Maybe a picture is worth a thousand words...
Here is my MFI pump, minus the cold start solenoid and thermostat. The upper right trapezoidal shaped block off plate with the allen screw in it replaces the thermostat, the one with all of the discs in it that has the hose to the left heat exchanger. Those of us that remove this troublesome thermostat replace it with this simple adjustment screw, or with a lever and cable arrangement that can be actuated from the driver's seat.
http://forums.pelicanparts.com/uploa...1549514650.JPG
Whichever one you have, the screw or plunger in its forward most position (screwed all the way in) represents the leanest, or the warmed up and running position. Backing the screw out, or actuating the cable to allow the plunger to move aft, will richen the mixture for cold starting. NEVER, I repeat NEVER use this adjustment as a general, overall mixture adjustment. That is not what it is for.
Even with this adjustment at full rich (backed all the way out), that is still not going to provide enough fuel delivery to start a cold motor. That is where the bypass solenoid comes in. This solenoid is not located on the MFI pump, but rather on the top of the filter console, at the forward left of the engine bay. It will have a wire connected to the top of it.
It is this "bypass" solenoid that is tripped by the thermal/time switch when you first turn the ignition key. With the electric fuel pump running, this "bypass" solenoid keeps the fuel from entering the filter console to be delivered to the MFI pump. It blocks that delivery and instead routs the fuel to the priming nozzles located in the air cleaner housing (early magnesium stacks) or the sides of the stacks themselves (later plastic stacks). When this solenoid is tripped, raw fuel simply sprays through these priming nozzles into the stacks. A lot like pumping the accelerator pumps on carbs - the motor is being primed by raw fuel.
This is all well and good when it works. It almost never does. The thermal/time switch receives current directly from the hot lead from the starter solenoid to the starter. This current heats it up. When the thermal/time switch is cold, it sends current to that bypass solenoid which makes it fire, directing fuel to the priming nozzles. When hot - either through warmed up engine heat or by the current it receives from the starter - the thermal/time switch shuts off current to that bypass solenoid, shutting it off in turn, and redirecting fuel to the MFI pump. If this happens too soon, there is not enough fuel to prime the motor for starting. If it goes on too long, it floods it.
Many of us get tired of that crap and simply wire the bypass solenoid to a momentary contact switch that we put somewhere on the dash. Now we have complete control over how much priming fuel gets delivered. That is what your car has. That's a good thing.
Most cars, when stone cold, will take about four to five seconds with your finger on that switch to fire the bypass solenoid. Turn the key to where you hear the electric pump running, but stop short of engaging the starter motor. Hold the bypass solenoid button down for four to five seconds. Pull the floor throttle all the way up and, for God's sake, keep your foot off the gas. Stepping on the gas pedal will often cause the cheap ass little plastic arm in the transmission tunnel that pushes on the throttle rod to slip off of the part swaged onto that throttle rod. Watch the gas pedal - make sure it moves downward a bit when you pull up on the floor throttle. If it doesn't, that cheap ass little plastic piece is broken. If that's the case, you are allowed to step on the gas pedal. No more than quarter throttle.
This will make your motor start reliably when cold. I promise. When warm, luke warm, hot, or whatever, you will have to determine, through practice, how long to hold down that button that fires the bypass solenoid, and how much floor throttle to pull up. Both decrease with engine temperature. When in doubt, more fuel and more floor throttle is usually the right approach.
Edit: Most of us simply leave the adjustment screw that replaces the thermostat screwed all the way in, all the time. Even up here in the Pacific Northwest, on our coldest days, my car will start easily without any need to fiddle with this screw. When I first installed it, I would religiously back it out to richen the mix for cold starts, let it run for awhile, and screw it in to the full lean running position. I eventually gave that up and now never use it. It just stays screwed all the way in. The floor throttle and bypass button on the dash are more than enough to start it in the coldest weather.
