I have a stock 400EX and I need to know if I need to rejet if it was brought over to another country. The country im bringing it to is Taiwan which is very hot and humid during the summer time. The temperature can reach up to 90 degrees F. Does anyone know if I would need to rejet due to the hot weather or humidity?

Thanks

 

It would'nt hurt to do a plug check and go from there. If am right i think that it has most to do with elavation more than anything. I would do a plug check and then read the plug and see what it tells you to do.
Rusty
R&K Rental

 

what plug check?

 

Check the color of the spark plugs electrode (the tip on the bottom), if its white its running to lean and ur gonna blow ur motor, if its black your running to rich and are getting poor preformance. It should be a brownish color.

 

To check the spark plug wouldnt I need a special tool to tighten it?

 

Cyba:

I don't think you have to be concerned about relative humidity, but air density is affected by your altitude above sea level. In the reading I've done, it seems most jetting references take into account fairly broad elevation ranges, ie. sea level to 2,500 feet, 2,500 to 5,000 feet, etc. The air density affects your fuel / air ratio. If there's too much air in your mixture, you'll run lean, which typically is indicated by decent acceleration to about 3/4 throttle, then power drops off and you'll also get back firing. To little air in the mixture and you'll run too rich. Rich condition will cause a rough idle, hard starting with strong fuel smell, and backfiring at lower RPM from idle to 1/2 throttle. The spark plug will foul easily and will be wet with fuel when removed shortly after running, or attempted starting.

If you suspect you're too lean, I've heard of people using duct tape to tape a portion of their air filter element to restrict the amount of air going to the engine. This is done only as a diagnostic tool and should not be considered a permanent fix. Try taping across a portion of the filter, say a third of the surface area and see if there's any improvement. If it gets better, try taping across an additional portion of the surface area. In this case, you would probably want to consult your dealer for a larger main jet to richen the mixture. You can also pull a little choke to add more fuel. If choking helps, you're likely too lean.

If you suspect you're too rich, you can try removing the air box covering either partly, or fully, to allow more air to balance the "too much fuel" condition. Again, this is for diagnostic purposes. If this were the case, your dealer might be able to recommend a smaller main jet to reduce the amount of fuel in your mixture.

You don't necessarily need a "special tool" to tighten your spark plug, a deep socket of the right size will do the job. If memory serves, mine takes a 13 or 14mm.

A few words of caution:
Don't overtighten your spark plug. Without a torque wrench to check the proper torque when installing, you'll want your plug to fit snug, but not tight! Make sure you reinstall the plug with the washer, if it has one. The distance of the electrode on the hot end of the plug is critical in relation to its distance to the top of the piston.
Also, don't be tempted to use the incorrect tool to remove, or reinstall, your plug. Rounding of the shoulders on your plug could cause you a great deal of aggravation and potential harm to the plug and threads, which of course is your cylinder head!
Worst of all is overtightening of the plug to the point you strip the threads in the cylinder head!

 

don't worry cyba , it will run fine over there. besides, you really have to wait until your actually there to do any fine tuning.

 

Thanks for the replys guys!

I think I will be riding at both sea level and at higher altitudes since most places are in the mountains. Correct me if im wrong but you said temporarily I could tape my air filter up to reduce less air in. Now does that apply to riding at a higher altitude? If it comes down to changing jets or whatevers i dont mind learning how to do it, its just a pain becsuse on my 400EX the service manual says I need to remove my carbeurator in order to change it. Now it would be a b1tch to change it back and forth everytime i go riding. Change to a bigger or smaller jet requires alot of tuning also right? Its not a screw where I can just turn and tune it from the outside of the carb is it? I mean I would have to change the jet sizes back and forth if I were to ride it in diff altitudes. Sorry for asking these newbie questions [img]i/expressions/face-icon-small-smile.gif[/img]