Zenith High Idle

[project 911]

Well, I’ve been rebuilding this car for nearly four years now, and I’m finally on the road regularly. There are a couple of details that I need to fix before I go crazy.

Background:
1970 2.2T motor w/Zeniths – Stock as far as I know

Problem:

Zeniths-
When I start the car cold, I can use the hand throttle to get it smoothed out, and adjust the idle down low (under 500 using the idle screws) and it will sit there and idle beautifully for quite some time. Then without touching anything, the idle will rev up to about 1900 and stay there forever. Occasionally it will drop back down in traffic around town, but mostly just stays up. I’m working through the usual popping and spitting, but the idle thing is making me nuts.

What’s been done:
The carbs are clean (soaked, sprayed, disassembled, blown out). The shafts seem tight. Can’t find any vacuum leaks. The microswitch that activates at idle position is working properly. The enrichment solenoid clicks when power is applied. I have an extra set of carbs, so every part has been swapped out at some point to get the best bits. No hang-up with the linkage. All barrels have been ballanced using my syncrometer.

If I unhook the microswitch and/or enrichment solenoid- No difference
If I unhook and plug all the Auxiliary enrichment setup- No difference

So, what could be causing this rise in idle speed? Is some function adding fuel, or adding air? Where else can I look for a solution? (yes, I’ve used the search function).

Any suggestions would be very welcome.

[si2t3m]

I'll make a guess:

Sticky or weak springs in the distributor?

Marc-André

[project 911]

I've been wondering about that. I have the Marelli distributor, and it seems to be in good shape with no shaft play. The weights move smoothly, but I've always thought the springs seemed wimpy. I didn't know that they can get weak. Wonder where you'd get new ones???
I think I'll keep a timing light on it to see if it advaces when the idle goes up.

Thanks for suggestion-

[Allenk]

[QUOTE]Originally posted by project 911
[B]

"When I start the car cold, I can use the hand throttle to get it smoothed out, and adjust the idle down low (under 500 using the idle screws)."

I don't understand? What are your air mixture screws set at? It sounds to me like your adjustments are off. Here's what happened to me- My needle valves were leaking past due to ???? but any way, I had nearly no adjustment at my mixture screws, buy could get a good idle-just rich. So I would turn in the mixture screw trying to lean it out a bit. PROBLEM- once I gave any additional fuel, the car would hold at a high rpm because the secondary circuit would kick in and the leaking needle valves supplied the added fuel . It would occassionally return to idle if the engine began to get flooded. I could tell the needles where leaking when I turned the engine off and listened into the throttle bodies and could hear fuel girgle as the pressure was releived from the fuel system. Just one persons Zenith experience but just a note-I started my car for the first time this year last weekend and my needles are stuck again-time to clean the fuel system no doubt.

[project 911]

Marc-André -

You may win the prize! Just took out the thermostat and found it stuck open. I'm about to take a test drive with the replacement and see what happens.

Thanks for the idea.

[project 911]

Oops... replied to the wrong post. Must be all the gas fumes.

Allenk-

I've had the same problem (I think), but I seem to be getting it sorted out a little at a time. At least the plugs look good now. I opened them up again today and replaced a couple of O-rings. It amazes me how the slightest little change can mke such a big difference. It seemed like an extra 50 horses after todays tweaks, but I still have the idle all over the place. Mixture screws are all 2 - 2&1/2 turns out. It ran great today, but then later on acted like it was running on 4 cylinders when I punch it.
Guess I'll just keep trying.

[Allenk]

The biggest problem I've had with sharp pedal movements is getting the dang accelerator jets to all squirt properly. It seems just as I get them all cleaned and flowing right, one decides to act up. Even after rbuilding the pumps etc. I wonder if that isn't your problem. That would result in a fuel starved motor on sharp accleration and a few good pops from the carbs.

[project 911]

Allenk-

I agree, those things are a real pain, with no good way to clean them out. I just replaced some of the o-rings on them yesterday, and it helped a couple of the leaky ones, but one got plugged up again. I also tried to adjust them to all squirt the same volume, but didn't have much luck. You may be right that one or more gets plugged and makes trouble. It sure runs better out on the road, or under harder driving. It doesn't like being stuck in traffic around town.

I'll keep tweaking...

[Allenk]

I've soaked mine in parts cleaner and blown the cleaner through witn air and it's helped alot but the fuel sytem must be clean and I need to do some work there.