I have an 03 400 with snorkels and the exhaust mod. I put a jet kit and adjusted the needle and it still doesn't run right. Throttle response is slow and top speed is slow. Would a 500 h.o carb eork

 

If it ran ok before the mods, should still be able to tune it. The trick, imho, is to start, getting it to idle smoothly and start, then tune the midrange by maybe shimming the jet needle to get mid range to run smoothly. Lastly get a bunch of main jets, stock to maybe 3 or 4 sizes fatter. The main jet that gives you the highest top speed is probably the correct one. I had 2 Cats, a 500 and a 400, both ran Keihin CVK 34 carburetors.I got both to run much better with Dynojet kits. The 500 had a race cam, K&N , gutted muffler. I got the 500 to run 64 mph with heavy 30" Mudzillas with those mods, the 400, gutted muffler, Dynojet, K&N ran just under 60 with tuning. I don't think you have done anything radical, so only a bit fatter than stock settings.

 

Hydrex is right that you should be able to tune it. But if you really want to change carbs, first of all, what does it have now? If it's the same 32mm Mikuni the 500s had before they were H.O.s, it would be possible to put the larger 40mm carb on. But you would need an adapter to make it fit the smaller opening of the air box. Or the air box off a 500 H.O. Is it running too rich? If so and you can't tune it, your snorkels which already aren't giving it enough air, would need to be replaced with bigger ones. The opening of a 40mm carb is a 56% larger area than on a 32mm carb and it needs a lot more more air flow. Proper tuning of your current carb is the easy answer.

 

Take the carburetor off and clean again, check that there is no restriction in gas line (pull of line at carb, let run into a clean container, should be a nice flow, also confirm that float is set correctly. Just think, if it was not too rich or too lean before, it only needs a wee bit more gas, mostly at wot. Do a "plug chop" , easy way to check if too rich or too lean. You could also check if covering part of air filter, makes it run better or worse.