I've been messing with it a bit now and, i'm getting more lost. When I had 175/172.5 mains and, the Dynojet needles on the 4th clip it was burbly and, wanted to die off the bottom, I'd Wheelie a bit in 1st bring it down to shift and, it would seemingly drown out. My Builder suggested going to the 3rd clip on the needle and, this helped but, it didn't seem to perform too what it should. (I beat my buddies piped YFZ450 by 1 bike and, he is not to good). I pulled the plug and, it was black. My builder then came up with a corrected Elevation for my area due to our heavy humidity and, said to try 162.5/160 and, go back to the stock needle on the 3rd clip along with take the air screw in from 3 out to 2 out. This made it idle better and, was pretty snappy from bottom but, everything else is weird. Now when going throught the gears it revs pretty well (not great) but wants to die after each shift and, crackles a bit. Also (this was at 10:30 at night and it was only 50* out) my pipes were glowing as red as a cherry when i only made a short burst around the block to test it.

I think i went from rich to real lean but i'm a newbie to tuning and, can't tell if it is rich or, lean. Or a combo of both ie.. Rich on bottom and, lean on top or vise versa.

I'm lost and, scared to do harm to my big dollar engine. Please Help!!!!!!!!!!!!!!!

 

hey capt. i havent seen headpipe yet that doesent glow red at night they put out alot of heat. anyway to start, piolt jets are mainly used from idle to 1/4 throtle and main jets are from 1/4 to wide open as a rule, they do work together inbetween but not on each end. so if your rich on the bottom change your piolts, if your lean on the top go with bigger mains. As for the needle that is where it gets tricky, going up and down on the clip allows the fuel to flow faster from the mains not always more fuel cuz the mains meter how much fuel will flow up the needle, so if you are a little fat to start and move the clip down your motor will get fuel supplied faster, if you go up on the needle clip it will slow the flow of fuel and alow your motor to keep up with the fuel delivery. that is a very basic and simple explination of how it works, it is actually more complex than that once you throw in needle jets and air fuel atomization but that is an easy way to look at it while trying to understand what jet/needle changes to make. hope this helps

 

What mods to your air box?
You should be around 190 on the mains
25 pilots
about 2 3/4 turns on the mix screws
Start with the clip in the middle on the needles
ADJUST THE FLOAT LEVEL!!! Very important!

This is the best way.

The best thing to do is check it before you take it apart, with a piece of clear tubing. You can get the tubing at a hardware store for 20 cents, 1/8" clear tubing.

Thu September 05, 2002 3:11 AM



The quick & easy way to check float levels is to use a clear tube that fits the dump hole on the bottom of the carbs. You'll need at least one foot of tubing. Don't worry about an exact fit, the tubing can be a little bigger which will cause some of the gas to leak out but gravity is forgiving and is constant! You can get the tubing from your Yamaha dealer for a few bucks. Remove the stock dump hole tubing, put the new tubing on there & then bend up the other end and run it along side of the carb with the open end facing up. Then open the drain screw next to where the tube is connected & the level of gas in the tube should fill up & be level with or slightly above the bottom/top half of the carb's mating surface. If not, you'll need to adjust the float levels. A sign that the float levels are too high is if the stock drain tubes leak gas while your riding, you'll smell it for sure.
I just pop the carbs on the boots and set the tank on the frame and hook up the hose to check it again, you may have to take it back off once or twice to get it perfect. I also measure the amount that it is off and then take it apart, measure the float height and then bend the tab enough to raise or lower the float the amount that it was off. If that makes any sense.

 

My airbox is dremeled out so there is no ridges in it and, has the ProFlow adapter (sooory SIX SIX, you made Yours a few weeks after i got it) w/ K&N Filter with outwear cover and, no lid. It seemed Rich w/ 175/172.5 Mikuni Jets and, the plug was black. 190/195 would be worse right? I don't know, It coulda been lean on top and, rich everywhere else? I'm Clueless.

I noticed none of you are using half sizes, like 175/172.5 Mikuni's. Should I try staggering it more? ie.. 175/170? 170/165?

Please give some sugestions, I'm doomed. My luck always sucks and this is no worse for wear!

Could the 110 Octane i'm using make it more picky?

I just couldn't leave well enough alone = It ran like a champ just piped and, jetted (winter or, summer ). I'm a glutton for punishment! Looks like Memorial Weekend at the Dunes for the 686 Christening is out the window! DANG-IT!!!!!!!!!!!!!!!!!!!!

This BLOWS that all the tuners and, people who know performance are in the Southwest where they don't know what humidity is and, have 1,000,000's of people for testing and, trial an error! The MIDWEST sucks (well Illinois at Least)!!

Now i'm really getting pissed!

 

humidity wont make a huge difference to air density mainly tempature and altitude are the main factors, the probs you are describing are purley jeting sizes arent matched up just right, and like sixsixT said make sure your float level is right.

 

just get some differnt jets and start testing them youll be so happy once it is working correclty

 

This is surprizing.. I thought their were more 686 owners out there that would be willing to chime in for help?

Could maybe some of you call your builder and, ask them how you jet yours for Chicago Area. Maybe tell em your going to a race here or to visit friends? Or, you could say Silver Lakes Michigan Dunes Area - Might be more familiar?

Possibly, they'd have a good starting guess guess for my area? Or, even better they have built one for here, trouble shot this before and, know exactly what to run? But, not w/ my luck.

 

I'm my own builder, so cant help that way.

 

give sparks racing a call or trinity racing they have always been really helpful to me

 

also i understand sixsixt knows what he is doing with carbs