I just got my HMF Bill Balance carbon slip on for my 04 400 and the jetting must be way off. They recommend a 152, with a 42 pilot. It has the stock 38mm pumper Keihn carb on it and, I have a K&N with airbox lid off, stock header pipe and a Rev Max CDI, it will only run with the choke pulled on, and even pops with it halfway on. I have dinked with the fuel screw from 1.5 to 3.5 turns with no avail. Needle is in the middle position as well. Also what is the deal with the nozzle the main jet screws into, it is adjustable? Where do it set that thing at as I haven't touched it yet. JOhn

 

The air-mixture screw has nothing to do with it at this point. Sounds like your needle is too low. Raise the needle one notch and try it, then two if need be. If that doesn't work, go back to your jets. Sometimes a dealer reccomends certain size jets but you might be in a different part of the country(different elevations).

 

If its anyware near as cold out your way as around here your not going to get away with the needle that low or the 152 main (you do have a keihin main correct?)

The air is just too dense when the temps are this low, and I have had problems with mine (same carb, but more mods and larger bore) running a 178 main in temps like this. Pretty much same problem with needing to choke her up etc.

Try the needle, and pick up a couple jet sizes larger just in case you need them. I would say up to around 165 or 168 should cover you.

Also these are keihin numbers and they would not be the same if you have swapped over to dyno or ?

 

Well, raised the needle all the way, and put in a 180 keihn jet, running great now. BTW it does not have an air mix screw it is a fuel mix screw. Well now I have to try the 450 r carb I bought on ebay. LOL thanks fellas, John

 

Glad to hear its running.

Just remember that if for some reason you dont install the new carb your going to have to jet down again when it warms up.

 

Settled in to a 165 main, thanks for the heads up with the needle, it is really running good now, I am not too sure if I am going to put the Cam and carb in just yet as it is so much fun to ride as it is now.

 

I know what you mean as just the typical aftermarket and exhaust mods make a big difference over bone stock, and especially when jetted correctly.

There are a bunch of old threads around detailing just about every mod available on this quad so take a look around and see what info you find helpfull (or I can point you in the general direction etc), but from the point your at now it normally takes a couple of well chosen mods to create a similar increase in power.

An example is that just going to a larger profile cam will not do it, but it will if you do a larger bore (say 416 etc) and higher comp piston at the same time.

There are also many little tricks you can use to gain some extra hp etc, and others that can help put the increase in the area or rpm range that works best with your style of riding, but I wouldnt recomend going full out (big bores, strokers, valves, etc etc etc) like many have in the past because now that the 450's have been out a while offering not only increased engine performance but also making even higher hp engines possible and are being sold at relatively inexpensive prices used (not as good as the 400 though lol) its just not worth the investment anymore.

Still you would see a good improvement with just benefits of a cleaned up cyl and higher compression combined with a larger cam (stage 2 is good std etc) and your current mods combined would make a really nice combo without getting into the much more expensive mods.

I know I wouldnt do it again today like I had in the past, but back then there wasnt any other real options.