Jetting questions

[Adam F]

I have a few simple questions about cold starting and jets. I realize this has been discussed alot here, but I could not find these specific answers.




1) I read that using a #42 jet will help out with cold starts. My 2002 300ex takes about 5 minutes to start in the cold. It is quite disturbing to pay $4500 and have the thing run like a $200 junker when its cold. But my question is this. How will the #42 jet affect my quad in the warmer weather? Now that it is getting warmer out, cold starts wont be an issue.


2) I will probably use the jetting instructions in the FAQ section of this site. But will it be the same on a 300ex? If not, does anyone know where I can find a good writeup? Or should I go out and buy a service manual? My buddy has one for his 2000 300ex, maybe I should borrow his?

3) Down the road I plan on adding a free flow exhaust. Something that will gain bottom end, as I only do trail riding and need that extra torque. Will me changing the jets affect the performance of the bike with the above modifacation?





Thanks for your help!!

[Adam F]

Anybody?

[Atomic83]

I know on the 400ex the stock pilot is 38 thats why people go up to 40 or 42. I have a 40 in mine and it helped a little. I don't know if the stock pilot jet is the same on the 300 or not.

[Adam F]

Please? Anyone have an answer?

[NVR2L8]

Question 1. I think the stock pilot jet on a 300EX is a 38, so I would think you could safely go to a 42 for better cold weather starting and not have a problem when the weather warms up. I know that my wife's 300EX starts and idles better after going to a 40 pilot, regardless of the outside temp. If you go up a few sizes and it begins to develop a starting problem after it's warmed up or when it's really hot outside (hard starting as if it's now getting too much fuel and/or loads up a bit after starting), then you should be able to compensate for this problem by adjusting the fuel screw in a bit. BTW, it's not uncommon to have to make adjustments to the fuel screw between summer and winter riding conditions, since the pilot jet only sets the basic air/fuel mixture at idle to 1/4 throttle, and the fuel screw fine tunes the adjustment.

Question 2. Jetting is jetting, and is basically the same for all engines. I don't know of any specific 300EX writeups though, but the one in the FAQ section here should provide enough information for you to jet your machine. I have the factory Honda 300EX service manual, and it really doesn't address how to jet the carb.

Question 3. If you rejet now and only add an exhaust system later, you should be okay with the larger 40-42 pilot and leaving the needle on the stock 3rd groove position, but you might have to increase the size of the main jet. Keep in mind though, that what you do to your jetting now won't affect performance after you add the exhaust--instead it's just the opposite...a free-flowing exhaust will affect performance of your engine and you'll have to jet accordingly for the increased air flow. What I'm trying to say, is that if you jet for the configuration of your engine now, but make changes to the intake or exhuast in the future, then you should jet accordingly to get the best performance from your engine. Clear as mud? *LOL*