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mustbfaster2

Hey guys....its spring time again and I'm hoping to actually drive my car this year. Everythings fixed for the most part except one thing. The previous owner tried to adjust all the air/fuel settings and they are all way off. The idle screw, butterfly valve stop screw, and fuel mixture screws all need tuning. I've got them set good enough for the car to run, but not very well. Im guessing I need to start with the butterfly valve stop screw first, then the idle screw, then fuel mixture....right? My question is, Are there any settings to get me started? (ie. number of turns on each screw to get them all close). plz help

Dustin

Joes924Racer · Posted: Sat May 10, 2003 8:38 am Post subject:

Are you talking about the air fuel mixture screw
down in side the boot or just the throttle body stuff.?
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

mustbfaster2 · Posted: Sat May 10, 2003 8:50 am Post subject:

Both. The screw that adjusts the throttle plate AND the idle screw on the side of the throttle body are both off.

BTW Joe - I forgot to mention its an 80 931 if it makes a difference.

mustbfaster2 · Posted: Sat May 10, 2003 8:58 am Post subject:

Actually what I meant to say was all 3.

1. screw on mixture control unit
2. idle screw on throtthle body
3. stop screw for throttle plate

mustbfaster2 · Posted: Sat May 10, 2003 9:07 am Post subject:

Basically....I know Im in for a world of headaches on this one. Timing is probably a bit off too but from what Ive read idle speed affects timing. I just dont know where to start. This is a heck of a car to tune.

Joes924Racer · Posted: Sat May 10, 2003 9:36 am Post subject:

mix should be done by machine its a percentage thing air to fuel and the throttle stop and stuff come after, idle should be around 950 or 1000
then set timing with light. I have marks ground in dizzy hold down so I dont loose timing.You dont want to be running to rich or to lean with the mix.its best to go to a shop that can handle setting mix I wish I could remember the percentage theres a total percentage and just fuel
maybe someone will tell who knows Id have to make a call and Im out the door for the weekend as we speak so.

Later
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

mustbfaster2 · Posted: Sat May 10, 2003 9:48 am Post subject:

thanks Joe. I be working on it all night and probably tomorrow so ill let ya know where im at

Dustin

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

start idle at 2 1/2 turns out.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

Augidog,
What is that avitar? It's not part of your anatomy dressed as a puppet is it!
_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

my wifes idea. made me laugh.
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

Oiginaly posted by "gohim"

Adjusting the idle mixture isn't that hard to do. Some of you guys make it sound like it's a "Black Art".

First make sure that all the vacuum lines are in good condition, and none are disconnected or venting to the air.

If you have a later model with electronic idle stabilization, you need to disable it before trying to make any ignition timing, mixture or idle speed adjustments.

If the idle speed and mixture adjustments have been totally screwed up. Start from scratch. close the idle speed all the way down, then turn it out two complete turns.

Start the engine, adjust the idle mixture so the car will at least run well enough so it will warm up. Don't leave the allen wrech in the adjustment hole when you are checking the changes you have made. The weight of the wrench can influence the working of the throttle sensor plate. And don;t push down real hard for the same reason. The hole where the wrech goes in bleds enough air to throw the mixture adjustment off slightly, so you are going to want to reinstall the plug when you are done, and make a final check.

After the engine is warmed up, check to ignition timing first. Then set the idle speed. Then adjust the idle mixture from rich to lean making note of the range in which the adjustment can be rotated and the engine speed does not fall off, or rise significantly. Then set the mixture adjustment to the center of the range.

Check the idle speed. Is it correct?

If not, adjust the idle speed, then readjust the idle mixture adjustment to the center of the range.

Now blip the throttle. Does the engine speed rise smoothly, or bog down? If it bogs down, the mixture is too lean, and you need to adjust the mixture a little richer. Not too much, an 1/8 of a turn at a time can make a difference. I use an axtra long allen wrench, and pay attention to the handle at the top to keep track of how much I have rotated the adjustment.

Now go to the back of the car and look at the exhaust pipe. Can you see the exhaust coming out? What color is it? Blue smoke at idle, sorry, you have a worn engine. Black smoke, still too rich for some reason. Did you wait for the engine to warm up before starting? How does it smell? Like overheated metal? Bad cat, or too lean, maybe a cracked exhaust manifold. Does it smell like gas? Again too rich. Does your car have a O2 sensor? May be it's time for replacement.

See, that wasn't bad, was it?
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

augidog · Joined: 03 Mar 2003 Posts: 1360 Location: New Jersey

hey Roger/ I have no plug in mine . What can I use for a replacement? thanks
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

Roger · Joined: 06 Jan 2003 Posts: 1235 Location: Cordova, TN

Not sure. Mine is missing also the original has a wire so it can be removed and replaced. I will let you know if I ever figure it out.
_________________
1981 924 NA

Some people are like Slinkies. Not really good for anything, but you
still can't help but smile when you see one tumble down the stairs.

bryanc · Joined: 27 Feb 2003 Posts: 233 Location: San Antonio, Texas

The plug is no longer available from Porsche. If you are familiar with the "Help" line of products at the auto parts store they have a set of vacuum line plugs. One of those is close but a little too big. Put some spit on it and force it into the hole. After a few times it will go in easier.
As far as adjusting the mixture here is what I did and it seems to work.
Set the timing first. The screw which limits the throttle plate's motion has only one function, to keep the plate from wearing on the throttle body.
Set it so the throttle closes without wearing against the bore of the throttle body. The Haynes sugests you go from lean to rich. It's very easy to get excited when you are getting close to the correct setting (acceleration starts working correctly) Just get a piece of paper and keep track of each adjustment and how the car performed.
I agree with Roger. Adjust the screw 1/8th turn at a time.
If you accelerate at the 1st bit of gas pedal but then it flattens out and then accelerates at full throttle it is still too lean. Give it another 1/8th turn richer and try again. You may have to do this many times but if you keep track on paper you can always get back to the best performance.
_________________
'84 944
I'd rather have a bottle in front a' me than a frontal lobotomy
Tom Waits

mustbfaster2 · Posted: Wed May 14, 2003 3:12 pm Post subject:

Thanks for the help Roger. I'll give it a try and see how it goes. My car seems to be doing exactly what Bryanc was saying about runing lean. It accelerates at first then flattens out. One question for Bryan though is when I adjust the throttle plate screw, is it just to keep it from rubbing against the throtthe body or does it have to be open a bit to allow some air in for idle.