Jetting a atv?

[M00km0nster]

I upgraded my air filter/spark plug and oil filter to K&N brands on my 2 x 2005 yamaha 350 4x4s. Now I constantly lose the engine when climbing at low rpms, the negative effect I was looking for. Bottom line is after calling around, it was suggested I re-jet the carb. Googling this and reading up on it doesn't make it look too hard till i get into my atv and start fiddling with it. I'm thinking of taking it in with my head hung low and letting a shop do it. Is jetting easy to do or is it really something a Pro should do? $75 x 2 is just a little to much to stomach for some Yahoo to twist 3 screws while he swipes the last 150 bucks to my name.

[MY T PIMP]

I've also been interested in jetting my bike (honda 250ex) but have been unsure. So any help, give us a hand?

[RugerShooter]

It's easy to do yourself if you know what size of jet to get. The shop should be able to suggest a size to put in. All you have to do is take the Carb apart.

If I remember right you take the bowl off the carb and the jet is up in there. It is a little hex shapped piece of brass with a hole in it that just screws in. it will have a number stamped on the top of it, and that is the size.

[Stuck N Utah]

I just did a rejet on my honda rubicon the hardest part was getting the carburator out of the frame, as for replacing the main jet peice of cake remove the bowl and it screws in and out. I bought the dynojet kit from rockymtn atv and it has easy to follow instructions. The kit also comes with multiple jets and an adjustable needle. I think if you have any mechanical sence you should be able to do it yourself.

[Iceaxe]

First off.... how did you "upgrade" your spark plug. There is no such thing.... you might have bought a more expensive plug, but you probably really just got hosed. I found NGK plugs to be my preferred choice.... I'm thinking your "dying" problem might be plug related..... first rule of modification is to do one thing at a time so you can judge the results. Your "upgraded" plug is probably in a different heat range and has some what the same effect as rejetting.... but without near the control.

Next.... I have probably jetted several thousand motorcycles and ATV's....

First.... changing an air cleaner should not effect jetting unless the old air box/filter was staving the motor. The part I would be concerned about with your report is are you now getting enough filtration? Dirt and dust is the kiss of death to an ATV motor and K&N is famous for sacrificing filtration for air volume. After rebuilding several thousand engines I'm not a big fan of K&N products.

Now for jetting, it's not to difficult.... but first you have to know what jets you are running. You will need to know the main jet and pilot jet size. Probably one or two sizes down on the main, one size on the pilot and you will need to drop your needle one or two clicks. Go down one step at a time on each.... run the engine hard and then shut it off without idling.... pull your plug and see what it looks like. You are looking for a nice tan color. If you start to see a whitish color you have gone to lean. Black are really dark brown and you are to rich....

A good shop might be able to tell you where your jets should be..... or they just might make something up that sounds good so they don't look like a bunch of idiots... you can never tell with those guys..

[Iceaxe]

PS... most shops I've been around rejet the ATV as part of the "500 mile" tune-up. You really want to run the motor on the rich side while breaking it in.... which is why they usually rejetted at the first tune-up.

[Stuck N Utah]

something else you may want to know!!! I called honda to find out what the stock jetting was and what they recomend for high altitude because I bought my atv in anchorage at sea level. Turns out all the atv's solt at newgate honda get rejetted upon arrival from a 162 to a 155 main, well at least the rubicons.

Some times you can tell if its running to rich or lean by removing your airbox lid or covering the intake a little to see how it responds to more or less air.