i was trying to tune my carburator (Skoda Felicia XL 2000) with the idle screw tuning to get the maximum stable vacuum, after i did this i realize that wen i disconecte a vacuum hose, letting air in the engine would accelerate, now this tell me that i have more gas than air so i adjuste the idle screw closing it and it seems that if you tighnen the screw, you let MORE Air in, if you uncrew or loosen the scre, is like MORE GAS is injected, can someone confirm or explain the reason for this,

Also, the reason i was doing this is to set the Warm up RPM to 1500, and to set the correct Idle RPM wich i thought it was 850, please confirm this.

thanks ind advance

are you sure you are using the right adjuster screw?? sounds like you are adjusting the idle mixture screw

are you sure you are using the right adjuster screw?? sounds like you are adjusting the idle mixture screw

the screw im refering to is the one closest to the carburator base / plenum

most engines idle at rich mixture conditions.

somehow if you let more air into engine fuel mixture becames leaner and engine revs up.

so its more easy way to control air with a screw instead of controling the amount of fuel.

most IAC valves operate in that way.

in my experience 1.3 felicia engines idle at 850 - 900 rpm with 10 - 12 degrees of ignition advance.

its very important that the idle is adjusted properly, this could mean the diference of a very economical car or one that guive poor performance, i went on a trip yesteday thats about 40km(24.6miles) and on a round trip this car used 2.5 galllons of gasoline. i say im averagin 33.6km/g road, and even less in the city, so you can understand why tuning my carb is important

i found out while reading in the internet that the idle screw of the carb is the one that controls the buterfly, the one that i'm refering to is the idle mixture screw as teflontom pointed out, i also found out that it can be lean in, or rich in, depending on the carburator tipe, so i took out the screw, and since is pointed, its a normal carburator so is lean in, but i'm lest wondering, if its lean in, why does it accelerate when more air comes in through a hose, and why doent it do the same when i turn in the screw some more

what sort of carb is it?? is it a pierberg? jikov?

stock carburator, i realy dont know what skoda uses, but i finaly understand how to tune the Idle and the idle mix after reading in the internet,

i adjusted the idle screw until engine reached 2000rpm, then adjusted the idle mix until max vacuum was reached (24) then i started reducing the idle speed until my vacuum niddle started to fluctuate a little (about 2 points up and down) checked rpms and then adjusted the idle mix for lean until vacuum started to drop, keeping the fluctuation the same, when the fluctuation increased i enriched the mix by ¼ of a turn and checked the rpm then adjusted the idle until 800rpm and vacuum fluctuation and vacuum reading stable.

i now have a perfectly tune carb for lean city driving, if you want to get rich (acceleration and power) all you have to do is turn the idle mix until vacuum reaches 24 and idle doent fluctuate the vacuum, and ofcourse, you'll have to turn the idle scre ½ a turn out to de-accelerate and set to 900rpm idle, that way you get a lot of kick good throtle responce and good power

i now have a perfectly tune carb for lean city driving, if you want to get rich (acceleration and power) all you have to do is turn the idle mix until vacuum reaches 24 and idle doent fluctuate the vacuum, and ofcourse, you'll have to turn the idle scre ½ a turn out to de-accelerate and set to 900rpm idle, that way you get a lot of kick good throtle responce and good power

See if you can set the mixture correctly using an exhaust gas analyser, disregard any CO level stated in a workshop manual and set it to lambda (λ) to equal 1 (providing it doesn't exceed emissions limits!) as this is the ideal running mix for all petrol engines, and once the idle speed is set correctly you'll probably find it will run better than before and be just as economical as your lean-burn mix. This method will also tell you if your carb needs replacing or servicing.

I did similar myself about 10 years ago to an old Peugeot 309. I fiddled and faffed with the carb. It was economical but the mix was so far out it would hardly tick over and although the CO was low, all the other emissions failed it at it's annual test! It was £15 well spent to get adjusted and set correctly, as it was more economical after it was done to the method I described!

Lambda refers to the 14.7 to 1 air to fuel mixture wich is the ideal.

Depends on the machine you use/borrow - some have a display just showing lambda with 1 equalling correct (below is weak, above is rich), others have a display with AFR.

I'm lucky in having a mechanic friend who lets me use his machine for a token fee.

i dont use those devices, all i use is a doctors stetoscope, a vacuum gauge and a electronical tester (i can even use it to check rpms) and my nose, yes my nose, i smell the exahust comming out of the pipe and know if its burning to much gas (cus when that happens the chemical that unburn gas produces is acid and smell like a tear gas bomb) if its burning too little gas the engine produces ozone(very noticeable cus its smells exactly like before it rains) its all about chemistry and knowing how certain chemical smells, anyway, i know this method works cus all the car i tune end up the same, with wather coming out of the exhaust pipe, jejeje