MFI Cold Start Questions - Any Help?

[Gary R]

My cold start does not work on my 1970 911E Targa the mechanic that worked on it by-passed the "cold start selenoid" (I believe it is on the top of the pump on the left hand side of the engine compartment). I would like to get the cold start to work correctly. I have found a person who has one (with the pump unit). I have a few questions that I need help with:

First, what is the correct name for what I am calling a selenoid (the unit that actually responsible for sending a quirt of gas down the intake to assist in cold starts)?

Secondly, what is a good way to see if the used on is good or not?

Third, what is a fair price for a used one?

Where can I get a new one if necessary and what should I expect to pay/

I know I asked a lot of questions, thanks in advance for the help.

Gary R
1970 811E Targa #933

[304065]

Gary,

It is a solenoid, which is a fancy name for an electromagnetic valve.

Your '70E cold start system is the same as the one in my 71E, consisting of the solenoid and some small diameter braided fuel lines running to a pair of brass manifolds installed in the air cleaner.

When the starter is cranking (yellow wire energized) AND the cold start switch is closed (this happens under certain temperature conditions which are outlined in CMA) the solenoid is energized and raw fuel dumps from the MFI filter console into the lines and into the brass manfolds. Three pinholes in the manifolds spray fuel down into the stacks.

That's how it is supposed to work. In practice the manifolds end up pissing fuel over the side due to misalignment, which can cause a fire. This is why most of these cold start systems have been ditched. Some people install a button on the dash to actuate the solenoid, but in my opinion all this does is require manual control over a system that should be automatic, somewhat of a retrograde step.

If I were you I would consider an alternative solution. This might include drilling a small hole in the MFI air cleaner base plate to accept a piece of hard brake line with a lock nut on the flare fitting, with a 180 degree bend in the line and the end clipped off and sticking down into the stack itself. This would localize the spray to the stack, a better solution than the brass manifolds up top. One per side should be enough for a cold start I would think.

The other alternative is to use a cable-operated enrichment device mounted in place of the MFI thermostat. Under ordinary operation the thermostat discs have heated to the point where they push the rod out into the pump (remember when it gets HOT it gets LONGER) and lean the mixture out. The cable device simply replicates this manually, allowing you to make the mixture around 10:1 AFR for starting-- you richen it up, crank with the throttle closed to suck in the mixure, then open to half throttle and it should bark to life, then you keep it rich for a bit then pull the cable and lock it to simulate the "long" position of the thermostat rod.

72 and later cars had internal pissers in the stacks themselves.

[Gary R]

Thanks John for the input.

I have owned the car since 1980 and I believe the car to be numbers correct. I like the idea of changing to internal pissers. It just seems to be a much better way of spraying for cold starts. If I were to do that, do you think it would significantly lessen the value of the car?

I had to change the front suspension in the late 80's when the left side of the "E" suspension gave out (I still have the "E" suspension). The car has an "S" front suspension now, but other than that the car is correct. I don't show it any longer, I just enjoy driving it these days

Thanks again for the help

Cordially,

Gary

[304065]

Gary,

I wouldn't be concerned about diminishing the value as long as you retain the original, unmolested pieces. Drilling a hole in the aircleaner base is a fairly simple operation and those bases are pretty common, so you could even source a replacement and do the work to that. Of course if you drill through the stacks or the throttle bodies that is not a reversible operation, so I don't recommend it.

Converting to 72- stacks is certainly an option but an expensive one and is an immediate aesthetic difference, the throttle bodies are slightly different and the stacks are hard plastic, vs. the magnesium of the early cars.

You might call Matt Blast at Eurometrix and see what he recommends for cold-start.

[Gary R]

Thanks again John. I think I am going to take your advice. Best of luck to you as well.

Gary
1970 911E Targa #933