colortune question

I just got my new Colortune. I've sync'd the carbs using the differential vacuum method, and it is pretty close. The XJ550 idles great.

My first goal is to adjust the pilot screw air /mixture so that I get bright orange at idle, like this : http://www.youtube.com/watch?v=5BU-5FhX_Qc

Then I would back-off the pilot screw until the orange just disappears at idle. The problem is that I cannot get that bright orange color in the video, no matter how far I back off the pilot screw. By turning in the screw, I can get the bright white color however on one cylinder. I can barely if at all see the blue light, even at dusk.

What do you think?

 

If you can't get to the orange color, then your pilot circuit is still clogged somewhere, somehow....the orange is RICH, the white is LEAN, the blue is IN-BETWEEN and is the "just-right" ideal setting.

Also, it doesn't have to be a "pastel sunset orange" color, the video may be color-enhanced. Orange is orange and indicates rich, Once you're at orange, you start backing off (screwing the mixture screw IN) VERY SLOWLY until you get blue.....the blue area will NOT last long, go too far and you get to white. Maybe the entire "life" of the blue represents a 1/4-turn of the idle mixture screw.

You want to run through the orange>blue>white sequence a couple of times, and then set the screw so it is just barely on the orange side of blue.

Of course, as you set the individual cylinders, you should re-synch after each cylinder. The idl mixture will affect the power output of that cylinder (and hence the vacuum draw of that cylinder), and that now needs to be equalized with the others. Then colortune the next cylinder, re-synch, etc.


After 2-3 complete cycles of the above, you should have a purring little machine on your hands.........

 

When I gun the engine to high rpm, there is a couple flashes of orange right at the beginning of ramping up the rpm, and those flashes look like the video.

Thanks Chacal, I am starting to get the feeling that my pilot circuit is clogged. Months ago when I was starting this project, I didn't know what a pilot circuit was, so I probably did not clean it properly when I "rebuilt" my carbs. Is there a way to ascertain that they are not clogged? When I pull off my carbs for the n-th time here, do I need new hardware, or can I see through the passages?

My original carbs had the choke circuit blocked, so the odds the pilot circuit is blocked goes up. How wide is the pilot circuit, is it as easy to block as the choke circuit?

Thanks for you help.

 

Hey-y-y-y-y Joe, where you going with the CLEANING WIRE in your hand?......da-dum da-da-dumdum, da-dum da-da-dumdum.

Whoops, sorry, it's Jimi Hendrix flashback hour around here.......


The pilot circuit is as small as or smaller than the starter/choke circuit.

Bummer.

If they weren't clogged to some degree or another, we wouldn't be having this conversation!

Because twirling that idle mixture screw would result in changing the colors, like you saw in that video............

 

DOH!

Is the pilot circuit the same as the enrichment circuit? Timefor me to do some searching and learning.

 

NO!

The pilot circuit has the PILOT FUEL JET at one end, the PILOT AIR jet at the other end, and uses the PILOT MIXTURE SCREW (oftentimes called the IDLE MIXTURE SCREW, but it's proper name is really a PILOT CIRCUIT MIXTURE SCREW) to regulate and adjust the flow through the pilot circuit. The little screws that you twiddle when you're playing with th Colortune plug is this pilot circuit mixture screw.


The starter/choke/enrichment circuit starts down int he bottom of the fuel bowl with that non-removable STARTER JET (that gets plugged up in the bowl), continues up the brass suction tube that hands down fom the bottom of the carb body, and goes up through the starter/choke/enrichment brass PLUNGER VALVE that is actuated by the "finger bracket" which is connected to the choke CABLE that runs to the left side control switch LEVER.

 

Pilot circuit="low speed" circuit.

Enrichment circuit="choke" but it's not it just thinks it acts like one.

The Mikuni pilot circuit is a bit complex, comprised of quite a few oddly angled components, and you can't effectively "see through" all of its passages. Blowing carb cleaner and air through and poking with tiny wires is the only way to get them truly clean.

