could be a dumb question but with all the reading i have done on this site i have read a lot about rejetting - now i have read where people have gone to a K&N filter and they had to rejet - is that for all higher flowing air filters?? got a uni and thought i would ask before i put it on.

 

anytime you change the amount of air going into the engine you have to compensate by adding fuel

 

more air, more fuel, got that but do you have to re jet or can you just adjust the carb? more air means it should run to lean so just rich'n it back up, right?

 

You might be able to just adjust the needle in your carb by putting the clip lower on the needle riching up the fuel mixture.

 

So going from a OEM style foam filter to a UNI foam filter i would have to rejet?? was thinking like medeff and would change the mixture at the carb.

 

its possible to even out the a/f without having to rejet. just takes a little more time "fiddlin" with it

 

YES!!! you can change the mixture at the carb you just have to adjust you main jet needle. move the clip down and it will richen up the fuel mixture.

 

Replacing a stock foam filter with another brand of foam filter shouldnt change things much at all.

Keep an eye out for drivability issues, and if you experience any, then youll need to rejet.

The mixture screw will only effect the idle mixture. The needle will only effect the mid throttle, and for wide open, the main jet, which isnt adjustable, is the controlling factor.

Heres a good article on jetting, and it lists the drivability symptoms of incorrect jetting.
jetting

This is part of that article.

A lean condition is the end result of too little fuel and too much air. Slightly lean conditions create drivability problems. Worst-case scenario: Lean conditions can and do destroy engines. Holes in the pistons, burnt valves and trashed main bearings are the direct result of lean mixtures.

Rich mixtures are the end result of too much fuel and too little air. Rich mixtures waste fuel, contribute to carbon buildup and pollute the air.

Typical Lean Conditions:

- Poor acceleration; the engine feels flat.

- The engine won't respond when the throttle is snapped open, but it picks up speed as the throttle is closed. (A too-large main jet also mimics this symptom.)

- The engine runs hot, knocks, pings and overheats.

- The engine surges or hunts when cruising at part-throttle.

- Popping or spitting through the carb occurs when the throttle is opened. Or popping and spitting occurs through the pipe on deceleration with a closed throttle.

- The engine runs better in warm weather, worse in cool.

- Performance gets worse when the air filter is removed.

Typical Rich Conditions

- Engine acceleration is flat and uneven and loses that "crisp" feel.

- The engine "eight-strokes" as it loads up and skips combustion cycles.

- The engine's idle is rough or lumpy, and the engine won't return to idle without "blipping" the throttle.

- The throttle needs to be open continuously to maintain acceleration.

- Black, sooty plugs, a sooty exhaust pipe and black smoke from the tailpipe that stinks of unburned fuel.

- Poor fuel economy.

- The engine works better when cold. Performance falls off as it warms up or the ambient temperature rises.

- Engine performance improves when the air cleaner is removed.

 

hondabuster is the only one with the correct responce. And the link he gave for getting is the one I always give out also.
Honda jets there trikes Lean from the factory, if you add an airfilter bumping up the main jet about 2 sizes from the very begining is a good start. Most rebuild kits you will buy will only come with a bigger main jet than the stock one.
If you need a jet there is a good chance I have a couple laying in the garage

 

Since a person can never have too much carb info;

Carburetor Theory 101

If you're good at reading spark plugs I have always found this very helpful, it is part of the above link.

Except you might have to do it a little different with a thumb throttle, but you'll get the idea.

While jetting carburetors, place a piece of tape on the throttle housing. Place another piece of tape on the throttle grip and draw a line (while the throttle is at idle) straight across from one piece of tape to the other. When these two lines are lined up, the engine will be idling. Now open the throttle to full throttle and draw another line directly across from it on the throttle housing. At this point, there should be two lines on the throttle housing, and one on the throttle grip. Now find the half-way point between both of the lines on the throttle housing. Make a mark and this will show when the throttle is at half throttle. Divide the spaces up even again until idle, 1/4, 1/2, 3/4, and full throttle positions are known. These lines will be used to quickly find the exact throttle opening while jetting.

Clean the air filter and warm the bike up. Accelerate through the gears until the throttle is at full throttle (a slight uphill is the best place for this). After a few seconds of full throttle running, quickly pull in the clutch and stop the engine (Do not allow the engine to idle or coast to a stop). Remove the spark plug and look at its color. It should be a light tan color (for more info on reading spark plugs click here). If it's white, the air/fuel mixture is too lean and a bigger main jet will have to be installed. If it's black or dark brown, the air/fuel mixture is too rich and a smaller main jet will have to be installed. While changing jets, change them one size at a time, test run after each change, and look at the plug color after each run.

After the main jet has been set, run the bike at half throttle and check the plug color. If it's white, lower the clip on the jet needle to richen the air/fuel mixture. If it's dark brown or black, raise the clip to lean the air/fuel mixture.

The pilot circuit can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. If the screw is in the back of the carburetor, screwing it out will lean the mixture while screwing it in will richen it. If the adjustment screw is in the front of the carburetor, it will be the opposite. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs.

Jeff