MFI start up circuit

[BSNMOE]

When starting a MFI the procedure cold is to pull up hand throttle and crank and when hot, gas pedal to floor and crank. Because this results in high RPMs for initial start, does this mean that the main rack influences initial start or is it the idle circuit because while cranking it's at a low RPM?

[matt demaria]

Fuel delivery is dependent on 2 things:
Throttle opening at the pump
And RPM.
Each variable moves the rack which delivers more fuel. That is why on cold start you use the hand throttle to move the pump linkage which moves the rack.
This does not include the thermo time switch network(s).
For a hot restart I usually just turn the engine over without throttle.

[Flieger]

The rack position is the only thing controlling the fuel to the engine other than the cold start squirters. The rack gets inputs from the throttle cable (which is connected to the foot throttle and which the hand throttle also can move), flyweights via the space cam (for rpm), shut-off solenoid, cold-start solenoid (if a 69), thermostat, and barometric cell.

[dicklague]

I got rid of the warm up regulator and un-hooked the solenoid to the squirters. I put in a relay that is actuated by a small push button on the dash that controls the cold start solenoid for the squirters.. Very easy to start when you are in control of the cold start squirters.

[BSNMOE]

Originally Posted by dicklague

I got rid of the warm up regulator and un-hooked the solenoid to the squirters. I put in a relay that is actuated by a small push button on the dash that controls the cold start solenoid for the squirters.. Very easy to start when you are in control of the cold start squirters.

How many times or how many seconds do you push the button? Also, do you push the button before or during cranking?

In the past I have noticed that the majority of the raw gas dumps into # 3 stack with # 2 and # 6 getting some and it appears that the rest get very little or none. It's the way the plumbing is arranged.

[tharbert]

Originally Posted by BSNMOE

How many times or how many seconds do you push the button? Also, do you push the button before or during cranking?

In the past I have noticed that the majority of the raw gas dumps into # 3 stack with # 2 and # 6 getting some and it appears that the rest get very little or none. It's the way the plumbing is arranged.

There is a check valve at the end of each squirter. This keeps the lines primed. If you have unequal delivery, chances are you have some gummed check valves. It's simple enough to disassemble, replace the fuel lines if needed and clean the valves but be careful as the check valves are unobtainium. I soaked my squirters in some solvent and ran them through an ultrasonic cleaner. They all work fine now.

Normally, if it's cold enough (I think I remember reading >50F) the bi-metal switch allows current to the cold start system while cranking. When the switch warms, it removes all power to the cold start circuit. So, use the button while cranking and then for only a few seconds. If you use it while not cranking, you are simply dumping gas behind the closed valve and liquid rather than vaporized fuel pours into the chamber. I don't think that's good.

[dicklague]

Originally Posted by BSNMOE

How many times or how many seconds do you push the button? Also, do you push the button before or during cranking?

In the past I have noticed that the majority of the raw gas dumps into # 3 stack with # 2 and # 6 getting some and it appears that the rest get very little or none. It's the way the plumbing is arranged.

I usually give it a squirt immediately before cranking and another when I am cranking. If the RPMs go down I give it another quick one.

All my nozzles seem to be working, but I will check them soon. I am also replacing the small fuel lines with some better stuff than the plastic I am using now.