I recently did a top end rebuild on my 350x and i'm trying to get the jetting somewhere close to being right. I am currently running a 152 main (the rest of the carb settings are stock), the needle clip at the 4th pos., and the air box lid off. It bogs really bad off idle then catches up in the upper rpms. I have done a few plug chops and my plug is a light grey color w/ no carbon on the plug, is this right or is it rich? Any help would be awesome cuz i'm freakin totally lost on this [img]i/expressions/face-icon-small-confused.gif[/img] lol. Thx.

 

Bump.

 

Sounds like it's too rich in the lower rpm's. As soon as you can get to an rpm that can take in enough air to lean it out, then it catches up and runs. You can't run it hard enough, long enough at the rpm that it's bogging down at to get an accurate reading on the plug.

When you say 4th position, where it it? 4th from top or bottom?

 

I moved it one clip above the middle.

 

Okay, then depending on how you answer my question below, I would say what you have done is actually lean it out on the bottom and then it's way rich in the middle and catches up top.

If you move the clip up (meaning that you've lowered the needle) meaning that the needle takes a little longer to clear the opening of the jet orifice, then you have leaned the mixture on initial opening of the throttle. Once the needle fully clears the oriface opening, then it instantly goes to a overly rich situation at an rpm (or intake volume) that's too low for that fuel/air mixture. Once the rpm's climb to a level that equalizes the amount of intake air in proportion to the fuel flow (non-linear) from that particular jet size, the engine will stabilize and run like a champ, so long as mixture is within limits.

Are you using an aftermarket jet/needle or Mikuni? They do not use the same numbering system. It's almost impossible to tune a carb when people mix aftermarket jets and stock needles, and viceversa.

If I were you, I would start over with the stock setup, and adjust the needle one clip down from center and go from there. I'm not sure what the stock main jet size is for your bike, but I wouldn't go higher than maybe 2 or 3 (stock) jet sizes at a time. Unless you have some serious head work, exhaust, intake that are matched and have been bench flowed, I wouldn't deviate from the stock setup too much. Most bolt on performance parts have a generic quality to them in terms of performace increases that they rarely require any radical carb setting changes. They are hyped via marketing and "seat of the pants experiences" that are heard or read about. "I bolted on this pipe and that intake, so I should feel this in the test ride". The expectation is so automatic, the mind says "man, what a difference", when in fact, the dyno would show only a 2% increase in power. Yet the mind said it was at least a 15% increase. Sort of the same theory as a louder pipe, therefore it sounds like it's going faster, when in fact it's absolutely no change in speed what so ever. It just sounds faster. Also, most people "over jet" their machines expecting that they are getting most out of the bolt on mods when they in fact are not. That's what the dyno is for. Tuning the carb to match your engine and the mods you've done, and they are all different. The same 2 bikes with the same mods may end up with 2 totally different jetting setups but yet they yield the same power.

Good luck and keep us up to date on what you did.

 

I agree with the above post "Prez" understands the hype out there. Buy a set of jets from someplace like jetsrus.com so you have a good matched set of jets. Do not buy out of the used jet bin as you will get mixed results. It sounds to me as if you are still lean on the main. I would not change the needle until you get the main correct.

 

Well I just bought some jets from jetsrus.com, I purchased 4 main jets (138, 140, 145, & 150), and 2 pilot jets (40 & 42). That 152 I've got in there is WAY too rich, I did another plug chop today with a fresh plug and it was really fouled up with carbon. Hopefully these jets will do the trick on gettin it dialed in right.