MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Lead Substitute and Colortune

Hey all,

I've unsuccessfully attempted to get satisfaction out of a Colortune on two different cars (73 & 74, both with HIF4s - AUD550s, I think). In both cases, as I set the mixture progressively leaner, I have orangy-yellow flames until the flame sputters and goes out (and then the car tries to stall). Running the car with this setting yields an over-lean condition -- at high speeds it really helps to pull the choke.

Do lead substitutes like CD-2 affect the color of the burn? I seem to remember something about the d-shell and chromatography from my chemistry and physics classes way back when, so it seems reasonable that a little sodium could make my burn appear a little yellow. I do not know, however, that CD-2 does in fact have this effect.

I could, of course, run the tank nearly dry and then refill without the additive and try to re-tune, but you guys seem to have a pretty good handle on most of these issues....

Thanks in advance.
Larry Bailey

Will add a bit to your question, Larry, and also ask if the fuels (concoctions) we burn today should have the same color characteristics as when these Colortune devices were introduced about 34 yrs ago? If nothing else, the "gasoline" we burn today smells nothing like it did years ago, and since aromatic hydrocarbons are a large proportion of what old or new gas is made of, I have often wondered if that alone isn't a giveaway that we are not dealing with the same stuff.

Any of you Petrochemical engineers out there, lets hear what you think! Thanks! :-)
Bob Muenchausen

Bob,

To add a bit of un-researched mythology: Is it true that in many regions in the US of A, some methanol is added to gasoline at the refinery? If so, I'd think that would change the color of the flame, since it burns much cooler.

I just don't know about the color-tune. It seems there are too many variables to think you could relate the color of your spark to how well your car runs. I hate to be negative, but I don't understand why a color-tune is better than tuning for best vacuum and smoothest idle. Maybe I could be educated?
Matt Kulka

Matt,

My understanding of the use of the colortune is that it's supposed to help you set the best possible burn: where your cylinders are getting just enough but not too much fuel. The idea is that a clean burn is indicated by a blue flame (like setting up the fuel/air mix on a bunsen burner). As you make the mix progressively leaner, you're supposed to see the yellow flame go away, indicating that you are completely burning the fuel in the cylinder. At that point your cylinder is getting all it can burn, no more and no less. To lean it out beyond that is starving your engine.

So much for the theory... my problem is that it doesn't seem to be working as advertised. So I'm wondering if it's me, or if it could be the CD-2 Lead Substitute, or if anyone else has seen this.

Take care.
Larry Bailey

Here is gunson’s web site
http://www.gunson.co.uk/
and here is the page which gives the contact htm.
http://www.gunson.co.uk/techenquiries.htm
BTW it would be nice if you could tell us what they say please.
Ian Holliday

I left a question on the web site regarding this thread, I'll post the company's reply.
I would expect that the burn color is not effected by additives or methanol, the color mearly indicates when the optimum burn is achieved (blue flame with a tinge of yellow). This should hold true for any fuel, at some point it reaches optimum burn. If you have orange-yellow, it is too lean. Of course, the company's reply may show I'm all wet! We'll see!
Robert Dougherty

Robert, I hope you are right as your comments are pretty much of what little I do recall from college chemistry 35 yrs ago. I just was not convinced that the flame color stayed the same regardless of fuel. As I remember it, we used to use the flame test in Chem 1B to see the different colors of the compounds or elements being burned. However, I am don't recall enough now to know if the Bunsen Blue test is valid in all cases for a combustion test. That's why I was hoping for one of our petro engineers to comment. I too will be very interested in Colotune's comments! Thanks for taking the initiative on this question! :-)
Bob Muenchausen

Robert,

Thanks. I also left a message with Gunson's yesterday. Seeing as how it's now 8pm on a Friday night there, I doubt we'll be hearing from them before Monday.

Since they've received two inquiries in two days, I'd be really surprised not to receive a reply soon.

Thanks again,
Larry
Larry Bailey

Larry,
I'm going to be away all week in Boise (Bob, I'll be on the lookout for your LBC!) so you'll hear before I do. I'll check the thread when I return.
Robert Dougherty

Larry:

You do realize that on the HIF4 screwing the air/fuel mixture clockwise richens the mixture and counter clockwise leans it? I’ve used the colortune before and found it to be very helpful in setting the mixture once you go the hang of using it. Carefully read the instructions that come with the unit and you shouldn’t have any problem. When I used it on my car I performed all the tests per the instructions. At the time I could not get the carbs set right until I used the Gunson. I have since gotten better at using the piston lift technique.

What you say?

Bryan
Bryan Prindle

Bryan,

Now we're getting to the heart of my question: do you use lead substitute fuel additives? I guess implicit in my original question is whether the problem is me, or is it some element in the system that I'm trying to test.

I mean, it very well could be that I'm doing something wrong, or not seeing something, or ...?