 

My enrichment circuit was completely clogged, but I replaced the bowls, and now they work exceedingly well. Durng my "rebuild" I did spray carb cleaner through every hole and they all appeared clean. However, if the pilot circuit is smaller in bore than the enrichment circuit (as Chacal states), I certainly could not have sprayed carb cleaner through it, and especially if they are circuitous. I mean, the carb cleaner poured out, it was probably the main jet I cleaned.

I looked at the Hayes manual, and it's not too clear where I am supposed to poke wires in. And poking wires is going to make me nervous, I don't want to ruin the passages. I'll take some photos and ask y'all questions.

One other thing... I was having jerking motions and backfirey pops at high RPM, so does that mean my main jets are having a problem? Or does it mean that my float levels are bad? Or could it be my pilot circuit would give me these symptoms.

Thanks for the advice.

 

I would say A or B.
Cause your running out of fuel.

 

I would suspect float levels too based on your symptoms.

 

OK, I have the carbs off and needing to understand all the fuel circuits involved. On the attached picture, what are the jets/ports labelled A,B, and C?

 

a = pilot fuel jet, part of the pilot fuel circuit

b = main jet, also called a power valve or emulsion tube, part of the main fuel circuit

c = should be a blind hole, leads nowhere and to nothing.

 

What is D,E,F?

I think I need to poke the wire in these. D and E may be connected with a circuit. F appears to be connected to a circuit that bypasses the butterfly valve to another port right behind it? Not sure.

(D was clogged. Also, previous owner did not have any washers on the pilot screw, glad I bought some!)

 

Actually, F is three tiny holes.

 

F would be the enrichment fuel hole. D is the Idle Mixture Fuel Hole. Not sure exactly what e does. Those are Makuni carbs and they are different than Hatachis

 

So I just used my color tune yesterday for the first time. The bike, to me was running great But I couldn't see any color on number 1, then I tried 2, could see the blue/orange .. then 3, and 4. Back to 1. still couldn't see a color.... whats wrong??? I noticed the plug was like new.... must be a little lean .... thought I would check the float bowl drain ... nothing, nodda, dry as popcorn fart! Number 1 was not even firing! even though it seemed to be running so smooth ... duh ... Anyway, it's all good now ... having 25% more power is almost scary .. this bike hauls butt.
Just adding this for your reading entertainment!

 

Thanks! Actually, E is three tiny holes, not F.

 

Hope this helps for the next guy. Performing a float level adjustment on the balcony of an apartment...

Here are pics of my float level setup. Basically, I sandwiched the carb assembly between two angle brackets and secured them tightly with duct tape. Clamps and shims were used to perfectly level the apparatus as described in Chacal's classic: CHURCH OF THE CLEAN

 

You are a creative sucka, Joe!

Bet the neighbors love you........

 

Mikuni carbs do not have a nipple to attach the the fuel level monitor tubing, and you can't buy any, so you have fashion one. My first attempt was a whittled down pen cap around aquarium tubing --- while it did work OK, it did seal very well, and popped out very easily.

My second attempt was an O-ring around the (reddish) tubing. The O-ring was pressed into place in the fuel port with brass tubing that was a little bigger than the plastic tuning.

Below are pictures of the materials. HTH the next guy.

 

Below is the result of measuring the fuel level for cyl 1. The two photos below are enhanced with green to emphasize the meniscus and a line where the bottom of the meniscus SHOULD be (just to double check, is this line in the right place?).

This looks like cylinder 1 is running very rich?

 

Here is cylinder two, again with green as enhancement of the meniscus. I think the green line I drew for picture one is too low. It should be 2 mm from that top piece. Is this green horizontal line better placed? Thanks.

Even so, this cylinder is running rich too.

 

Here is the third cylinder, it looks very rich, no?

 

Here is cylinder 4. I didn't enhance the meniscus, you should be able to see it. Rich also, right!

Am I doing everything correctly? My job is to bend those tangs such that the meniscus comes down to the green horizontal lines in all the pictures, right?

I want to make sure I understand everything before proceeding... Thanks for your advice!

 

Those are all High

Look at the Pic. You want meniscus of the fluid ... the lowest part of the U that indicates the height ... to be Level with the Bottom of the Washer between the Screw Head and Float Bowl.

