Beyond a standard tune up

[Jeff C.]

It seems to me I'v heard of using exhaust gas port temps as a fuel/air mixture adjustment tool. I think they were using a non contact laser gauge as a tool. I'm trying to fine tune a 62 340HP with the correct 3269S Carb that has been rebuilt. Has anyone heard of this?

[Clem Z.]

Re: Beyond a standard tune up

stock carbs are jetted for sea level and you should reduce the AREA of the jetting 2% for every 1500 feet you are above sea level. any other means of tuning the carb will need a chassis dyno to get reading under load.

[Terry M.]

Re: Beyond a standard tune up

I have seen photos of engines on test stands with thermocouple leads coming from the exhaust manifold/header ports. I would think these temperature readings were being used as a tuning aid.

Now to do the same thing with a engine in a car that is in motion would require a whole other test apparatus to get those readings, but it certainly could be done.

I once went to Bonneville -- something every gearhead should do at least once in their life -- and saw a GM G-van which was receiving data from a race vehicle -- a truck I think. They had enough antennae on that thing to have gotten all that kind of data. It looked like something from a si-fi movie. No I couldn't get inside. I suppose one might consider the budget one would need for such a task.

All that said, a simple IR temperature gun, relatively inexpensive now days, might work for idle and no-load tuning – but that is just a small part of the bigger picture.

[Joe C.]

Re: Beyond a standard tune up

The measurements will vary considerably, based on the location of the thermocouple used. Refer to the attached discussion.
There is a very simple "rule of thumb" method, using an IR thermometer, which should put you in the ballpark. I have not actually used the IR thermometer method, as I suspect that it will not be useful as an A/F ratio adjusting tool. Some have claimed that the measured temps actually drop, noticeably, based on idle advance adjustment.
If you need to adjust your A/F ratio, I would suggest that you purchase/borrow/rent or pay someone who has a proper A/F ratio probe.

Joe




http://www3.fs.cvut.cz/web/fileadmin/documents/122

[Verle R.]

Re: Beyond a standard tune up

If you installed a thermocouple in the exhaust port with a temperature gauge in the cockpit and a knob to adjust the area (move a metering rod) of the cruise jets you could optimize the mixture, and you would be duplicating the "cruise tuning" used in some older light airplanes. I don't know if they still do that with modern airplanes.

Of course, you would need to know the optimum temperature for your engine.

Verle