mid-throttle mixture issue

Hi. I jjust got one of those colortune gizmos and I must say, it's pretty cool to play with. It was very easy to dial in the idle mixture.

White = too lean
Blue = just right
Yellow = rich

But, now I can see that my mid -throttle mixture is off. It was lean (white), so I moved the needle (from the middle) to the lower of the three settings.
Now it's rich (yellow).

First of all - Is there another way to adjust this? (Would the main jet affect mid-range?)
If not - which is preferable? rich or lean?

As always - thanks for the info 8)

hi captain,i think the colour tune gizmos are only for idle adjustment,moving the needle lower weakens the mixture surely,the main jet does affect the mid range , best way is to get the main jet sorted first with plug chops then adjust midrange with the needle or needle jet

chris plant said:

hi captain,i think the colour tune gizmos are only for idle adjustment

Click to expand...

What makes you say that? Have you used one?

swooshdave said:

chris plant said:

hi captain,i think the colour tune gizmos are only for idle adjustment

Click to expand...

What makes you say that? Have you used one?

Click to expand...

hi swoosh ,yes i have used one,to set the idle years ago and it said in the instructions for idle adjustment only(i didnt fancy looking into the glass while the throttle was held fully open anyway lol) maybe the moden ones are different i dont know

hi captain,i think the colour tune gizmos are only for idle adjustment

Click to expand...

I'm sure Chris is correct, and I think the reasons are; the spark is inside the colour tune (was on mine) not in the combustion chamber, and the burn is different when the motor is not under load.

Cash

ludwig said:

If you have the std 3 1/2 slide (cut off ) , change them for nr 3 slides , and
tune from there .

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By slides do you mean the throttle valve (old britts 75 mkIII part #4)? How do I know which ones I have? What is cut off? You mean the end is cut at an angle?

hi captain,the slides are the throttle valves,it should be marked on them what size they are,the cut off (or cutaway is the part of the slide that governs mixture upto 1/4 throttle)the slide is cut at an angle on the atmosphere side of the carb

cash said:

hi captain,i think the colour tune gizmos are only for idle adjustment

Click to expand...

I'm sure Chris is correct, and I think the reasons are; the spark is inside the colour tune (was on mine) not in the combustion chamber, and the burn is different when the motor is not under load.

Cash

Click to expand...

Ya'll need to re-read the instructions. :mrgreen:

This product may be used at a wide range ofengine speeds but should not be used in
an engine under load as overheating and product failure could occur. Take additional
care when using the product on an air cooled engine which has no fan assisted
cooling. On these engines limit the total test duration to 5 minutes and avoid
extended running at high rpm.

Click to expand...

Full throttle
When maximum power is demanded (at full throttle position) it is normal to again have
a slightly richer mixture, at most engine speeds there will be a yellow flame. Engines
with modern electronic engine management systems which have more precise control
would not usually give a yellow flame at full throttle, except at times of rapid
acceleration.

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PDF of Manual

or the older manual like I have:




Set up a little richer and under load you should be fine. This stupid little device got my MG running great when I was a wee lad. Set up a few bikes with it too.

Colortune homepage

swooshdave said:

cash said:

hi captain,i think the colour tune gizmos are only for idle adjustment

Click to expand...

I'm sure Chris is correct, and I think the reasons are; the spark is inside the colour tune (was on mine) not in the combustion chamber, and the burn is different when the motor is not under load.

Cash

Click to expand...

Ya'll need to re-read the instructions. :mrgreen:

This product may be used at a wide range ofengine speeds but should not be used in
an engine under load as overheating and product failure could occur. Take additional
care when using the product on an air cooled engine which has no fan assisted
cooling. On these engines limit the total test duration to 5 minutes and avoid
extended running at high rpm.

Click to expand...

Click to expand...

the only time the engine is not under load is at tickover (idle)so whats the point,all other readings will be false :mrgreen:

I agree with Swooshdave, The instructions clearly state you can use at higher revs, and I know of several folk who have used them sucessfully at other revs, and compared the results to plug chops.
I dont recommend riding at full bore whilst examining the colour, though.
However, I do agree with Chris that the best way to set your main jet is with a plug chop after running at full bore.
You should have the tapered needle in the no 1 position to start.....ie with the clip in the top groove, setting the tapered needle down in the carb furthest (leanest setting).
Once this is right then check at half bore, and adjust the needle position if required.

In my opinion a bit rich is always better than a bit lean, as it will run a bit cooler.

If I do a full bore plug chop would the results be any different with the needle in different positions? I just ask, because it would mean taking them out one more time and moving them to the other setting. Guess I'm feeling lazy. :wink:

Check out this link......

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

Copy into your address line to access....It shows a chart which shows what does what at what revs.
So your needle clip position has no effect at wide open.
Set up at full bore, Then idle, by adjusing the air screw to 1 1/2 turns out to start. Then if pickup and mid range is flat, muck about with the clip position. Move tapered needle up for richer, down for leaner. (If it 'hesitates' when you accellerate from slow, its too rich)
Buyng different slide cutaway numbers is going a bit far, in my opinion. I try to work with what I have got, first, and cheap stuff like main jets.
Have fun! Stu