Vacuum Gauge Connection

[Nic J]

Hi,

I bought myself a vacuum gauge to tune my idle speed however I can't find a connection for the port (4mm grub screw) in the venutri.  I have read about the possibility to get a M4 thread to hose barb screw however I can seem to find one on the internet. 

How do you all connect your gauges I'm concerned that I need a really good connection or the gauge will read incorrectly?

Kind Regards,

Nic

[J. Huber]

Hey Nic. On my 230SL the screw is here... Be very careful not to drop that little guy. Good luck.

[Nic J]

Thanks,

How do you connect your vacuum gauge once the screw has been removed, I can't seem to find an adaptor?

Cheers,

Nic

[J. Huber]

Mine came with a small pointed connector. It fits in the hole but initially wanted to pop out. So I twisted it in a bit which gave it almost a thread. So it now stays put if I'm careful.

PS I just reread your initial post -- you weren't asking for the port but for a connector? Sorry if I had that wrong.

[Nic J]

Thanks,

I shall try whittling down the cone connector and screw it into the hole.

I have been looking for a 4mm thread to barb connector on the old Internet but it seems google does not care about us 230 owners trying to tune our idle

Thanks again,

Nic

[stickandrudderman]

Why do you want a vacuum guage to tune your idle speed?
A vacuum guage is an excellent indicator of engine condition however, and if you want to check that then you need to buy a small vacuum take-off fitting that screws to the back of the inlet manifold on 116/117 engines.(V8 from 80s) Then you can screw it into your manifold and connect your vacuum guage to it.
Works a treat!

[Larry & Norma]

I drilled a hole thro a 4mm bolt, filed down the end 'til the tube fitted over. Job done!

[Nic J]

Thanks for all the replies,

I thought the correct way to set up the warm idle is to use a vacuum gauge to set the Idle Air Screw (max vacuum) then the Idle Fuel screw to get the correct combination for smooth Idle and correct Idle RPM?

When I bought my car it was idling either too fast or too slow it was all over the place and was not idling very smooth.  By ear I have the car running at the correct RPM and nice and stable, it no longer cuts out when shifting into neutral or between drive and reverse however it is still not as smooth as I would like so I shall have a play at the weekend with the gauge connected.  I also need to take a look at the cold start setup, she starts fine and the cold start mechanism is working but I have to use a little gas for the first start in the morning, I think they should start with a full press on the accelerator then turn the key with no gas?

From reading this board and the workshop manuals the idle and linkage setup is crucial to a smooth running car, it can affect all sorts from smooth transmission shifting etc.  I have not worked on an automatic car before let alone one with fuel injection I was surprised to see just how smoother the box shifted after setting things up a little.  Next step is to check the butterfly in the Ventury is closed at idle as I suspect the idle stop might have been adjusted to control the idle speed.  The valves and tappets are supposed to have been just adjusted on my car before I bought it and it drives beautifully however a little diagnostic can't hurt.

For a 45 year old car these Mercs are amazing, I can't wait for some warmth to get the roof down.

Thanks again

Nic

[J. Huber]

Thanks for all the replies,

I thought the correct way to set up the warm idle is to use a vacuum gauge to set the Idle Air Screw (max vacuum) then the Idle Fuel screw to get the correct combination for smooth Idle and correct Idle RPM?
...

Nic

Yes I agree. First though are: getting the linkage set perfectly, then having your points and timing set and confirming the plugs are in good order. Then I would use the Vacuum gauge to get the Idle air to the best highest point for RPMS, then go to Fuel screw. Somewhere in the Tech manual is George Davis' explanation which is excellent.

[Nic J]

I spent a little time fiddling this weekend, and after a couple of checks I noticed that the Venturi butterfly was not closing fully.   I was hoping that the ventrui stop had just been incorrectly adjusted and that the other linkages were all OK.  After adjusting the Venturi stop the Idle was great but when drive was engaged the engine stalled.

Looks like its time to plow through the linkage tour (http://www.sl113.org/forums/index.php?topic=5003.0) and get her setup correctly.

I did however get my Vacuum gauge connected however the gauge read late timing,  I shall check this again after I have set up the linkages.

Thanks,

Nic