Final tune, Need help Options

[Morph914]

Ok , so I have the engine running but it needs tuning. A little background, rebuilt stock 2.0 with D Jet, running a 123 dizzy. It fires right up and idles a little rough at first then smooths out. It revs fairly well and sounds good. The problem starts under load, it starts to stutter a bit.
I have not messed with the adjustment screw on the ECU or tried adjusting the throttle position sensor, or been able to check my fuel pressure.
I’m hoping to rally any troops in the north Florida area to help me get these final details ironed out.

Thanks in advance,
John

[emerygt350]

No kidding. Looks like new. Maybe better.

1 should be fine as long as the port on the distributor isn't going anywhere. Is there a vacuum line on the dizzy? It may not have a port, depends on the model of 123.

[Morph914]

No kidding. Looks like new. Maybe better.

1 should be fine as long as the port on the distributor isn't going anywhere. Is there a vacuum line on the dizzy? It may not have a port, depends on the model of 123.

There is a port on the dizzy, I have been experimenting with it on and off, seems to run better with it off.
The engine is an early ‘73 2.0, it originally had a 1.7

[JamesM]

There is a port on the dizzy, I have been experimenting with it on and off, seems to run better with it off.
The engine is an early ‘73 2.0, it originally had a 1.7

Its probably running better with it off as the 123dizzy should be retarding rather than advancing the timing on vacuum. On a stock setup the vacuum retards the timing at idle and overrun.

Timing should be checked with the vac line disconnected @ 3500 RPM to the 27 deg mark on the fan.

Set the 123 to the A or B curve and make sure the port it is connected to is below the throttle plate, the port that is seeing vacuum at idle. This will most likely cause your idle speed to drop quite a bit which you will need to compensate for by opening the air bypass screw on the throttle body which will then also probably require a minor adjustment to your idle mixture knob as well.

This may help your cold idle as well but...

You mentioned your motor is an early 73, looks like your airbox isnt though so it makes me wonder if you may have other part mismatches going on. Early 73 2.0s I find are a little more temperamental when it comes to parts as they were a very unique setup (hack) from the factory and the temperature curve on the sensor is very different than all other years. Need to be sure your MPS, ECU, and Head Temp Sensor all match for the year, either 73 or 74 and that if they are 73 you also need to be sure you have the inline resistor to the head temp sensor.

[emerygt350]

There is a port on the dizzy, I have been experimenting with it on and off, seems to run better with it off.
The engine is an early ‘73 2.0, it originally had a 1.7

Its probably running better with it off as the 123dizzy should be retarding rather than advancing the timing on vacuum. On a stock setup the vacuum retards the timing at idle and overrun.

Timing should be checked with the vac line disconnected @ 3500 RPM to the 27 deg mark on the fan.

Set the 123 to the A or B curve and make sure the port it is connected to is below the throttle plate, the port that is seeing vacuum at idle. This will most likely cause your idle speed to drop quite a bit which you will need to compensate for by opening the air bypass screw on the throttle body which will then also probably require a minor adjustment to your idle mixture knob as well.

This may help you cold idle as well but...

You mentioned your motor is an early 73, looks like your airbox isnt though so it makes me wonder if you may have other part mismatches going on. Early 73 2.0s I find are a little more temperamental when it comes to parts as they were a very unique setup (hack) from the factory and the temperature curve on the sensor is very different than all other years. Need to be sure your MPS, ECU, and Head Temp Sensor all match for the year, either 73 or 74 and that if they are 73 you also need to be sure you have the inline resistor to the head temp sensor.

Yikes, yeah, hopefully it is just the snorkel. I saw that strange plugged port and wondered about that. A quick look at the CHT for a resistor in line might help, so would a look a the ECUs number. I think I would get the number off the block, check the CHT, and check the computer. Does it have a PCV valve or is it passive? All of those things will help determine what you are working with.

James, 73 had retard and advance on the 009, it's choose your own adventure with the 123. You can go for #1 and hook it to the ported vacuum or put it on A and go for the retard port. Unless you are having issues with a high idle, there is no reason to mess with the retard side of things.

[JamesM]

James, 73 had retard and advance on the 009, it's choose your own adventure with the 123. You can go for #1 and hook it to the ported vacuum or put it on A and go for the retard port. Unless you are having issues with a high idle, there is no reason to mess with the retard side of things.

The 73 did have both but the advance side does very little and is also somewhat counteracted by the retard side as they are the same vacuum can. At best it was helping to overcome mechanical resistance and pull back the timing retard quicker at throttle tip in. It was never intended to run as advance only and the necessity to overcome mechanical resistance is moot on the 123dizzy as it is fully electronic, the "vacuum" port is just a map sensor so any response is already instantaneous.

Having tuned 914s with Megasquirt for close to 20 years now I can say that the range of both timing and AFRs that they will run under without noticeable drivability issue is pretty staggering, but the "optimal" window is far narrower and may not be known until you throw your car on a dyno or a smog machine, or even over a 10,000 ft mountain pass. I am assuming you dont get your car smog checked? Over advancing the timing may give the impression that the motor is more responsive as it is essentially ramping up the advance faster in the lower RPM range however 36-37 degrees advance is pretty far out from where stock type 4s are known to make their best power when optimized at WOT. Its also worth noting that as changing to timing impacts fueling requirements it is possible that the fact you feel its running best with that much advance may be an indicator that it is masking/compensating for an issue with your injection.