See Factory Manual Shot Below::

 

Rick is correct........but Joe, also note in that diagram that you are supposed to pull the tube around to the SIDE of the carb body, so that the tube is held vertical along the front-to-back centerline of the carb body (and bowl)......this puts the tube about in line with the main fuel jet in the bowl, which is really the "fuel level" that matters...........

 

Gracias, amigos! I will remeasure in the proper position. I think I got it under control. But Rick, just checking: that drawing was for some other carb, right? My Mikuni's are supposed to be 2.0 mm +/- 1.0mm below the carb body mixing edge, right? (Not 5.0mm as it says in the drawing.)

Thank you all. The finish line is in sight!

 

Forget the "Numbers" for a Minute and L@@K at the Drawing.

You NEED the Float Level within a limited area.
If you have the Level at the Bottom of Screw ... "Acceptable"
Below the Bottom of that Screw ... NOT "Acceptable"

The TOO HIGH Level is ABOVE the Washer.
In other words ... Beyond High is Real Bad and can Flood you out.
The Middle area ... Washer down to the Bottom of the Screw Head ... OK
Below the Bottom of the Screw Head will mess you up when you are really rolling-on the power.

{The Numbers in the shot at Mikuni - 900}
The Levels shown are GOOD!

 

Thanks Rick, I now have all levels perfectly in the Green zone. Got really lucky and only had to do three iterations.

 

I got the carbs back on my bike, sync'd 'em, and the high rpm end is very nice now, it pulls strong all the way up the rpms... the float levels were the problem. At least I fixed that.

The throttle responds quickly and settles quickly back to idle, BUT I am having idle problems now, whereas I did not before the I cleaned out the pilot circuit clean yesterday. The idle is uneven and "bumpy" now. I feels like it is going to stall, unless it is at about 1800 rpm.

To check whether the pilot circuit is blocked, I backed the pilot screws out 3 turns, and adjusted the main idle to low rpm but sustainable. If I turned in each pilot screw, it would stall the bike. So it looks like the circuits are not blocked, and they better not be, I just cleaned them.

I attached the Colortune, but no matter how far I backed out any of the pilot screws, I could NOT get a yellow color. The Colortune looked the same for all cylinders. Sparks were strong in all cylinders.

To show that the Colortune was not bad, I turned on the choke (and adjusted the idle to low but sustainable) until I just got a strong constant yellow. Colortune OK. I then turned in the pilot screw in until the yellow went away. Pilot screws OK.

(I wish it would go from yellow-> blue when the choke is off!)

Any ideas? To me it seems that pilot circuits are clear, but they are not getting enough gas, somehow. I should be able to go from yellow->blue and back on the Colortune by turning the pilot screws in and out without the choke on, right?

Thanks for any advice.

 

Inventive crew here.

To state the obvious If you can get it to go rich with the choke then you must not be getting enough gas through the Pilot jet. You didn't by chance reverse the Pilot and main air jets in the top?

Also how about the Tiny enrichment jets int eh bottom of the bowls? Sounds like you are getting gas through them but they have to be squeeky clean too.

 

Necessity is the mother of invention... or is it desperation is a mother..?

The enrichment jets are for choke, and they are squeaky clean. That circuit is working well AFAIK.

Yes, the conclusion is inescapable: the pilot circuit is not working yet. I should be able to turn the Colortune yellow with the pilot screw only (no choke).

Thank you Bill for that great idea about mixing up jets by mistake. I would not put anything past the previous owner. Could you tell me which two jets you think may be swapped in the image below? Note that one jet is not labelled, so I put a red question mark next to it.

Previous owner mixing up jets would be consistent with the fact that ALL the carbs are behaving the same: consistently lean, unable to colortune to orange.

What is the best way to ascertain that the proper jets are in place? Are they marked or do I need to measure them? What is the best way to measure them?

If I check the jets and find that they are OK, then there must be something wrong with the circuits. On the image below I marked the fuel path with red, the air part with green. If I understand carb theory at all, it seems that the air is sucked in through the main air jet, which sucks up the fuel and pushes it to the pilot outlets (which I know are clean).

