Looks like there'll be a dyno session in my near future. Thanks Guys!

The most important component of the dyno is the skilled operator...

A dyno measures torque ..full stop..

While running on the dyno the engine is usually connected to an exhaust analyser and an electronic engine analyser.

"Tinker" is a somewhat inappropriate word.   The operator "knows" what outcomes to expect from various adjustments.  More timing and more fuel generally means more power .. until you reach the optimum of each whereupon more will reduce power....

Its all about finding that optimum setting at various points throughout the rev/load range.  With modern data logging you can do this on the road...although WOT/max load (i.e. top speed) can be problematic unless you have access to a private road).  On the dyno you can easily stop the run, change carb or dizzy settings and go again.  With modern electronic fuel and timing controls this is also possible in real time.

Although, my favourite operator likes to point out that Mercedes race cars were producing huge outputs well before dynos were invented..... and the BMC Works guys never went near one .....

Cheers, Ian

Ideally the basic tune of the engine is already set before it goes on the rollers. A base line pull is then taken observing mixture and ignition for correct settings. Then adjustments to timing and mixture can be made to maximize what your looking for. max HP at wide open throttle or perhaps max economy. Each type of tune ie race or road use is different. That's the advantage of tuning on a dyno you can tune for purpose not just max HP.

I have no direct experience with dynos. So briefly, what kind of diagnostic information does the average dyno provide other than perhaps exhaust gas analysis and ignition stats? I know they can measure RPM, HP and torque. Do you just tinker with various adjustments; carb, ignition, valve lash, etc. until you see the HP and/or torque figures go up?

if your on a dyno then The color tune is superfluous you'd be using the dynos instrumentation. And in 40 odd years of using dynos I've only seen one accident, mind you I was in the drivers seat at the time!

Colortune is only useful on double carb'd engine  if you only have one carburetor it just doesn't make sense using it. just like  what a friend of mine told me, and i agree with him... if you tune one cylinder ,you are going to turn the mixture nut in the back of the carb either clockwise of counter clockwise to attain the proper tune,  then if you go to the next cylinder, again if it's not tuned, you are going to turn the same mixture nut in the back of the carb, THEN WHAT? by doing so it means it will going to upset the tunning of the first cylinder that you just did, and so on and so forth,, it's like a viscious cycle....i really regret buying my Colortune for 40bucks in eBay.  https://youtu.be/ASeMfXfjNpw 

and if you have more tunng question just contact Joe Curto, he's considered by many as the God of SU carbs, he can tune all types of carbs even when blindfolded.

A link to where one can find Vizard's article, try it if you dare:  Mixing it on your Own Dyno

Mixing it on your Own Dyno

by David Vizard

 

The average home tuner's most frequent problem, if the letter we get are anything to go by, is getting the fuel/air ratios (mixture) right after having tinkered wit hthe motor.  After printing this article, we do not expect to get, ever again, a Technical Query asking what needles or jets to use on a modified motor, becuase this really should be the end of your mixture problems!

 

When tuning the engine, it is more than likely that the fuel/air demand of the engine is changed.  Becuase of this it is neccessary to "calibrate" a carburetter so that it passes fuel into the engine in the correct quantities for the amount of air being consumed.  Over its operating range, a carburetter may have to pass a volume from say two to two hundred cubic feet of air a minute!  At tickover, the consumption of air is very low, but at full throttle the opposite applies.

 

At every point between the two extremes the air flow requirement is different, yet at all these points the carburetter is expected to mix the correct amount of fuel with

the incoming air.  There is little point in trying to set up the mixture at tickover becuase very few, if any, of us drive on tickover and there is absolutely no guarantee that the mixture is right throughout the range.

 

How do we know or how can we tell what the mixture is like anyway?  Up until now, the most common method has been to "read the plugs".  If you have had years of practice and are an expert plug reader (not the print on it) you can just about pull off the job of mixture setting.  The trouble, however, with a plug count is that one is never too sure what the plug is saying.

 

For instance, a dark, very slightly sooty plug can look like a mixture that is just a shade rich, but it could be that the mixture is just right and the plug type is too hard (runs too cold) for the motor.  Unless you are an expert then, reading the plug is, to say the least, just shade dodgy.

 

An alternative to reading a plug is to get your engine set up on a dynomometer; either the rolling road type or the engine type.  When an engine is on a dyno, it can be run at various rpm and against various loads, thus simulating the conditions met on the road.  While all this is going on, an electronic gas sampler can be analysing the exhaust and indicating the fuel/air ratio.

