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Colortune??? 1988 150 hp

C

Cut2Short

Member
Anyone ever heard of a carburetor tuning tool called Colortune??

I’ve been really struggling on getting my 1988 Mercury 150hp XR4 to run the way it’s designed, while I’m still waiting for the carb kits to get delivered, I was talking to a friend who has a device called a Colortune. Supposedly, it has a glass sparkpug unit that you can see the different combustion colors (yellow being rich and bunsen burner blue being balanced, and white blue being lean) and fine tune the air/fuel mixture ratio by adjusting the various jets. I was hoping to find a little advice on how this tool worked and maybe the best way to use the tool. The literature says to do all of the testing at idle, but I was thinking of keeping it on the trailer, putting the motor in the water, placing it in gear and try running it through the various throttle positions. It comes with a little black tube with a mirror to enable you to see the clear sparkplug from a different angle than straight on, so I should be able to work off of the back deck of the boat.

Any shared experience would be greatly appreciated. Mostly, does it work.
Steve
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Re: Colortune???

I have heard of that "contraption".

You get a (sparkplug) that basically has a glass eye in it. You get the one that fits your thread pattern etc and install it in place of one of your plugs.

Then, with the motor "running", you look at the colour of the flame in the cylinder while trying to adjust the jets on your carb (ya right).

Of course, that assumes you have adjustable jets.

On your particular model you have "non-adjustable" jets.

There is an idle air, a backdraft vent, a progression (2 per carb) and a main jet - so 5 fixed jets per carb (or 15 total on your set-up).

Your only option would be to buy a handful of jets each about 1/100th of an inch bigger or smaller than each other and replace each one, in turn, before checking the flame colour again.

Not really practical on this application....
 
Re: Colortune???

Hi

You can buy colortune in the UK and it is for adjusting the fuel/air mixture to ensure you are not burning lean or rich.

I always thought you adjusted the mixture with the mixture screw and not changing jets. (except for changing jets for altitude)


I am not a new user, I forgot my log in details
 
Re: Colortune???

Sorry, 6 jets per carb - there is two main jets as well... (getting old and forgetting stuff) :)
 
Re: Colortune???

Some carbs are "factory" set and others have adjustable needle valves.

Most of them with fixed jets try to balance the amount of air in the carb and the gas flow is (fixed).

With adjustable jets, you are trying to control the amount of fuel in the ratio.

So two totally different concepts.

With the carbs used on the these models (XR2, XR4, XR6) you have 3, dual throat fixed jet carbs with air trims (factory set as well) - but do have an idle mix adjustment.

The air idle (bleed) jet regulates how much air the carb uses to balance the idle mixture which actually fuels the motor up into the 2000-3000 rpm range. The (adjustable) idle mix screws will allow the user to alter the fuel mix.

The backdraft jet reduces the air pressure in the carb bowl at mid-range rpms to improve fuel economy.

The progression jets work in conjuntion with the air idle jets to supply the demands as the rpms increase until the main jet takes over all the fuel supply requirements.

Because of the above simply going to a different size air idle jet can cause a significant imbalance unless the progression jets are matched to the change as well.

And just to keep everything really interesting, not all of the carbs on this motor run the same size jets for each cylinder - some guy with a bunch of letters after his name figured out what size jets go where for each cylinder to keep the whole thing balanced properly.

Which led me to my earlier comment about grabbing a handful of jets because you could spend hundreds of hours trying to achieve a workable balance if you vary from the established configuration...
 
Re: Colortune???

my apologies Graham,

got it now, as I am not an outboard mechanic, I wrongly assumed that a jet was a fixed size and the colortune was good for adjusting the mixture by adjusting the mixture screw.
cheers

James
 
Re: Colortune???

You could use it on this model to tweak the idle mixture, I'm just not sure of the overall benefit.

Say you "idle" the motor a 700-800 rpms and use this thing to view the flame colour and tweak the (adjustable) idle screw.

Ok, so you get the nice blue flame like you are supposed to.

Now you increase the rpms to 1600 or so. What if the flame isn't nice and blue anymore?

At that point if you fiddle with the adjustment again you have "knocked it out" for lower rpms.

Logically, you would leave it alone and try a different size air idle valve.

Then once you have found the correct one for that rpm, you go up another few hundred rpms and start swapping out the progression jets.

It might be valuable if you were say building the engine for racing and you only cared about "the perfect burn" at max rpm.

You could rejet and tune to that rpm range, or alternately, if it was a commercial boat "trolling" all the time.

But for average use on a model with mostly fixed jets, I just don't see the benefit.

However, hooking one up to a properly tuned motor would give you an idea of how well the motors designer did when they figured out all the jetting for the carbs...
 
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