Bleed Screw Vs. Idle Stop Screw

[humanz 3]

Which one is for fine adjustments? Can't remember. Should the idle stop screw only be adjusted using the resistance values outlined in the Haynes manual, or can I give it a turn or two without the readings? It's a bit hard getting readings based on the angle of the throttle switch and the space between it and the radiator....

 

Should say that this is for an 8v Jetronic setup.

Edited June 8, 2010 by humanz

[MerlinGTI 3]

The brass screw on the TB is for adjustment of idle speed. The stop screw should be set and left alone really.

 

Settings for the stop screw are barely touching, then 4 full turns inwards off the top of my head. This sets the butterfly with a slight gap which I would expect is for lift off and idle purposes. Once the stop screw has been adjusted the TPS will need re-setting.

 

4 turns was a bit much for my car though, I put this down to the TB being 20 years old and the wear that goes with this. I ended up with about 2.5 turns in the end.

[humanz 3]

Thanks for the reply. "Never post when you are sleepy" is a lesson I've yet to learn. Merlin, I assume when you say TPS you mean the throttle switch, correct? I know the Haynes manual details using feeler blades to check the working of the throttle switch, but can you explain the "barely touching" and the "4 turns" parts? You mean you made stop screw barely touch the lever arm, then made 4 turns to "tighten" the screw, then adjusted the throttle switch as per the Haynes manual using feeler blades? This sounds like if I'm not careful, I could really mess things up.

 

My intention is to let a little more air into the throttle at idle. I find that the bleed screw doesn't allow me fine enough adjustments: right now, small quarter turns make little or no difference in idle speed, but after about a full turn, idle speed jumps like over 500rpm. I'd like an adjustment where I can get like a 100rpm increment. In fact, I think just an increase of 100rpm would be enough. So, should I use the stop screw? Or should I look elsewhere to fine tune idle speed?

[MerlinGTI 3]

If the bleed screw isnt allowing fine adjustments for you (100rpm adjustment should be a piece of cake) I reckon your throttle body could be gummed up with crud (very common).

 

I would give the TB a good clean with some carb/brake cleaner and some compressed air/Air line.

Completely unscrew the brass screw, clean this, clean the hole it goes into, clean all the barbs out, clean the butterfly... Everything really

 

 

can you explain the "barely touching" and the "4 turns" parts? You mean you made stop screw barely touch the lever arm, then made 4 turns to "tighten" the screw, then adjusted the throttle switch as per the Haynes manual using feeler blades? This sounds like if I'm not careful, I could really mess things up.

 

Ignore the TPS (throttle position sensor/throttle switch) for the moment Lets sort the stop screw....

 

Un hook the throttle cable from the reel on the TB. Pull the reel round a bit and let go. As it springs back on its own it will make a 'TINK' noise. This is the stop screw hitting the arm. If you unscrew the stop screw untill it no longer 'TINKS' the stop screw is no longer contacting the arm and the butterfly is fully closing.

With a quick bit of trial and error you can find the point where the stop screw is barely touching the arm. I think Haynes suggests using a feeler gauge for this but its a waste of time really, and very fiddley with the tb in the car.

Anyway, with the stop screw in the barely touching position, you then wind the stop screw in a full 4 turns (check the 4 turns bit in haynes its from memory. Im pretty sure its 4).

The butterfly is now set with a tiny gap when the throttle is off.

 

Now this is done you can adjust the TPS. The propper (long winded imo) way of doing this is in Haynes and involves feeler gauges.

I (and most others on here it seems) set them by backing off the 2x 7mm bolts holding it in place and rotating it so as the throttle fully closes the TPS makes a 'click' sound.

 

Any adjustments to idle speed now (and from now on) should be made on the brass bleed screw Will be worth getting your car on a gas analizer to set the fuel mixture now (allen head screw on the AFM).

 

You cant really muck anything up doing any of this. It is fiddley and a little time consuming. Problems start when you car has been adjusted incorrectly before in an attempt to cure a fault that exists elsewhere (air leak somewhere etc...)

 

Hope this helps and makes sence, I tend to ramble a bit

[welshpug 1,657]

Don't forget to slacken off the TPS screws before adjusting the throttle stop as it can prevent the throttle from returning fully.

 

4 turns is a pretty good rule of thumb and is the figure stated, obviously if its cammed you may need a little more or less.

[humanz 3]

Merlin:

Made sense, really. Just a couple things to clear up. Should the car be running when I spray the throttle body with carb/brake cleaner? Which is better (carb or brake cleaner), or are they equivalent? What are barbs? Rotate the TPS clockwise, or counter-clockwise?

 

Welshpug:

More turns = wider gap at idle? The engine does have a cam.

 

All sounds helpful. Will get the car into the garage tonite and give it a go. It's pouring here at the moment. The next step will be a gas analyzer, if the one here is still working. Cheers.

[welshpug 1,657]

yes, more turns = more air.

 

I would firstly see how it goes on 100% Haynes manual/factor settings though.

[MerlinGTI 3]

The barbs are the bits the pipes fit over

 

Clean the throttle boddy out with the engine off dude. If your not using compressed air (will make the job 100x easier) then cotton buds and a thinn peice of sturdy wire will do. poke it in all the barbs to un-block them.

 

Carb/brake cleaner are the same thing, some people call it brake cleaner some call it carb cleaner, some call it both

 

If you do take the TB out, be aware the bottom two barbs are for a coolant loop, so you will lose water.

 

Have some pics:

 

 

[humanz 3]

Ok, didn't have any carb/brake cleaner. Tried to set the stop screw to barely touching. It took twelve full turns to get the screw to be barely touching...me thinks..Wasn't very easy to tell when it was or wasn't touching...the lever sounded the same when i released the spring either way. So i turned until the screw was flush with the metal it's screwed into. So I turned it back first four times, then all the way back to twelve, plus one more turn. Will take it for a drive in a minute. This weekened I'll give the throttle a good cleaning out.