 

Going from reading plugs at a dollar a time to using three grand worth of dyno might seem like going from one extreme to the other or to use a comparison, going from an abacus to an electronic computer.  What is needed to use the analogy again is a slide fule ie: a method between the abacus and computer, or to come back to reality, a method of setting the mixture which is more akin to the dyno and mixture analyser than the plug reading method.

 

A dynomometer measures horse power, commonly called brake horse power becuase a dyno is nothing more than a brake, calibrated to read out the work absorbed and the rate of absorbtion.  Here we have a clue; all cars have brakes (or

should have) so what we have, in effect, is an uncalibrated dyno fitted to our car.  To simulate road conditions whilst standing still, all we need do is to jack up the driving

sheels of the car, put it in gear and use the throttle as if we were driving along the road.

 

To simulate road levels we need only apply varying pressure on the brake pedal.  Such action will, of course, get the brakes hot.  For our purposes we need to be able to hold full power for about fifteen seconds maximum.  If your brakes cannot cope

with this from the heat point of view, then you are sadly lacking in that department so see to it.  It's probably better brakes you need and not more power!

 

Okay, so we have our dyno.  The fact that it does not read out in horsepower is, for our purposes, irrelevant.  What we need now is a mixture analyser.  Up until a few years back this would have cost a tidy sum.  These days we have a device known

as a "Colortune" and within the price range that can be afforded by the enthusiast, this is the _only_ device we know of that will do the job in hand.

 

For those who man not know, a Colortune is a device which replaces the sparkplug in the cylinder.  The top of the Colortune is made of a Borosilicate glass and this allows you to see what is going on in the mixture combustion chamber.

 

Different mixture strengths burn at different colours.

 

By looking into the combustion chamber through the Colortune we can get a good indication of the mixture strength prevailing.  Inspection of the flame color shows that four fairly distinct stages occur.  when the flame colour is blue/white, the mixture ration is between 16 and 14:1; a blue colour indicates a mixture strength between 14 and 12,5:1; a blue/orange colour indicates 12,5 to 11:1 and orange indicates 11:1 or less.

 

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, the 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 at the Colortune and at this point it will reveal what the fuel/air ratio is under the prevailing conditions.

 

It can then be noted, preferably 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 parth 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.

 

On carbs like the SU and Stromberg CD variety, a lean mixture during the acceleration phase would indicate that the damping is insufficient.  A thicker oil is usually required to compensate this.

 

A couple of cars were used as guinea pigs to test the method. Both cars were modified and therefore required different carb settings.  In each case the carburation has been originally set up by the owners who had only an average working knowledge of what was required.  After use of the Colortune by the method just described, both power and economy were better between 5-8bhp and 10-15 miles per gallon.

 

The reason that consumption was so much better after use of the Colortune stemmed from the fact that the mixture was originally set rich for maximum power and unfortunately becuase of the guesswork method of setting, it was too rich.

 

The performance increase was better than the power increase alone suggesting that the mixture was right (within limits) throughout the rev range.  As a side effect this led to a smoother running engine with a snappier throttle response.

 

To sum up, the Colortune proves to be a very useful device. It can, at a price of 4-87,5 UKP easily justify its place in the tool kit of any self-respecting enthusiast, and its intelligent use can only bring about an increase in performance.

 

Editor's note:

 

Whilst David Vizard has used this tuning method successfully with both a Mini and Austin 1100 its use on many other types of car could possibly be dangerous.  Firstly therefore we recommend that the suspension characteristics and drive shaft-prop shaft geometry of the car in question be checked carefully before even considering use of this method.

 

On rear wheel drive IRS cars which may have large wheel angularity, attempt to jack the car at points on the suspension that will allow the wheels to assume a position in

angle similar to that which exists in normal use.

 

On a non-IRS rear wheel drive car jack under the springs on

either side at the axle location point.

 

Make sure jacks are very secure and will not move under testing vibration, also make sure any car to be tested has alternate props underneath in case of jack failure -- ie: spare wheels and tyres which should be first tested using the full weight of the car.  One advantage of the DV method is of course that during load tesing the wheels on the ground have the brakes applied.

 

On a Mini the best method Vizard found was to put a piece of wood on top of trolly jack lift point and jack up from the Mini sump.  Once having jacked car up, jam wheels and tyres underneath car for safety.  Car does rock but cannot thus fall over.  Drive shafts will assume peculiar angles during testing and this can be minimised by supporting bottom suspension arms on axle stands --these can however move and you may have to take the risk of the odd shaft angles for the few moments of testing.

 

This method does not apear to be practical with swing axle IRS cars ie: Herald, Spitfire, Vitesse Mk 1, GT6 Mk1.

