I am having trouble getting enough airflow into my carb. I installed a very large 45mm flatside carb and it runs rich in the mid range with the leanest standard jet needle with the needle in the lowest position. Also, it seems to need a smaller main jet than normal to keep full throttle running peak. The stock airbox setup has a rubberlike boot that run from the carb to an airbox where the filter is located and has a lid that is sealed tightly - see a pic here: http://www.atvconnection.com/editor/...ircleanerb.JPG I removed the airbox lid and that helps, but it still runs a little rich. I have a high flow K&N filter to use which will also help, but it is not good for the dunes.

Are there any good URL's that cover airboxes 101 for dummies?

 

K&N's work great for the dunes. I have never had a problem with mine. If you are having that much trouble with the jetting you might want to take it to a shop and have them tune it for you. Some bikes are almost impossible to tune just right. Custom parts need to be made for the carb.

 

(Replying to Scooby)

If I understand your post, your engine runs rich with an aftermarket carb. No identifiable restrictions exist in your airflow. Why not use smaller jets? A handfull of jets costs a fraction of what that flatside set you back.

Most engines profit little from the addition of a larger carb alone; in fact, a carb can be too large, compromising fuel atomization for the displacement of the engine. A big carb complements major modifications, like camming, boring, stroking, porting, and continuous high-rpm operation.

A too-big carb can in fact lower the performance of an engine throughout most if not all its operating range.

Tree Farmer

 

Is an airbox required for your riding....I looked at the picture URL you provided and it does look a little screwy...Anyway that you can ditch the airbox in favor for an open air filter?...Try to get the largest air filter that you can, increased surface area=reduced restriction...other than that it becomes what TreeFarmer alluded to, you've got components that don't work well together for your application....Then ????

 

I know all about over carbing. I bought a 38 PJ Keihin for my LT. Not a good move I could never get it to run right. I was later told that you really need to have some porting done to truly benefit from more carburetion.

RoostKing...

 

Well this carb is a mystery to me! I installed a highflow K&N filter in the airbox and kept the airbox lid off. Now I kind of have the problem of not running rich enough, but not really. What I mean is that the plugs are white and the motor is running hot. I have richened up the jet needle and the main jet, but the plugs still are white. If I go one size larger on the main jet the carb skips during the midrange, but the plugs still show white??? Also, if I enable the accelerator pump, the carb skips in the low & midrange due to too much gas. I would think that if the carb was skipping, that meant too rich, but why are the plugs still white? I am confused!!!

 

I agree with Tree Farmer, a good rule of thumb for carb size (in the muscle car field) is this:

(Displacement * Max RPM) / 3456

For example, lets take a car engine (BTW, this has to be in CI, you'll have to convert CC's into CI.)

350 cubic inches * 6500rpms = 2275000

Take that number and divide by 3456

which equals 658 CFM

So buying a 750CFM carb is doing ABSOLUTELY NOTHING except forcing you to jet down.

Take the time to review www.bombardierds650.com they have a decent article for tuning carbs.

I also plan on posting one on my webpage shortly that I read in a magazine.

Good luck!