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914World.com _ 914World Garage _ Idle adjustment screw for D jet
Posted by: jsaum Jun 21 2011, 10:09 AM
I was helping Matteyp tune his car last night and it's the first time I have worked on a fuel injected engine. We got the dwell set and the engine timed with the light, it's running better but when I tried to adjust the idle speed the adjustment screw didn't seem to affect the idle speed I gave it two full turns in each directions. My questions is how sensitive should this adjustment be?
Jsaum
Posted by: r_towle Jun 21 2011, 10:13 AM
its an air bypass screw and its sensitive.
If it does nothing then you may have a vacuum leak, or several, or the TPS may be adjust wrong...or timing is off.
Rich
Posted by: matteyp Jun 21 2011, 10:51 AM
James did we have that vacuum line plugged when you were adjusting that screw?
Posted by: jsaum Jun 21 2011, 11:10 AM
James did we have that vacuum line plugged when you were adjusting that screw?
Yes, it was plugged, after we adjusted the timing I placed it back on. The last time we ran the motor I tried adjusting it. After you get the valve cover gaskets replaced I can come back over and we can try to dial it in a little better.
Jsaum
Posted by: windforfun Jun 21 2011, 11:12 AM
It's very sensitive.
Posted by: r_towle Jun 21 2011, 11:14 AM
what did you set the dwell to?
How did you set the timing?
How is the the action on the advance plates inside the distributor and does the vacuum advance canister hold a vacuum?
Do the plates move freely or get stuck in any position?
Rich
Posted by: Ian Stott Jun 21 2011, 11:59 AM
I adjusted my idle up last weekend, did it when the engine was warm, very little turn on the screw to take idle from 600 to 900/950. Maybe 5 degrees of a turn, very sensitive, but yes all the little vacumn leaks add up, make sure you address those before anything else.
Ian Stott
Moncton
Canada
Posted by: Drums66 Jun 21 2011, 11:59 AM
......vacuum leak?.....it is sensative! 
Posted by: Prospectfarms Jun 21 2011, 03:18 PM
It's very sensitive.
what did you set the dwell to?
How did you set the timing?
How is the the action on the advance plates inside the distributor and does the vacuum advance canister hold a vacuum?
Do the plates move freely or get stuck in any position?
Rich
I had no idea what the screw did to affect idle until I came across a diagram. If I understand it correctly, the screw changes the effective size the throttle chamber -- it looks like an adjustable carburetor throat. So, if turning the screw doesn't do anything either the motor's not in tune or there air leaking in somewhere.
I was told and recently learned first hand, that making sure the valves, time and dwell are in spec makes troubleshooting the rest of the fuel system so much easier.
Posted by: 76-914 Jun 21 2011, 08:46 PM
Also, with the breather off you should be able to hear the difference as the sound gets louder and quiter with changes in setting. It's like a whistle. 
Posted by: jsaum Jun 22 2011, 09:20 AM
what did you set the dwell to?
How did you set the timing?
How is the the action on the advance plates inside the distributor and does the vacuum advance canister hold a vacuum?
Do the plates move freely or get stuck in any position?
Rich
Dwell set at 44, timing at 3500 RPM on 28 degree mark. The engine idled much better, but we weren't able to get it to come down it's idling at 1000 to 1100 rpms. I think there may be some vacuum leak issues and possibly an exhaust leak he was getting a little bit of back firing or popping happening. He also has an oil leak from the valve cover gasket we could only run the car for about ten minutes before it would begin to smoke up the garage. The vac advance plates seem to be moving O.K.
Jsaum
Posted by: r_towle Jun 22 2011, 10:21 AM
48-52 is the dwell range....48 is the sweet spot.
52 is the acceptable tolerance, so shoot for 48
As the points get corroded the dwell increases because the gap actually gets smaller as the corrosion builds up over time.
Do look at the vacuum canister and try to set the idle with the hoses removed from the distributor and hoses plugged.
When I look for a vacuum leak I remove all hoses from the plenum except the MPS.
I cap all the hoses at the plenum with either rubber vacuum caps , or electrical tape.
I remove ALL systems.
Then set the idle.
After that...add ONE line at a time and retest.
You may find that your AARis leaking, the decel valve is leaking etc etc....
Rich
Posted by: 70-914nut Jun 22 2011, 06:00 PM
1.7 liter 3500 rpm@ 27 deg BTDC
Posted by: Cap'n Krusty Jun 22 2011, 07:49 PM
48-52 is the dwell range....48 is the sweet spot.
52 is the acceptable tolerance, so shoot for 48
As the points get corroded the dwell increases because the gap actually gets smaller as the corrosion builds up over time.
Do look at the vacuum canister and try to set the idle with the hoses removed from the distributor and hoses plugged.
When I look for a vacuum leak I remove all hoses from the plenum except the MPS.
I cap all the hoses at the plenum with either rubber vacuum caps , or electrical tape.
I remove ALL systems.
Then set the idle.
After that...add ONE line at a time and retest.
You may find that your AARis leaking, the decel valve is leaking etc etc....
Rich
Actually, the dwell spec is 47 +/- 3 degrees. 52 is far too high, meaning the point gap would be too small. Setting them that way means they'll close up even more, and your dwell might end up around 60.
The Cap'n
Posted by: r_towle Jun 22 2011, 08:01 PM
Its like me and my shadow.
So happy you get up each day so you can ensure you find any thread I post in and make your points, and 40 years of experience, well known.
I know it makes you feel good so I am glad to have served that purpose for you each and every day.
Its adds so much value to my day, I would miss the interaction.
Rich
Posted by: 76-914 Jun 22 2011, 10:34 PM
48-52 is the dwell range....48 is the sweet spot.
52 is the acceptable tolerance, so shoot for 48
As the points get corroded the dwell increases because the gap actually gets smaller as the corrosion builds up over time.
Do look at the vacuum canister and try to set the idle with the hoses removed from the distributor and hoses plugged.
When I look for a vacuum leak I remove all hoses from the plenum except the MPS.
I cap all the hoses at the plenum with either rubber vacuum caps , or electrical tape.
I remove ALL systems.
Then set the idle.
After that...add ONE line at a time and retest.
You may find that your AARis leaking, the decel valve is leaking etc etc....
Rich
You taught me that over a year ago. It's worked twice. 
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