Fuel tweaking

[siteunseen]

So if I understand this Tech Tip courtesy of Blue, counter clockwise leans it? Clockwise richens? Mine is running really good and temp is cooler, gets great gas mileage but my plugs might be a little dark. So I think I should turn it counter clockwise just a scratch, correct?

http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Edited July 20, 2013 by siteunseen

[Wade Nelson]

We really don't need to discuss moving your arse cheeks up and down in a forum about classic Z cars, do we?

What? Tweaking?

Not TWERKING???

*Nevermind!*

[madkaw]

Isn't it righty tighty(lean)- lefty loosy( rich)

I guess it could be a matter of perspective , but think of it as a bolt that your installing. No matter what angle your at, it's still the same. I would say you need to turn clockwise to lean out your dark plugs.

Remember that the mixture knob does not make changes across the entire spectrum of engine performance. Give it a shot to see if it cleans things up.

Other possibilities are float adjustment, piston needle size or position.

Hope I answered your question

[siteunseen]

Other possibilities are float adjustment, piston needle size or position.

Hope I answered your question

I apologize madkaw, it's my FI '77. By what I read in the Tech Tip is to turn the pot clockwise for more fuel, think of a volume knob on your stereo, so lefty loosey would turn my fuel supply/volume down? I'm about to go for a rip and see.

Wade it's Twurk not Twerk, google "Ying Yang Twins Thug Walkin'". Songs 3, 11 & 12.

Edited July 20, 2013 by siteunseen

[Zed Head]

I might be wrong here, with the electrical terminology, but I think that it depends on which side of the potentiometer you are using as a rheostat. If you wire up one side, it will be clockwise, the other it will be counterclockwise. Only two of the three pins are used. So yours could be either way, if you didn't measure resistance before you installed, you'll just have to turn it and use your nose, or the seat of your pants.

Actually, I see that it's referred to in the atlanticz.ca page that you linked, about 1/3 down. I don't think it's necessary to short two pins together as shown, but apparently it won't hurt anything.

[madkaw]

Oops!!

[siteunseen]

I did solider those together so do think I'm right in more volume = more fuel? I know all I have to do is read the plugs after a few drives but I'm lazy and would rather type in the A/C than pull the plugs in my hot arse garage.

[Captain_Zeros]

if you've got a multimeter you can probe the resistance of the potentiometer and see which direction is more resistance and which direction is less resistance. (I forget which gives you more fuel though, I'm a carburetor guy! I'm sure somebody will chip in)

[Zed Head]

More resistance will give more fuel. Most of the potentiometers available will give way more resistance than needed, enough to flood the engine out. The engine probably wouldn't even run if you had the knob turned to full rich. So whichever end of the rotation it's at now is going to be the lean end.

[FastWoman]

A lot of advice, mostly correct.

The shorting of those two pins -- the wiper contact (middle) with one of the strip contacts (end) -- is a method used by better electronics designers to ensure that the resistance never gets greater than that of the strip. If for any reason the contact between the wiper and the strip gets dirty or corroded, this would prevent the resistance from jumping periodically to infinity. It's a small refinement and is not absolutely necessary (or in any way particularly consequential).

MOST potentiometers are built like this:

FED: Intro to Physical Computing

So you can imagine the internals, even though you can't see them. The resistance from A to B is always the stated resistance of the potentiometer (e.g. 5 kOhm). If you turn the wiper all the way to the "B" end of the resistance strip, as shown in the diagram, the resistance will be (almost) zero from W to B, will be the stated resistance of the potentiometer (e.g. 5kOhm) from A to W. If you turn the wiper halfway, the resistance between A and W will be equal to that from W to B, which will be half the stated resistance of the potentiometer (e.g. 2.5 kOhm).

If you short A and W together, then the resistance from A to B will be the stated value of the potentiometer (e.g. 5kOhm) when the wiper is turned all the way to the A end of the strip, and it will be zero when turned to the B end. Wired this way, and again referring to the diagram, CCW (towards A) would be richer, and CW (towards would be leaner.

[FastWoman]

And another note: Blue recommends the 1-turn control-type potentiometers such as you would turn with a knob. However, this is actually a poor choice. It is too easy to knock one of these out of align. My most favored choice would be a 20-turn trim-type potentiometer like this one:

043P103 - VISHAY SPECTROL - TRIMMER, POTENTIOMETER, 10KOHM | Newark

Adjusting from one end to the other requires turning the little worm screw with a screwdriver. It's very precise and very hard to knock out of align. The potentiometer is also extremely well sealed and will not easily corrode or get dirty inside. But if you don't want to go that route, then you should at least use SOME form of trim potentiometer:

https://www.google.com/search?q=trim+potentiometer&rls=com.microsoft:en-US:IE-Address&tbm=isch&tbo=u&source=univ&sa=X&ei=mEbtUcnhEuSqyAHEvYHYCQ&ved=0CGMQsAQ&biw=1237&bih=837

If it's not completely sealed, like the linear 20-turn ones, then my advice would be to use one that's open enough that you can smear the resistance strip with dielectric grease -- for instance this style, which you adjust with a screwdriver in the center hole:

http://www.ictradenet.com/models_pic/EVN-64AA00B32.JPG

Edited July 22, 2013 by FastWoman

[siteunseen]

Thanks Fastwoman for the info and part #s. I was initially trying this out to see if it's what was wrong with my stumble at lower RPMs so I ran it into the cabin to play with while driving, $5 from a local Radio Shack. Well it was exactly my problem! Now I will buy one like you say and permanently mount it inline with the coolant temp sensor wires above the intake. I've got that 240 paid off and can now finish my 280 with new interior and a sound system so the potentiometer knob I have in my console volume hole has got to go.

Well after re-reading everything I'm still wired up like Blue's so CW=more fuel, CCW=less fuel. From Tech Tip " Note: the center and shorted pins on the pot are connected to the sensor and the other pin is connected to the ECU if you want to add more fuel by turning the pot clockwise."

Edited July 22, 2013 by siteunseen