 

*article originates from Car and Car Conversions from many years past

Well I guess you're right. The colour tune will tell you which of your two identical carbs is running slightly richer than the other, and allow you to balance the two theoretically identical carbs.

At all non load sites.

Unless you have a dyno, where you can look at areas other than the last 3/8" of the thickest end of the needles.

Even then though, I suspect that you will soon find the colour tune won't allow a consistent spark as soon as cylinder pressures increase. 

At which point, the use is gone. 

So it it has its place. Yes. On 100% stock engines with factory carb setup. Where you know if you're good at idle, you're good everywhere.

Add in any of these: free flow exhaust, free flow air filter, ported head, cam, rockers - now the colour tune is a balancer only, or good for setting up zero load site points, unless you have a dyno, and then only until the spark is blown out over that huge gap under the glass window. I guess you could put a CT in each plug hole so they'd all be equally bad however.


Really, If you had access to a wide and, the colour tune is only to those with twins, or as a diagnostic tool perhaps for stablishing issues with single cylinders, but even then, what would it assuredly tell you that spraying WD around the intake flange, pulling a plug lead off, switching leads, compression test, and leakdown wouldn't? 
I might have one somewhere still, or I might have thrown it away. Suffice to say, since I got a wide band many years ago, I've never once needed to come close to questioning where my colour tune is.

All said,  I would be curious if the colour tune changes colour as the dizzy is swung; I suspect it would be very little, barely identifiable, compared to a flaky mixture. 

Because it samples the exhaust flow from all four cylinders at the same time, it seems to me that a wideband O2 gauge is more of a monitoring tool and not so much of a diagnostic tool. It will alert you when an air/fuel imbalance exists, but cannot tell which cylinder or carburetor is at fault. It also seems that you could have a condition where one carburetor is running too lean and the other carburetor is running too rich but the O2 gauge would average the two and indicate all is well.

The ColorTune on the other hand will indicate which cylinder is at fault and therefore which carburetor needs to be adjusted, provided the tool is sensitive enough to be meaningful.

I have no direct experience with either method, I'm just trying to get my head around the theory of each tool and their strengths and weaknesses. I have a bung welded into my downtube and will most likely install a wideband O2 meter at some point. But I'll be relying on the ColorTune to dial in the correct air/fuel ratio's.

Quote: Originally Posted by 1963SV2
…howerver, the problem is that the colortune/SU only really works at idle.

After reading the instructions it sounds like the ColorTune is almost useless at idle – it will always indicate an overly rich mixture. It's at mid range and redline when the colors go from Bunsen burner blue to whitish blue that indicate a proper air/fuel mixture. 

Quote: Originally Posted by 1963SV2
…the SU works on a combination of throttle opening and load. It can be done using the [ColorTune], Vizard describes a technique, but its not something I would try.

Yeah, I read about the SU throttle vs. load thing and how unusual that is compared to a conventional carb. Pretty cool! Where does Vizard talk about the ColorTune, "Tuning The A Series Engine?"  The lack of an index makes that book a nightmare to find anything. 

Color tune was around before colour television. They really are that ancient.

Even Wideband O2 sensors are a decade old, but are affordable at least:
//r.ebay.com/ew475s

These will tell you the mixture at all speed and load sites. No more removing spark plugs and D***ing about trying to figure out what's going on anywhere other than idle.... 

Buy one if you really want to figure stuff out. If you just want to watch the pretty colours as you rev your engine, crack on with the black and white...

Use a wide band O2 sensor, also called an AFR sensor or Air Fuel Ratio Sensor, mounts in same bung as O2 sensor, buy the way you will need to drill a hole and weld the bung in place, ideally close to where all three exhaust pipes come together flow wise. Color tune is still a great way to balance across cylinders, or you need to weld in 3 bungs.

The CT is quite sensitive (if a bit hard to read)....Howerver, the problem is that the colortune/SU only really works at idle.  The SU works on a combination of throttle opening and load.  It can be done using the ct, Vizard describes a technique, but its not something I would try.

Today one would use a O2 sensor and data logging instead.  ..... or a dyno.

Cheers, Ian

I'm looking for someone who considers themselves an expert with the Gunson ColorTune. Here's my question: has anyone ever compared the ColorTune with real-time dyno results?

My twin SUs are in tune and my timing is correct; my Mini is running great—and of course, ColorTune is showing all the right colors. I'm trying to establish a baseline and just wondering how far out of tune my motor has to be before ColorTune starts indicating that there's a problem. Is ColorTune highly sensitive to carburetor maladjustments and ignition timing, or is it a dull tool sensitive only to major carb and timing issues? Any thoughts?