Anybody here use Colortune?

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Neil Bardsley
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Re: Anybody here use Colortune?

#16 Post by Neil Bardsley »

David Jones wrote:I used a colourtune many years ago to tune BMC engines in the UK before I got wise and switched to a Porsche. I got lazy and instead of writing what I remember I did at the time I stole from the internet. Thhis is pretty much how I did it all those years ago. Paraphrasing the words of the Mythbusters. "Don't try this at home, we are what you call experts". I would add to the write up that it is probably pointless to do this on each cylinder unless you have a lot of jets and want to end up with different jetting for each cylinder.

The Colortune, then, is indicating at the colour transition
points the mixture strength of the ingoing charge. Maximum
power occurs when the fuel/air ratio is between about 12,5 and
13,5:1. The exact point varies from engine to engine, but
most cast iron tuned production engines seem to be best around
12,8:1. The best economy is achieved on weaker mixtures than
that giving maximum power, and fuel/air ratios between 14 and
16:1 seem to be the easiest on the pocket.

To set up the mixture in the manner about to be described you
will need an accomplice. The first and essential step is to
part the car in some place which is poorly lit, so that you
can see the combustion colours. Jack up the driving wheels of
the car until they are just clear of the ground and in the
interest of safety, securly blockthe car so that it cannot
move under any circumstances.

At this point, warm up the engine, then remove a spark plug and
replace it with a Colortune. Set up the mixture so that you
have a fuel/air ratio of about 12 to 12,5:1 (orange/blue) at
normal tickover revs. If you have multiple carbs you will
have to do this for each cylinder or set of cylinders having a
carb.

Next, get your accomplice to put the car into gear, usually
third gear is best, and increase the throttle opening but at
the same time put on the brake. (Continue opening the
throttle and increasing breaking pressure until your
accomplice ends up with the throttle wide open and the revs
pulled down by braking to 2000 rpm). You can now look ath the
Colourtune and at this point it will reveal what the fuel/air
ratio is under the prevailing conditions.

It can then be noted, preferebly by colour rather than
reference to its fuel/air ratio. After this, let the brakes
cool for a few minutes, then repeat the procedure at 3000 rpm
then at 4000 rpm and finally at 5000 rpm, stopping to let the
brakes cool between each run.

As far as brake overheating is concerned, it should not take
more than fifteen seconds to ascertain the mixture ratio at
each rpm interval, so they will be well within their capacity.

Once you have an indication of the state of affairs of the
fuel/air ratio up the rev range to 5000 (5000 rpm is the limit
on the Colortune) the necessary corrections can be made to get
it right. Not only can the full throttle conditions be
catered for in this manner, but so can part throttle and
transient conditions. For instance, a hesitant pickup when
going from part throttle to full throttle could indicate that
the mixture is too weak during the transition from one state
to the other. During the transition period and for a short
while after the Colortune should show a rich mixture
condition. If it doesn't, then you can bet your life that on
a fixed jet type carb, the accelerator jets or pump stroke are
inadequate.
Thank you

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Neil Bardsley
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Re: Anybody here use Colortune?

#17 Post by Neil Bardsley »

Steven Clarke wrote:I also doubt that you are really seeing the transition to the main jet when reving the engine to 2500 rpm there in your driveway. The rich mixture (yellow flame) that you are seeing is probably the result of the accelerator pumps adding fuel when you open the throttle.
A every good point. Thank you. Can you help my understanding of how accelerator pumps work? I thought it was a one off injection of fuel as I opened the throttle? If it is only the accelerator pump then if I slowly raise the throttle to about 2000rpm and wait the yellow flame should disappear and return to blue?

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Martin Benade
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Location: Cleveland, Ohio

Re: Anybody here use Colortune?

#18 Post by Martin Benade »

That is correct about the accel pump, but conditions inside the carb at 2000 rpm with no load are different from the same speed but with the throttle plates opened enough to be generating horsepower and doing work.
Cleveland Ohio
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