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MG MGB Technical - current use of a gunson colortune


'79 mgb

several authors in recent, last few months, postings have suggested that because of changes, additives, in today's gasoline that the colortune was no longer all that good to use. but, it is what i , and others, have to do the job.

ok, then to compensate, should one advance or retard the setting and not use the abrupt change from yellow to blue as being the correct mixture setting, that is,for example, go past the sharp change to lean it out a bit. or the opposit ?

or, assuming the major culprit in today's gas is the 5% added ethanol, should one advance or retard a bit ?

yes, i know that one is advised to go only in the direction of from rich to lean and not go back and forth, but like adjusting the timing, a little trial and error should do the job.

thanks for all comments

john sutter

John - I have been using a color tune for the past 20 or 25 years and have no problem with today's fuels. The biggest thing with the color tune is that is should be used in low ambient light. Using it outdoors in bright sunlight will wash out almost all color when trying to view it. I have always used it in my garage whee the light is not as bright. When I first saw the color tune demonstrated (nearly 30 years ago), the gentleman demonstrating it admonished us that it needed to be used in dim ambient light or we would not see a good color change.

I also adjust the carbs for the correct color, then turn the adjusting nut one flat back for a slight bit richer mixture to avoid any burned valves. Cheers - Dave
David DuBois

I only tried one about 40 years ago, and couldn't get on with it compared with using the lifting pin and Mk1 ear, which I've been using ever since.
Paul Hunt 2010

I found the only disadvantage with a colourtune is having to stop half through to switch carbs. I remedied this by buying a second coloutune. What ever method you use, a clip on tacho is a real help, and a Krypton Synchro Check for balancing is worth looking for.
c cummins

I have always had a colortune plug since the sixties.
For the past 26 years it has been a valuable tool,in addition to the gunson exhaust gas analyser,to use when tuning my '77 MGB for smog check. If the engine is running on the rich or lean side after warm up,I start to adjust the carb. in the direction to achieve the bunsen blue flame color regardless of fuel and do not have any problems passing the test.

Paul like you, I still use the lifting pin and my ear to
tune twin SU carbs.

Hartley Mayers

Clip-on tach? I know a clip-on timing light is much more convenient than the old-style series-connected 2-wire type, but I don't see where a clip-on tach comes in, unless you just mean a croc-clip on the coil -ve.
Paul Hunt 2010

thanks !!!

with the original equiptment on my 79 mgb, i only have one carb !, in this case an advantage.

thanks for all the comments, you answered all my concerns .


john sutter

This thread was discussed between 17/04/2010 and 20/04/2010

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