MFI Cold Start Fire Danger?

[bobmagyar]

It has been expressed that there is a danger with fire due to the design of the 69-71 MFI cold start system. I am wondering what the failure mode is that causes the fire.

Leaking Lines?
Sticking Valve?

Since I am restoring my car to original and live in a colder climate I wish to use the original system and would like to pay close attention to or replace all the components that could cause problems. For anyone else this would be a good checklist.

Can someone also explain what actuates this system as it is not mechanically linked to the hand throttle.

Thanks.

[pu911rsr]

Bob,
Not sure of the mechanism but I owned a 69 E that had cold start disconnected, when I sold car new owner reconnented and you guessed it he toasted car. My 69 S has cold start disconnected and it is a pita to start cold.
Phil

[Bobboloo]

Hi Bob,

There's a thermotime switch located on the crankcase breather cover. When the motor is below a certain temperature i.e. (cold) it allows current, when cranking to the cold start solenoid located on top of the fuel filter for a period of about 2 sec. this opens the valve and fuel flows through the small hose to the airbox and sprays fuel into the stack.

The valves can get stuck open or closed and cause their respective problems. A fire can get started by a backfire or just old leaky fuel lines.

As long as your lines and the solenoid are good there should be no problem. Maybe using metal horns on your stacks might also be a good idea.

edit:

The cold start system changed in 70'. It was simplified a little from the 69' setup.

edit#2:

I just remembered. Make sure your cold start solenoid doesn't have a crack in it. I just remembered that the 72' Coupe I used to have had a cracked one. If you cranked the car with the cold start setup enabled it would spray fuel right on top of the CDI. I quickly remedied the situation with a replacement.

I'll also take the opportunity to suggest that anyone reading this post make sure they have a fire extinguisher at all times in their early car. There are many ways these old cars can go up in flames.

[bobmagyar]

Thanks Bobby,

So I guess the failure modes can be:

Thermo-time switch that continually sends current to the soleniod valve and floods top of engine.

Leaky fuel lines.

Sticking or leaking solenoid.

So if one renews or inspects these components then this system should be reliable and safe?

[spydr32000]

Usually if the cold start solenoid hose is off, perished or damaged that is about the only time your likely to risk fire damage with MFI

[raspy2point2]

Also plastic air cleaner assembly's were used on 1971 911s and unaware techs would not be carfull and break the little fuel spray lines to the stacks when removing or attaching the air cleaner assembly and when started gas goes over the side of the stacks and sometimes onto a hot engine. It was all plastic ;the 1970 and 1969 cars were still metal housings. Regards Chris 70S R-Gruppe#144 Early S#205

[pwd72s]

With the 2.4 models the factory wised up a bit...the cold start system sprays the fuel in through fittings low down inside the stacks...much safer.

[schmidt]

If the car doesnt start, quite trying, the cold start circuit has about a 5-7 second cycle time every time you are trying to start a cold engine every time you turn the key to the start position, only the thermal switch once the engine warms up will deactive the system. This could cause a problem on ANY year car regardless of where the cold start nozzles are located with flooding, hydro lock and fire.

Jeff Smith
Schmidt Foreign

[blue72s]

I know this is a very old thread but can the 2.4 MFI cold start system be retrofitted to 2.2 models?

Thanks in advance.

[edmayo]

Only if you can figure a way to install the 72-73 style spray bars in the earlier style metal air stacks. I've never seen it done. With the earlier system the best you can do is make sure you have the metal air horns, and that the spray bar in the aircleaner is spraying a good stream directly downward into the stacks, and not dribbling off to the side. It was the plastic air horns that led to most of the fire problems.