jetting for the northwest help is appreciated

[yamahakid1]

i have a bog at 1/8 - 3/4 throttle the cycle shop said to adjust my mains from 300 to 280 to start. but its g etting colder because i live in the northwest and will be goin up to higher elevations for riding. now the needle clip is on the 4th position too. temp has been around 50 - 60 degrees. i think i should go up i on my clip but dont know if i should go down too with the mains. please help

[Banshee~]

List all the mods you have done to your bike, and the elevation and temp. your going to be riding in so we can get you close.

 

Q#14:Why do temperature changes affect my jetting?

A#14:Since the carbs deliver fuel dependent on throttle position, they cannot compensate for changes in air density (only volume).  As air gets colder, the molecules become closer together in a given volume (higher density); cold air contains more oxygen than the same volume of warm air.  More oxygen in a volume of air means that the same jet sizes will not deliver enough fuel to burn the oxygen at the highest efficiency, and what results is a lean condition (just the same as if you decreased a jet size).  On the flip side, as the air gets warmer the molecules are able to expand (lower density); so there's less oxygen in the same volume of air.  Less oxygen in a volume of air means that the same jet sizes will deliver too much fuel, and the net result is that you'll be running rich.  What that all translates to is that colder weather will require jetting larger (usually just the mains), and warmer weather will require jetting smaller.  Going from colder weather to warmer weather will usually result in a bog at WOT (see Q#12), and when this happens you can simply go a size smaller on the mains (and possibly need to adjust the airscrews, see Q#10).  Going from warmer weather to colder weather may or may not give you any indications that you're too lean (it may even run better; the highest performance is on the ragged edge of too lean, however this is also where you can risk damage from overheating rapidly).  Mikuni says that a main jet size is good for approximately a 30 degree F temp range.  While true for a stock machine, as you add mods the temp range that a main jet size works best for may be as little as 20 degrees F (for example: 310 mains for 40-60 degrees F, 300 mains for 60-80 degrees F, etc.).  If there's any doubt (especially if there are any indication of lean jetting; see Q#8), dial in the mains again (see Q#12) or do a plug chop.

 

Q#15:Why do elevation changes affect my jetting?

A#15:In the same way air temperature changes the density of oxygen in a given air volume, so do elevation changes.  As the elevation above sea level (0') increases, there is less oxygen per volume of air (lower density).  Typically you'll need to rejet your mains one size for every 1500'-2000' elevation difference; jet smaller when going to a higher elevation and jet larger for going to a lower elevation (for example: 300 mains at 3000', 320 mains for 0' or sea level IF the temp is the same).  Bear in mind that you'll need to compensate for BOTH temperature AND elevation changes, so going from a hot low elevation to a cold high elevation may net no jetting change.  Much like temp changes, going from a low elevation to a higher one of the same temp will exhibit a bog at WOT because it's rich (dial in the mains-see Q#12); going from a high elevation to a lower one may or may not give you any symptoms of being lean before damage occurs.  While there are other atmospheric factors that can affect jetting (like humidity, barometric pressure, etc.), temperature and elevation changes will have the most drastic affect.

- BANSHEE JETTING FAQ

[yamahakid1]

i have proc circuit pipes new reeds port and polish and no airbox just direct filter clap on to carbs. riding from anywhere from 400-700 ft temp wise anywhere from 40-60 degreezs but this winter will be 20-35 degreez

[2003LimitedBanshee]

Great post Banshee~.. Every banshee owner should familiarize themselves with that page. As you can see from the article, I would consider going up to a 310 main. Actually, a bog at 1/8 - 3/4 throttle could be fixed by simply making an adjustment to your needle. To make certain that you are experiencing a rich bog, while you are in that throttle range pull the choke one click. This should cause a rich condition to worsen, while if you're lean pulling the choke should help the condition. Then make a needle adjustment as necessary.