To answer your question, yes I am aware that CW sets the HIF4 richer. And, yes, I have followed the instructions explicitly (quite a few times, actually).

What I've finally found is that a barely steady orange works well on both of my cars (corresponding to the leanest smooth idle). I guess, then, that that's as good an indication as any (if you follow the letter of the law in the carburettor tuning section in the manual) as to when you're falling off the left edge of that plateau in their diagram (the one with the accompanying text that mentions "flats". Boy, did it take me a while to figure out what at "flat" is...).

Why should I care if the color isn't blue, just as long as I know what indicates the proper mix?

So, back to the original question: has anyone else experienced a blue-free colortune, and if so, could you determine cause?

Thanks one more time.
Larry Bailey

Larry. I have use the Color Tune in the past without any great success. Like you, I have never been able to obtain a "bunsen blue" colored flame. Here in my area of Arizona, we run "oxygenated" fuel all year round. Part of the year we have ether as an additive and part of the year we have ethnol (sp?). Neither of these mixtures seems to give the same color readings as the old, leaded gasoline. My Color Tune sits on the shelf gathering dust. A Gunson's CO meter, seems an excellent, if somewhat expensive, alternative. Especially for those of us who face emissions testing on a regular basis. There are much better test instruments today than Color Tune. As for the Gunson's website, I have tried several times to contact the company through it. They do not answer their e-mail. Les
Les Bengtson

Larry:

I guess what you're saying is that no matter how you set your mixture screws you can’t get that nice blue color. Here in TX I didn’t have that problem the last time I used the colortune. Once I got the hang of the unit it was very easy to see and adjust the carburetors. Blue-yellow-orange back to blue as you turned the screw.

One tip I will pass on to you as you try to tune your carbs is to only turn your screw a small amount at a time. At first I was turning a 1 / 4 of a turn at once. That’s too much. Each little movement goes a long way. Once I started just turning it an 1 / 8 or less I was much more successful.

Good luck this morning. I going to the Great American Race send off. You can view it at ‘www.greatrace.com’

Good luck!

Bryan


Bryan Prindle

Bryan: thanks for the pointers. I'm pretty sure I've been changing my settings in 1/4 turn increments. I'll try a more delicate touch (especially now that I've relocated that one little screwdriver that'll clear the brake lines and get into the rear carb...).

Les: I'm kind of a lurker here. I consider you one of the wizened gurus on this forum. It's good to hear that you've had similar experiences. Father's Day is tomorrow -- I wonder whether the wife could be persuaded to get me a Gunson's gas tester?

I'm on a heavy deadline at work (haven't had a single day off in a month and a half), but I'll try to get an hour or two in the garage and try Bryan's approach. I'll post my results.

Thanks all.
Larry Bailey

It sounds as if you have worn jets

this is very common with unleaded, particularly with swing needle carbs such as HIF44

with correct size jets (usually 090 on MGB) you should be able to get a blue flame on colortune, altho u will find some difference between the inner and outer cylinders on each carb

a problem which might affect some of you is elevation : if you are say 3000 above sea level then it will be very difficult to get it weak enough and different needles will be needed
chris

Chris. There is rather little difference between needles at the idle setting. Most of the variation is in the portion farther down on the needle. As to worn jets, perhaps, but I could not use the Color Tune to set up a brand new set of SU HS-4s several years back. Oxygenated fuel is becoming more common here in the US and our congress recently required a 500% increase in production of it. (The Ethanol variety--got to keep the farmers happy.) I have never met anyone, within the last ten years, who has been able to get a good tune using the Color Tune and their most common complaint has been the lack of a bunsen blue color. Old carbs, new carbs, it does not seem to make a difference. It is unfortunate that Gunson has not done some more recent testing. Since their product originally appeared, unleaded gasoline was introduced in the US and now oxygenated fuel use is being expanded. In the UK, unleaded, lead replacement petrol and leaded petrol are currently available (as I understand it). With all of these changes, I would think that Gunson's might do some updated testing and inform the general public--both those of us who currently own these tools and those who may wish to purchase them in the future. To me, the Color Tune is a unique tool which may have worked very well in the past, but does not form any part of my test equipment usage today. There are much better test instruments available. The cost of CO meters used to be such that only professional shops could afford them. Today, any serious hobbiest can. A much better alternative than a Color Tune. Les
Les Bengtson

Yeah Les,

I've had consistent results all year round with two sets of rebuilt carbs (including new jets), and one set of old ones on two different cars.

As I said before, it may still be a useful tool in that it allows me to see the point where the engine starts to miss (the orange flame begins to flicker). Could be that that point is where you used to get a blue flame... or not.

Anyway, I'm still stuck at work and haven't been able to get out and try Bryan's approach. Too bad: it's an amazingly nice weekend here in DC.

Larry Bailey

This thread was discussed between 12/06/2002 and 16/06/2002

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.