Since the bike runs great at high rpm (and all exhaust pipes very hot), the main air jet is probably OK. That leaves the other air circuit that sucks in at the red question mark which in turn comes from that subcompartment at the top. (What is that diaphragm for anyways?)

In the image, I have these two green streams of air merging immediately before hitting the fuel path (red) in the pilot circuit). I am not sure whether they do or not, the diagram is ambiguous. If they do not, it would make sense that the jet marked with the red question mark, and the pilot jet could be swapped.

Should I expect to get a wire all the way through the pilot fuel (red) path? Has anyone else ever gotten a wire all the way through? I would hate to fatigue it and it would break off in there. Do I need push a wire through the air part (green). Is getting a stream of carb cleaner good enough?


Thank you VERY VERY much.

Joe

 

Ahh yes, the diaphragm. In-rushing intake air creates a "vacuum" (actually a 'lower pressure' condition) above the diaphragm which responds by lifting the slide/needle and allowing fuel to flow via the "needle jet." This "passive" actuation of the slide via the diapragm (or piston on the old SU carbs on British cars) is what makes a CV carb a CV carb. The bottom line is the carbs don't trust us humans with anything as important as slide position, all we get to do is open the butterflies and the carb takes over and does the rest for us. Provided it's working correctly.

 

Fitz, you got me curious and I found a nice powerpoint on carb theory:

http://people.morrisville.edu/~crovelp/ ... Theory.ppt

 

Joe my mistake you have a550 - (someday I'll learn to read the references) on the Mitsubishi carbs the main and pilot air jets are on top by your ? and are easily swapped. In fact haynes shows the wrong positions.

Carb cleaner should be good but make sure you get a good stream - debris can let if flow but not fully.

Your right about the choke - I should have been more specific I threw that in to say you are getting flow (evident from colortune) but while you have them apart it is good to get them very clean. Sounds like you did.

Are your slides working well (do they pass the clunk test?) I'm not sure if the main contributes to the idle but if all the path ways are clear I can't figure out why you you are having those issues.

 

Fitz --- if one blows into that little oval compartment at the top of the intake, the plunger goes up... cool.

Bill --- Slides are doing well, all pass the clunk test from your video. They show no signs of wear. All jets are of different size, so can't get 'em mixed up.

BUT I think this grasshopper figured it out. All four of my pilot jets were at least partially clogged, like you mentioned might be. I took them out and could not see light through them, so cleaned them out with a whisker from a brush. The jet size is about a human hair, really, very easily clogged.

Now to put these puppies on the bike and find out...

 

That could do it for sure. let us know...

 

wOO HOO!!!! My rocketship "Zoso" is a frikkin' BAT OUT OF HELL.

All carbs colortune-color controllable with pilot screw now!

Moral of the story -- SEE LIGHT thru the jets, not just squirt carb cleaner thru.

I stayed true to the CHURCH OF THE CLEAN. I may have been slow, but I did no HARM to Zoso. The scales have been lifted from my eyes!!

Woo hoo! Of to get Zoso inspected by the great state of Texas, then BEYOND!

 

D is where the pilot screw needle end will protrude into the carb throat when the screw is turned all the way in. By adjusting this screw in and out, the amount of needle "blocking" the hole can be set at different levels such that a different amount of additional fuel is added to the default fuel flow coming out of E. This adjusts the idle mixture lean or rich.

 

And when you get the Pilot Mixture Screws adjusted correctly the TOTAL amount of movement for Fine Tuning is shown in the accompanying graph.

You Tune the Pilot Mixture Screw to be Slightly RICH.
The Slight Enrichment is: Supplemental Richness.
Supplemental Richness is NEEDED for:
>>Keeping the Mixture Cool Burning
>>Providing FUEL to Maintain Ignitions for the BRIEF (Two eye-blinks) Duration for when the Throttles are Opened --> Off Idle --> To Main Jet Flow.

The Graph illustrates: One Quarter Turn --> 0 -to 90 Degrees.
The ORANGE Section is Fine Tuning.

Fine Tuning will be: LEAN for Rapid Acceleration and Engine Braking or
RICH for Cool running, Smoother Application of Power, Heavier Loads, Highway Cruising and Engine Coasting.