Hyundai Forums banner

1 - 6 of 6 Posts

·
Registered
Joined
·
793 Posts
Discussion Starter · #1 ·


A friend pointed out an a/f setscrew and idle setscrew on the passenger side of the engine. I'm not sure which is which.

I've already changed the oil, air filter, breather filter, spark plugs, wires, distributor cap & rotor, and fuel filter.

Fuel economy was 20mpg (usg) & now it's just baaaarely any better, if at all. Fueleconomy.gov says others are reporting 24mpg in real world driving & I'd love to get that. (No, I don't drive it hard at all.) I've noticed that the exhaust smells quite strongly of gas, especially at startup. I'm pretty sure every cylinder is firing now, so the only thing I can think is that it must be running too rich and needs to be adjusted.

In addition to which setscrew to adjust, how do I go about telling when it's right w/o some sort of gas analyzer? Just a sniff test of the exhaust?

Any help/info is appreciated. Oh, and yes, I did check the owners manual maintenance section and there isn't anything in there at all about this.
 

·
Registered
Joined
·
1,262 Posts
Older vehicle...

By the looks of it, we are looking at a 20+ year old vehicle. You may or may not have access to the idle mixture screw which will really not affect your over all fuel mixture and economy. The idle circuit is out of the picture very shortly after accelerating from a stop so don't expect fuel economy to change by adjusting the idle mixture.
Also, the screw may be blocked with a plug. It can be removed so you can adjust the mixture. Find yourself a repair manual at the library or from the dealer if available.
Good luck on your journey.
 

·
Registered
Joined
·
793 Posts
Discussion Starter · #3 ·
Yes, it's a 20+ year old 1987 hyundai stellar 2.0.

A friend pointed out two set screws on the driver's side of the engine and said one was the idle set screw and the other was to adjust a/f mixture. I can't recall which he said was which.

Makes sense that adjusting the idle won't affect driving fuel economy, but if the other setscrew is to adjust the a/f mixture then it makes sense to me that adjusting that could lean out the fuel mixture and improve efficiency.
 

·
Registered
Joined
·
793 Posts
Discussion Starter · #4 ·
As for getting a repair manual.. I googled and found one on amazon for $76. Kinda pricey just to find out if I can adjust the a/f mixture somehow, and how to detect when it's set properly. Hence asking here on this forum..
 

·
Registered
Joined
·
1,005 Posts
A friend pointed out two set screws on the driver's side of the engine and said one was the idle set screw and the other was to adjust a/f mixture.
That is a quite common layout of carbs just before fuel injection became mainstream. It is called mixture recirculation.
There is one setscrew for a/f and one for idle speed - which used to get adjusted by the throttle stop screw before.
I could elaborate more why and how etc... but to make it short:
Both of them only influence IDLE (speed and mixture) - you seemed to miss that point of himilcyclr. The mixture at driving load (i.e. anything above idle) is influenced/set by fixed jets and can only be altered by replacing them with others.

So which is which ? I don't know this actual carb but I suppose the two setscrews are of different size. If so the bigger one regulates idle speed by amount of bypass air to the throttle plate and the smaller one regulates mixture.

B.t.w. also such carbs have a throttle stop screw but usually it's well hidden/covered since messing with it will do big damage to the overall adjustment.

And: How to detect it's right ? No chance without an exhaust gas analyzer, minimum requirement is one that can tell about the % carbon monoxide in the gas. Better ones can quantify HC, CO, CO2, O2.

So in general these setscrews are not the general 'lever' to tune fuel economy but if these two are totally out of adjustment they may negatively influence FE so it's worth to have that checked - by a shop with the necessary knowledge and test equipment.
There's good reason why there is no mention about it in the user manual.
 
1 - 6 of 6 Posts
Top