Hi all I have my engine running well enough having followed the Birdman tutorial (thank you Birdman) for setting up the carbs on my 79 308 GTB, but at idle it is rich and I am struggling with the idle mixture screws and going by ear as to how the engine is running. As such, I am planning on using an exhaust gas analyser. The manifolds on the car have the little testing ports for each cylinder as original - but these are too narrow (a thread of about 5mm in diameter) for the gas probe on the analyser to fit in. I don’t suppose anyone has any suggestions for how to make this work, before I attempt contraptions which will probably lead to melted pipes and carbon monoxide poisoning…. I could, of course, get an overall idea by putting the probe in the exhaust, but it would be great to be able to tune it by cylinder. Many thanks.
Those riser tubes were not intended for a modern probe. I would offer that using glass Colortune Plugs was the period correct way of dialing in the A/F ratio. Others may know more, but that's what my first mechanic used..
Good day BT, Indeed the ColorTune is very helpful and could be all that is needed. However, the accuracy is not absolute and is based upon an observer's interpretation of the color. Secondly, Colortune cannot tell you the full story that a 4 or 5 gas analyzer can. For example AFR is ratio of air and fuel and so if something is amiss how do you know which of the two are causing the less desirable AFR? Is it too much/too little fuel or air? What about CO or NO levels which can help identify other issues. Should everyone have a 4/5 gas analyzer? Nope, but one should understand the limitations of using Colortune or a Wide Band O2 Sensor as part of the tuning/adjustment process. Cheers, Sam
Thanks for the replies all. I’ve seen the other posts on colortune, but to my amateur eye it looked tricky to use/see, and I was thinking the ‘digital’ nature of the gas analyser may take some of the judgement out of it. On the risers, it does make sense that they didn’t have a modern probe in mind. I will try making an adapter, but I am worried it will restrict the gas flow even more to the probe which might not be enough for a reading, but I will try it.
Good day Pedders, The Colortune will be far easier to use, as you simply replace your current spark plug with the transparent Colortunes spark plug and then observe the resulting color that you see from this transparent plug. You then compare the color seen to the colored chart included with Colortune and determine the approximately AFR from this chart. It is very easy to use and will allow you to dynamically see any mixture changes you make to your carbs and will get you into the ballpark in terms of the car's AFR value. I would try Colortune first and if you are still having issues and/or need more data regarding your engine's combustion, then certainly the gas analyzer will provide you with that information. That said, you will still need to interpret the gas analyzer's values and know how to adjust your carbs to meet your gas data target values. Cheers, Sam
Just a quick update to say that the Colortune worked a treat. It took me a while to get hold of one, but eventually Amazon came through. Being able to see the effect of tweaking the mixture screws on the combustion in real time was really helpful - caught a couple of cylinders that were way off (rich) too. It wasn’t tricky to use, albeit the front bank was a little more challenging. Car now idles very nicely and doesn’t smell like fuel must be leaking out of the tanks… Thanks for the advice, all. Image Unavailable, Please Login
