Does anyone have the straight scoop on doing this as opposed to rejetting? I thought I had seen this, but did a search and couldn't find anything. I'm planning a trip to Colorado (from Arkansas) and don't want to rejet for a one week trip. Thanks.

 

We have lots of mountains here in Calif., so we do lots of high altitude riding. My bikes are jetted for sea level, and I have two TPI valves (http://www.thunderproducts.com/tpi_valve.htm) installed in the airbox lid. As we ascend into the mountains, we open the valves and that gives the engine more air to make up for the thinner air at altitude. Then we close them again as we descend. The system works well!

Or, you can drill some holes (better yet use UNI 1" round filters) and cover them with duct tape. Take more tape off as you ascend, and replace it as you descend.

 

What i did was cut a square out of the top of the airbox lid and before that i accidently bought the wrong uni air filter for my 400. So I took the and cut it out so it laid flat and took a staple gun and just stapled it to the airbox lid. Much better than paying $120 for a K&N airbox filter lid. Just $20 and 30mins for me and much better performance and you dont have to clean as much as putting just holes or taking the lid off.

 

The TPI Valve is the same idea. It has a filter, so you aren't totally exposed to the elements. As I recall, they are not particularly expensive. One thing about the TPI is that you can close it for a water crossing. They certainly aren't waterproof, but anything helps.

 

I live in CO, I put a K&N on with outerwears on my o5 rancher and drilled my lid. I didn't rejet. I've riddin this thing to the top of redcone pass http://www.binderbulletin.org/travel/redcone.htmto 12,801 ft above sea level and have no trouble. Most of my riding is between 9-11 K Just get you a K&N man, you can drill holes and when you get home cover up the holes![img]i/expressions/face-icon-small-wink.gif[/img]

 

Sporter I don't have an html attached to my pictures so I can't post some killer pictures of redcone pass, If someone tells me how I will post them. otherwise send me your email and I'll send you some pictures. I'm at friskidog@yahoo.com
John

 

One issue you have to deal with is not forgetting to close the TPI valve or retape the holes when you descend again. If your machine is getting to much air at low altitude, it can run lean which may cause problems!

I personally don't trust a K&N vs a foam filter, so think carefully about that one before you make a decision!

 

for what i did with my airbox lid and putting a uni filter on there, should i rejet. If so so what would you recommend?

 

400EX-You might need to rejet, depending on how much you opened up the lid. The 400EX comes JETTED LEAN FROM THE FACTORY (to meet emissions), and what you did probably just made it worse!

Does your machine seem to run hot? Is your spark plug kind of light in color? Does your machine backfire when you descelerate?

For an opened up airbox lid, I like the EHS Racing lid with the Outerwears cover (and a rejet!). That is what I run on my sport bikes (http://www.ehsracing.com/). It is primarily the utilities that I take to the mountains, and I run the TPI's on them.

 

on the stock airbox lid the center is raised a little, i cut a square and stapled both layers of the uni airfilter to it. It does not backfire and does not run hotter.