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Technique for matching idle mixture?  Rate Topic 
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 Posted: 07-31-2010 09:12 pm
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subwoofer
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I just got myself an IR thermometer (up to 1000ºF), so I was thinking that could be the best way to match idle mixtures for all the throttle barrels.

In theory, when all cylinders run at the same temperature and the same vacuum, they should also have the same mixture. Any objections to this?

I can see the procedure developing like this:
- Run the engine nice and warm, drive a lap around town.
- Double check balance of carbs with 4-channel CarbTune
- Let it idle with the bonnet open for a few minutes, measure temp of header pipes about 2" from head.
- adjust idle mix until all cylinders are as close as possible.

The time constant of the temperature change is a large unknown here, I really don't know how long it will take from making a change till it will register consistently.

Do people have any thoughts on this? I am thinking this as a poor man's 4-channel EGT system.

--
Joachim
The measurements take seconds

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 Posted: 08-01-2010 04:17 am
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Jensen Healey
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I don't understand the need. A 4 tube manometer will get the vacuum balanced. If you discover the temperature is off and adjust accordingly, the vacuum will then be off. No?

Kurt

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 Posted: 08-01-2010 07:28 am
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subwoofer
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EGT is an indication of the air to fuel ratio among other things. The vacuum is an indication of the amount of air going into the cylinder, you would have essentially the same vacuum even if the cylinder wasn't running at all (i.e. no fuel or spark). Valve overlap causes this to not be absolute, but for this purpose I think it should be close.

Since there are two adjustments for each cylinder, we need to measure two things to know both are right.

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Joachim

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