Let's discuss adjusting pilot screws.

Using a colortune kit, I have opened the pilot screws until I got a yellow flame and then closed them until I just got a blue flame--in my case about two turns open.

However, I can close them almost completely and still have a blue flame. I've seen various opinions on this, most usually coming back to reading the plugs. The pilot fuel system is used up to about 1/4 throttle--at least that's what I have read--so the setting would seem to impact performance and mpg a lot at the low end and lower cruising speeds. I've actually marked my throttle grip and seldom get to 1/4 open even when cruising at about 60 mph.

I've seen instructions to close the screws until a red flame shows and then open to the blue flame; open the screws until the yellow flame shows and then close to the blue flame; do the first two and then set the screws in the middle; close until idle drops, open until idle drops, and set in the middle, etc.

I have to admit to some frustration in getting the carbs set correctly and the low mpg I'm getting, and would like some feedback from the pros on this issue. My carbs are clean and stock with new needle valve seats and needles (the metal ones). I have the stock intake (Uni foam filter) and exhaust. The published mpg for the XJ700N is 46, and I seem to be getting about 34, although I haven't actually check since installing the new needles.

 

There is a difference between the whitish/light blue of running lean, and the perfect deep blue, that occurs right before the rich orange color. The amount adjusting range is only a couple of degrees/width of a quarter or so.

I find the orange/rich condition, then slowly lean it out until I get that deep blue. Any further and you get the lean light blue. Even leaving it a little rich (orange) is fine. You just don't want to be lean.

One last note, if the colortune plug seems to be all over the place (not what you are describing yet), it's not the plug, something is wrong in your fuel system. I've doubted my colortune many times, only to find that something else needed to be fixed.

Did you wet set the fuel level and adjust the valves? You'll have trouble fine tuning if you don't. If it's all stock and running well, look for other drains on mpg. Are brakes dragging? Are you leaking fuel? What is your driving style like?

 

I'll second ManBot13. Very difficult to tell where blue goes to white. I like to open the screws until it's orange and then back off to where the orange is almost gone.

Your instructions about turning the screws in until it goes orange applies to motorcycles with an air screw. Doesn't apply to the XJ where the mixture screw behaves like a fuel screw.

 

What bothers me about the color tune is that I can almost close the pilot screw and still not get the yellow/lean flame. The blue seems to be constant once I get it, but I'm going to check at night to see if that makes any difference. As far as I can tell there are no brakes dragging, no leaks, and the valves have been adjusted and the carbs wet set and set at the lower end of the range. The XJ700N manual says 1 mm +/-1 mm, so I'm at 2 mm.

 

Light Blue is lean, yellow/orange is rich. Deep blue is the right color.

 

That means that the system is getting fuel from somewhere else......either the fuel levels are WAY too high (and I think you've verified that they are not), or, the choke system is open slightly..........either the plungers aren't closing fully, or there is damage to the brass plunger valve or the aluminum seat area in the carb body.

A leaky choke system will drain mpg's and it's awfully hard to diagnose. We had the same problem with a 650 Seca that would constantly foul plugs and it took quite a while for us to figure it out, boy was it frustrating!

 

Lean flame isn't yellow - it's blue-white. You need to open the pilot screw to make it rich and get a yellow flame.

 

what do you do if you get all the jets out except ONE pilot jet because its is stripped....

ughhh....

also all the idle screws are stripped.... at a loss here....

sonny

 

You either have to DRILL and E-Z Out those stripped Pilot Screws and Jet -or- buy some Parts Carbs off Ebay and swap-out Bodies until you have a set that you can tune.

ColorTuning:

BLUE is Idle.
A Blue Flame will guarantee you that your Bike will Idle until it runs out of gas.

The trick is to ColorTune the Carbs to perform in the transition from IDLE -to- OFF IDLE.

OFF Idle happens at the moment you open the Throttles and let Fresh Air rush into the Combustion Chambers.
There is some of that Air that IS NOT carrying MAIN JET Supplied Fuel.
That leading rush of Air NEEDS to be Fueled by the Pilot Jet Supply.

That means you must ColorTune --->> BEYOND BLUE.
Idle + Supplementary Richness.

Without Supplementary Richness you don't "Get-out-of-the-hole"
The Bike will Stall or Hesitate.
You need to BLIP the Throttle to get the revs up before you can get going.

The Adjustment isn't very much at all.
Just a Hair Richer than BLUE.

If the Second Hand of a Stop Watch ticking away 1-Minute = 1 Full Turn of the Pilot Screw ...

The Adjustment to be made to provide the Supplementary Richness will be something like 5 -or- 10 Seconds of movement.
A "Tweak"
A nudge.

As you tune for the supplementary richness, ... listen to the Exhaust.
If you have the Plant doing the ... "Pop-eh-tees" Poppity ... hum ... hum ... poppity ... hum, hum, hum, poppity pop.
Tweak the Pilot Mixture Screw ever so slightly until you get the "Poppity's" smoothed-out.

 

Thanks Rick,

Don't really wanna drill out the idle screws but I can't dip these carbs until there out...

Sonny

 

Jet or mixture screws? Two different problems. Drilling out a pilot screw needs to be right at the bottom on page two of your last resort things to try.

Never hurts to let penetrating oil soak on the top of a troublesome mixture screw over night. Try and work it back and forth keeping oil on top.

They can also just be gummed up. In that case carburetor cleaner can help. Spray some up the pilot jet hole and let it work while you have lunch. Not sure you can count on the dip getting in there.

 

I'm pretty sure I can get the pilot jet out, its the idle mixer screws that are completely stripped... They lay too far into the hole for me to get a wrench around them...

Drilling seems like the only option?

Sonny

 

You don't use a wrench for pilot screws. You use a flathead screwdriver.

 

I saved a Cylinder Head by bringing it in to a Regional Technical High School and presenting my problem to the Machine Shop's Faculty Instructor.

They EDM-burned out a broken EZ-Out and Drilled-out several broken Manifold Studs.

You might consider getting some help like that.

 

When I had the choke plungers out they looked perfect. however, if after checking this tank the mpg is still very low, I'll look again. thanks for the suggestion.

 

All it takes is a bent Top Hat on one of those Enrichment Plungers to bleed-up some extra fuel.

Eyeball the Forks that lift the Plungers.
There should be some free play.

 

Another thing to check is the Vacuum Line running fromm the Petc0ck to the Manifold.

If theres a tiny perforation in the Vacuum Membrane ... Gas will bleed from the Petc0ck into the Manifold via the Vacuum Line.

 

The top hats on the plungers are free and loose. I think I will try blocking off the petcock vacuum line to see if that makes any difference. I rebuilt the petcock several months ago, but you never know.

 

When you block-off the Petc0ck Vacuum Line, ... you need to switch the Petc)ck to PRI or the Fuel will be Off.

 

What kind of compression do you have without optimal compression you wont get optimal fuel mileage step one

 

You have to start with the basics

 

when I checked the compression they were all between 135 and 142 if I remember correctly.