'75 911s starting problem

[Gumba44]

Have a consistent cold starting the motor problem. Have done the pop-offs, timing, ignition, fuel lines, filter, etc,. Aaron suggests the FUEL Accumulator or the WUR cold pressure. I'm constantly adjusting the throttle lever to get the right mix, resulting in long delays between cranking and starting.

In addition, Aaron states that system pressures dictate everything. If they are not within specs then there is an issue. Some people adjust the WUR to alter the system pressures but he believe's they are working around the real problem, like the fuel distributor may need servicing or the WUR is requiring recalibration, or both. Then there are air leaks. That system has a great deal of potential leaks.

Anybody want to weigh in on this discussion???? These adjustments are beyond my DIY pay grade.

[75 911s]

Once it runs, does it run fine? Like idle at 950 and sound healthy?

Just trying to verify if it's a cold start problem only. If it is, then you can narrow potential issues.

the CSV is operated by the thermo-time switch. At 34degrees C it creates an earth(ground) to the CSV allowing extra fuel to be injected directly into the back of the air box. Make sure your thermotime switch is connected. It's located on the left front chain box and has two spade connections.

A lead from the starter is connected to the Thermotime switch and after a short time, heats the element inside, breaking the earth to the CSV, making it stop.

You mention a litany of other problems, like air leaks and such. Air leaks don't normally factor all that much into cold start problems, just crappy running after the fact.

The WUR creates a low pressure above the plunger when the engine is cold. This allows the plunger to raise easier and thus, more fuel is injected via all the injectors while the WUR is open.

As for the throttle arm in the cockpit, I raise mine, start the car, and then adjust to about a 2k rpm to let the car warm up. After about 20 seconds to less than a minute, you can drop it and the car should idle normal. As a 75, this is your auxilary air valve in a way (since later cars have an AAV and ours don't)

Once you get it warm, and the throttle arm is completely lowered, you should be at 950 idle.

Good luck.