Help again! 1974 needs priming to start

[mark944T]

My 1974 2.7L that had been sitting for six years got running because of help from people in this forum. The problem though is it will not start when cold without turning on the pump, taking the air box cover off and filter and pushing up on the flap inside the air box which you hear a slight squeal which puts gas into the cylinders.

It will start normally when warm but I need to do the above procedure when cold. I’ve tried letting the pump run for about 15 seconds when cold but that didn’t work.

Thanks

[Flat6pac]

You’re not holding residule pressure in the injection system
Replace the check valve Banjo fitting on the pump.
Bruce

[mark944T]

Originally Posted by Flat6pac

You’re not holding residule pressure in the injection system
Replace the check valve Banjo fitting on the pump.
Bruce

I see this for sale on Pelicans. Is this right?

https://www.pelicanparts.com/More_Info/91160890100.htm?pn=911-608-901-00-OEM&SVSVSI=13193&DID=39725

[Zaz]

Sort through your cold start circuit - hand throttle/micro switch, thermo time switch, cold start valve and WUR.

[mark944T]

Originally Posted by Zaz

Sort through your cold start circuit - hand throttle/micro switch, thermo time switch, cold start valve and WUR.

I am not that familiar with these cars so I have no idea what sorting through all those parts entails. I looked in WUR last time and didn't see any problems and hand throttle works. The rest I have no idea but I'll need to do some research.

Anybody else? Thanks

[boyt911sc]

Originally Posted by mark944T

I am not that familiar with these cars so I have no idea what sorting through all those parts entails. I looked in WUR last time and didn't see any problems and hand throttle works. The rest I have no idea but I'll need to do some research.

Anybody else? Thanks

Mark,

You need to use a fuel pressure gauge to do a fuel injection troubleshooting. Otherwise, you will be just doing guess-work troubleshooting. You need to measure and test your cold control pressure. Have you tested and confirmed that the CSV is working? If you don’t have a fuel pressure gauge kit, borrow or get one. Otherwise, you will spend a lot of your time chasing your tail.

Tony

[Walter_Middie]

You are using the hand throttle pulled up about half way when starting? This energizes the cold start valve, which runs when the key is in the start position and the car is cold.

The thermo time switch is on the driver side cam cover and decided whether or not the car is warm or cold and sends power to the cold start valve when needed.

The cold start valve is an extra injector inside the intake that adds fuel during starting - just like when you add fuel through the throttle plenum or lifting up on the air flow plate to run the injectors.

It sounds like the cold start valve is not firing.

[mark944T]

I have another 1974 911 that starts with just a turn of the key, no hand throttle needed. Sounds like I need to test the CSV. I'll need to learn how to do that. Can I bypass and will it start? Is there an easy way to access the CSV?

[Walter_Middie]

The CSV is well hidden at the front of the engine where the trans attaches. It is hard to get to. I'd start with testing the thermo-time switch, as this is really easy to get to. Here's some notes I copied from a previous post:

While the key is in the run position, power will be sent to the CSV if the Thermo-Time Switch and throttle switch allows it. On the left side chain cover is the Thermo-Time Switch which is the basic control for the enrichment solenoid during the starting phase. If the car is warm from running recently, or enough time has elapsed since it was started, the Thermo-Time Switch will interrupt the power going to the CSV.

Cold start valve circuit: There should be a wire (yellow) from the ignition switch to terminal 50 on the starter, from terminal 50 of the starter a wire (yellow) goes to the throttle valve switch. From the other side of the throttle valve switch a wire (also yellow) goes to the thermo-time switch on the driver's side chain case, this wire from the throttle switch attaches to one terminal (this is the non-ground side terminal) of the thermo-time switch, a second wire (gray and white) is also attached to this same terminal of the thermo-time switch and goes to the cold start valve. From the other side (ground side) of the thermo-time switch a second wire (red and black) goes to the cold start valve.
The cold start valve has both wires coming from the thermo-time switch. It’s the ground side that is interrupted when the engine is warm (or you run the starter for more than 8 seconds). You should have power to the yellow wire anytime the starter is engaged, and the throttle is slightly open (hand throttle).

[mark944T]

This will take some time.

[fintstone]

Originally Posted by mark944T

I have another 1974 911 that starts with just a turn of the key, no hand throttle needed. Sounds like I need to test the CSV. I'll need to learn how to do that. Can I bypass and will it start? Is there an easy way to access the CSV?

If it does, it has been modified or something is wrong with it (too rich).

For a '74, a common problem is the hand throttle has a plastic piece under the shifter that breaks. Also, the 7th injector (csv) on the back of the engine is critical for starting. That has to work right...or real hard starting. It is hard to reach with the engine in the car. Most folks do a partial drop to work on it...but I did not.