mixture setting tips!!

run up to warm, let it idle
depress brake pedal, if the revs drop, it is too rich, lean it out till you can press the brakes without affecting the revs, then reset idle at the throttle body!!!!

easy!

Cool - will give this one a go  8)

Rich

tis blindingly obviouse really as the brake servo takes air from the inlet manifold, i met a random bloke well into his 60s who was ex british leyland, i tried it and it worked!!

Nice tip! I know a little method you can use for determining if your car's running lean or rich, at any revs, but its not as good as that one. You wire up a switch and +12V to the 5th injector and if the revs increase when you add a little squirt o fuel, you were lean; if the revs drop, you're rich. Since the K-Jet tends to run lean in midrange, part throttle openings, correct running means the extra fuel will initially add revs, then after around 2-3 secs, they'll decrease. After a while you can gain a feel of how far out the car is.

Gunna try this method

I'm amazed this is how you'd try to set up the mixture on a car

it passed its mot a few weeks back on this set up, and on the r/r with gas analyser was 1/8 of a turn lean!

But apart from the fact you have absolutely no idea what afr you are running someone else could try this and have a small vac leak and completely screw up their mixture

Messing about with this is potentially going to screw up your engine in a big way. If nothing else at least pop out your plugs frmo time to time and check to see what's going on but this really isn't a very scientific approach

Not having a go or anything, just amazed you'd do it this way

of course it depends on your engine not havin false air, i sort of assumed that, as any amount can cause no end of problems.

not to sure how it could screw up your engine in a big way tho,

the principle is basic, as you are essentially setting it from what your engine is telling you.

You aren't actually looking at fuelling in any way nor the emissions. Therefore if you alter your mixture to run lean you can cause detonation i.e. serious problem

It's just something that I'd expect to do in a deterministic and controlled manner

JSeaman said

You aren't actually looking at fuelling in any way nor the emissions. Therefore if you alter your mixture to run lean you can cause detonation i.e. serious problem

It's just something that I'd expect to do in a deterministic and controlled manner

You're measuring an indirect thing which is a consequence of the mixture. As can be seen, in cabriaulait's case, it worked - because it was later checked using proper tools! Leaning out the mixture small amounts, is not unsafe - you'd have to approach the lean misfire limit to do real damage.

"You're measuring an indirect thing"
Exactly the problem

"which is a consequence of the mixture"
And other things

"you'd have to approach the lean misfire limit to do real damage"
Yes and you're testing at idle - it is completely different under load

no its not,

the afr is controlled through out the rev range, by the shape of the cone the airplate rises through.

it is a basic principle, that if your engine demands air from the brake servo, then it is runnin too rich,

the opposite applies, if there is no difference in revs when you depress brake pedal, then it MAY be runnin too lean, in this case richen it up till you hear a rev change then lean it back down till u dont, thereby finding the original setting that the engine was designed to run at (or dependant on wear, how it wants to run now)
spark plug check b4 and after is very usefull, to give the initial indidcation of how your engine is runnin.

You mean you think setting the AFR at idle sets it up for the whole rev range?!  :?

"it is a basic principle, that if your engine demands air from the brake servo, then it is runnin too rich"
It's a bsic principle that you measure the amount of O2 content in the exhaust to see what's going on.

At least we agree on the spark plug check

''You mean you think setting the AFR at idle sets it up for the whole rev range?!  ''

yes

search this

rollin road RESULT!!!!!!!!

have a look at page 2

also check paul c's thread on air fuel ratio testing, in mods i think

the mixture adjustment screw DOES set the fuel mix FOR the rev range.

answer me this, how else would u set it?

I'm guessing you are dealing with a standard car where you don't have to get too involved with AFRs?

You can have a safe AFR at idle/low revs and be dangerously lean higher up the rev range.

how else do you set it? Using a dyno, monitoring O2 against rpm etc etc etc and then make it safe in the whole range.

Your idea of introducing air to the system to test for rich and lean is ok in principle but you're doing it in an uncontrolled way because you're not monitoring anything

If you disconnect the servo vac line and open it fully then close it fully you'll be able to see this effect far more but again, it's not something I'd want to do without knowing what's going on in the engine

The plugs don't lie so they can tell you what's going on. You can also look inside the cylinder during combustion to see the colour of the flame but I'd be looking at exhaust gases for any kind of tuning

''Your idea of introducing air to the system to test for rich and lean is ok in principle but you're doing it in an uncontrolled way because you're not monitoring anything ''

i didnt say i introduced air, i said IF  the revs change when u depress the brake pedal then its too rich, simple!

''how else do you set it? Using a dyno, monitoring O2 against rpm etc etc etc and then make it safe in the whole range.''

so the only way to set the mixture is on a rollin road, with a gas analyser throughtout the rev range.
if you were to set the o2 levels at 5000 rpm i gaurantee your car wouldnt idle!

somehow i cant see vw designing an engine that was that complicated tbh.

the kjet is a mechanical system where the fuel ratios are set throughout the rev range,by a plate and a cone.
 if its right at idle, its right, sorry!

Err, OK but presumably the reason you're saying pressing the brake pedal alters the mixture is because of the vacuum connection to the brake servo i.e. you're altering the amount of air into the engine? Or was there some other reason that I missed?

"so the only way to set the mixture is on a rollin road, with a gas analyser throughtout the rev range"
Properly, yes.

"if you were to set the o2 levels at 5000 rpm i gaurantee your car wouldnt idle!"
No you need to set the values to a range that's safe throughout the whole rev range not at max power etc

"somehow i cant see vw designing an engine that was that complicated tbh."
Maybe it's not a complicated engine and if it's stock and everything works properly you can set a safe ratio by twiddling adjustment screws but my point is that you can't tune an engine in a safe manner by pressing a brake pedal.

''Err, OK but presumably the reason you're saying pressing the brake pedal alters the mixture is because of the vacuum connection to the brake servo i.e. you're altering the amount of air into the engine? Or was there some other reason that I missed?''

ok, x spark + x fuel = x air
spark is set, fuel is set (at idle mix screw) air is on demand!
if your engine demands more air than is available due to the afr, it will take it from any available source, ie false air or brake servo.
by pushing the brakes, u are only doing what the car is expected to do under normal circumstances, i cant see vw designing an engine that reduces braking effort at idle, implying that the correct amount of air to the amount of fuel required will NOT affect something as important as the brakes.
i truly honestly see where your comin from, but alot of fuzzy logic goes into these engines, sometimes it can be hard to see that something so simple could be so effective.

as far as my engine goes we shall be at vwaction in a few weeks.
as pointed out b4 my r/r thread describes my mods.

Exactly so you are using the dormant air from the servo. This is a small amount of air and certainly not enough to properly set up the afrs.

I agree that pushing your brakes is a perfectly acceptable thing to do at idle and braking effort should be adequate at idle.

"alot of fuzzy logic goes into these engines"
You'd bloody hope not!

"it can be hard to see that something so simple could be so effective."
I'm all for simplifying things, believe me I really am. I am just trying to voice concerns about setting up probably the most cruicial parameter you can alter without any test equipment.

Perhaps this is some magical trait of the Golf that just so happens to perfectly set up a safe AFR throughout the entire rev range … but then again maybe not! I'd honestly love to know if it was but the only way to tell for sure is with a whole bunch of cars and a whole bunch of monitoring equipment which I doubt we'll ever see