I had heard this for years from many different sources, but never saw it in print form Honda. Well, I was leafing through the 400EX Service Manual this weekend, and there it was in the Emissions Control section (page 1-23): "The exhaust emission control system is composed of a lean carburetor setting ...". That's why your stock 400 is so hard to start!!

 

In the first days I was starting my 400EX, I was having sooo much trouble doing it. Use the choke, remove the choke, give him gas, dont give him gas.. Sometimes, it was taking 2-3 minutes to get it idle right without the choke on. Then I find out others friend were having the same problem.. Is it because it need to be rejetted? If so, does that mean that the stock 400EX should be re-jetted right away? right after buying it.

 

Looks like it does. I would go 1 size up on the pilot jet.