How the hell do you tune a carburetor!!!

I just don't get it guys. I started at 2.5 turns out on the mixture screw. Made sure the carbs were balanced. Then I put on that frickin' colortune that everyone raves about and I really didn't see any difference from when I had the carbs at 2.5 turns out to 5. It wasn't until the mixture screw was practically unseated that I started to see an orange flame. So then I thought, I'll go old school and use my ear. Nope. Nothing. I didn't see a change in idle as I turned the mixture screws out or anything. What the #$%. Can anybody offer some sort of guidance because this just doesn't make any sense.

 

Sounds like you got an air leak somewhere. Just out of curiosity, though, are you sure you have the air jets in the correct places?

 

These are carbs for an xj900. After going through the carbs it's impossible to mix match jets because they can only screw into their respective places but to answer your question everything is in the right spot.

 

Same here...
Color tune doe's not work for me too and have tested and reinspected just about everything you can think of, just stays blue all of the time, if you had a vacuum leak I would suspect it would be a white color but check anyway.
There are other people with the same experience out there.
There are dyno places for motor cycles out there that will set the CO for you for about 100 bucks or so.

 

It helps if you use th colortune in a fairly dark place. Makes it easier to read the color.
If there is no color change then there is still work to do in the carbs, or there is an air leak somewhere.
Were the fuel levels set using the wet method?

 

How would I find a place that does that.

 

Yes, everything is in check but to your credit, I did check it during the day and it was hard to see. I'm thinking next time I'll throw a blanket over my head to make it dark or I'll just do it at night.

 

You'd think at this day in age someone would've invented a portable oxygen sensor that you could insert into those holes at the bottom of the headers. Is there something like that out there?

 

You could go REAL old school and do it the way Smokey Yunick did it: dark room, holes in the header tubes about 1 1/2 inch from the flange to see the color of the exhaust gas at the port and he would also read the color of the header tubes themselves.

You could also use a thermal couple and do it by temperature

 

Our factory head pipes are double-wall, so you won’t really see the color of the pipes too well

 

Well that is one idea down the toilet; try a thermal couple

 

I'm a little curious about using O2 Sensors for tuning carbs. I know nothing about them except that you have this sensor thing that is positioned so that the exhaust runs over it and gives you a reading of some sort. Could you possibly use it on an inline four by removing the exhaust except the headers and then just placing the sensor thing into the bottom of each header? I know the bike would be a little loud while you use it but it should feasibly work, right. After all, at the base of the headers there are holes for the 02 sensors to connect to anyway. Why not just put the sensor into the pipe itself and start balancing? thoughts

 

I would think that in Oakland there would be a lot of places, Two Wheel Dyno Motorcycle Tune Shops ask them if they have the sniffer probes that screw into the exhaust headers if your bike has them ? then they can check the fuel mixture on each cylinder, if not they can still do a CO test, they just do two cylinders at a time if you have two into one exhaust.

 

Color Tune
Doe's not work on my bike reads blue all the time.
Recheck Valves
Propane test with extended hose to tank, did test twice
New Pilot and Main jets
Wet Sync Floats Three times all within 1 mm of spec
Did test in total darkness with Throttle plate sync tool attached at same time
Had a Older Yamaha Tech who worked on them back in the day look at it and he said my bike runs better then they did off the showroom floor because they ran so... lean back then

 

I actually live in Los Angeles but Oakland is my hometown.

 

There is a reason why gas anaylzers aren't often used in the home shop.
bacharach-fyrite-intech-co-o2-gas-detector-248511.html
Even used gas analyzers fetch obscene money if they are in working order.

 

If you don't see a change in idle or colortune when turning the mixture screws, it means that cylinder is not running on fully on the pilot circuit. That screw adjusts the pilot air circuit, so either it is clogged or being bypassed.

Bypassed you say? Yes. Let's say it's clogged. Then your butterflies will have to open a little bit further to get enough fuel to idle. Then making adjustments to the pilot air circuit will have not effect.

If there's an air leak, again, you are bypassing the pilot air mixture, fully opening it will not put enough fuel into the engine to idle and the butterflies will have to open further. If the gasket to the colortune doesn't seal, it'll have a similar effect (and also reduces compression). Have you checked the compression of the engine?

A final way that you can bypass the idle circuit is by having the carbs be un-balanced. Just because the cylinders pull an even vacuum does not mean they're "balanced." If one butterfly is more closed, it can still pull a vacuum if helped by another cylinder getting more fuel/air, i.e. not being on the pilot circuit, but slightly past it. Intake vacuum is a function of both the restriction (butterfly valves) and the cylinder that is going through its power stroke at the same time as the intake you are measuring. You have to check each of the cylinders with the colortune.

If all of the pilot circuit passages are clear, then you may find one that actually affects the idle and mixture. Opening it up (adding more fuel to the venturi by adding more air through the pilot circuit, confusing I know) should cause the idle to rise.

Remember too that the colortune is ONLY for adjusting the idle circuit. This means that your idle must always be set at the manufacturer's recommended setting. If the idle is higher than that...poof, you're not running on just the pilot circuit, so your adjustments will have no effect. This balance usually takes a few tries, adjusting the pilot mixture, then the sync, and back and forth until everything lines up.

If you like math, note that you are changing 5 independent variables (air mixtures in each pilot circuit, and idle speed) with 8 inputs (each pilot mixture screw, idle screw, and 3 sync screws). There are many combinations that will "seem" right at idle, but it's not until you're close to the right settings that you see meaningful variation with each input independently. Anytime I've doubted the colortune, I later found that the tool worked perfectly and was just telling me that something was still off.

 

I am forever baffled how stuff like this can coexist with the notion that carburetors are "simple" and "straightforward".

 

Back to the drawing board I suppose on the Color Tune issue I sure read about a Lot of others having the same issues ,not a believer yet... and at this point I would not recommend it to anyone I know, my carbs are spotless clean and the idle was at 1100 rpm while setting with the idle sync tool attached and you can tell a difference in idle quality while turning mixture screws, I just don't get it, must be missing something LOL,I would just love to get it to work like it is suppose to work ???

 

Simple in their operations (no feedback other than the slides) but they do require maintenance. The complexity here comes more from having 4 cylinders as opposed to 1 or 2.

I've moved on to fuel injected motorcycles, and let me tell you, it is nice to just turn the key and start it up. However, if I started having trouble with the ignition system, a "good clean" would not cut it, troubleshooting would be a lot harder. My triumph ST1050 had a lot of off idle stumbles and surges. I was looking at ignition maps, throttle position sensor readings, throttle body syncing, connecting to the ODBII to a computer and TuneECU (that was more challenging than you might think). Turned out to just be the MAP sensor hoses were a little loose and that was only used off idle in the fuel map. Simple fix but a lot of troubleshooting for this shade-tree mechanic.

I've taken about a 8 or 9 carbed projects in the last 10 years (most 4 cylinders) that haven't been run in ages and made them run like new. You just have to stick with it.

For either poster having trouble with the colortune, have you done a compression test?