power for me.

Good luck,


Do a search of "gordons mods"

There's a pretty complete list of XR4 mods you can do to unleash the beast!

You need to open up your airbox and re-jet accordingly.

If you don't have the coin for a new exhaust-- I would definatley recommend doing the "gordon's mod" untill you can.

I drilled a few holes in my stock exhaust tip while I waited for the Vortip insert to come in. Amazing Difference!



Gordon's Mods

Dirty Filter...

My friend up in Oregon turned me onto this trick. Add a pre-filter over the airbox opening.

I use Helix course prefilter foam, available at and many auto stores. Just cut it to fit between the frame rails and over the airbox opening. One sheet will make 4 prefilters for an XR400.

Oil it up just like your filter. It's amazing! My Uni-filter stays nice and red while the pre-filter turns brown.

On the note of a pre-filter, I just took some of my sisters panyhose (shhh, don't tell her!) cut off the toes, and streched the toes over the opening on my airbox. I know it probably isn't the best answer, but hey, I'll be it is the cheapest!

Couldn't find the Gordon mods with the site revisions, but I'll dig more. The pumper carb suggested in the XR story was revealing. Anyone with experience with the McCords power flow mods for the XR carb, or is the pumper the best solution?

Gordon mods :)

Also needing suggestions for an inline Fual filter, my float has gotten stuck twice now, and is a pain in the rear to get unstuck-- not to mention the screws used on the bowl are not in an easy place - thinking when I change out carb to replace the bowl screws with - alen head screws.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now