I’ve always been dissatisfied with the amount of information describing Spica’s workings. So I’m the process of (flame suit on) doing a carb conversion. Now that I have it out of the car and apart I thought I’d try to describe how the Spcia works with some pics. Typical caveats I’m not an expert, no advice on turning, and this is for a T237 (1971 1750 motor) so yours might be differences.
The Spica is like a mini engine... crank, connecting rods, and pistons but pumps fuel rather than air. From the bottom, the crank and connecting arms and drive pully right.
![1636782]( "1636782")
To adjust the amount of fuel for each stroke there are rotational metering devices (brass colored) that are moved by a linear rack behind.
![1636781]( "1636781")
The most basic control of this rack is with rpm and throttle position. In general, there is a pivot (red) that that moves the rack (green) in and out. Note there is a short rod (yellow) with a ball on the end that rides on that dark conic. As that ball moves on the conic it causes the pivot to move changing the fueling.
![1636783]( "1636783")
The conic can move in two ways. Rotate via throttle position and in/out with rpm. The throttle log rod, through some arms, rotates the conic. Behind the conic is a part that rotates on the “crank shaft”. This holds 6 larger ball bearings in a cup. As rpms increase, centrifugal force moves the ball out and up the cup sides. This moves the whole conic section in and out. Note this motion is resisted by springs between the conic and throttle rotation device. Using different springs can change the rpm metering. Guessing, but stiffer would lean at higher rpm and softer would richen.
![1636784]( "1636784")
But there are 4 other mechanics that can change the rack motion in addition to this basic operation.
The mixture adjuster / de-accel. First, I lied. The linkage from the pivot doesn’t go directly to the rack. In reality it goes to another set of linkages. At the bottom (blue) is the attachment to the actual rack. There is a perpendicular linkage from this (red). Close to this is the link (green) going back to the pivot. The mixture adjuster pushes on an arm (not shown) and rotates a shaft (right view). Inside there is an offset shaft. If the green link is stationary and the yellow shaft rotates it will cause the rack (blue) to move in and out. So, as a mixture adjuster, and it’s screwed in/out, it slightly causes the rack to move in/out. As a de-accel cutoff, it makes a larger motion pushing the rack all the way in cutting off fuel. Note, since this is the last part in the linkages, changes here will be added to all other inputs.
![1636785]( "1636785")
Temperature setting lever / altitude compensator….
First note there are notches on the pivot and the link going to the rack links has a wire. Depending on which notch the wire is on it will change it will change the pivot arm length. Higher on the pivot arm, more motion, richer and the reverse lower. The temperature setting and altitude compensator are in series and act on a tab on the link between the pivot and rack links. As their length increase it will force the wire to engage a notch lower on the pivot arm causing a different rate of change in mixture. As the length shortens, a spring (see above) pulls the wire to a higher notch. Recall the initial length of the temperature setting and altitude compensator can be adjusted. This sets which notch the wire would naturally sit in and the rate of changing the mixture or leaning/enriching at higher rpms.
![1636786]( "1636786")
Cold start / Thermo Actuator (TC)
The pivot is really made up of two pieces. One with the ball on the conic and the other a “fork”. One side of the fork interfaces with the cold start / TC while the other has the notched arm for the link to the rack. The cold start/TC linkages are hard to explain but in short, they both act on the fork to move the rack.
Finally, a schematic trying to pull it all together...
![1636787]( "1636787")
I hope this helps.
PS it would be really cool if someone figured out how to do a electrically sensed and mechanically actuated system out of this. Gut the left side, add a throttle positioning sensor, rpm sensor, and add a linear actuator to move the rack. Add some other inputs, MAP/temp/AFR and it'd make a nice system.
The Spica is like a mini engine... crank, connecting rods, and pistons but pumps fuel rather than air. From the bottom, the crank and connecting arms and drive pully right.
To adjust the amount of fuel for each stroke there are rotational metering devices (brass colored) that are moved by a linear rack behind.
The most basic control of this rack is with rpm and throttle position. In general, there is a pivot (red) that that moves the rack (green) in and out. Note there is a short rod (yellow) with a ball on the end that rides on that dark conic. As that ball moves on the conic it causes the pivot to move changing the fueling.
The conic can move in two ways. Rotate via throttle position and in/out with rpm. The throttle log rod, through some arms, rotates the conic. Behind the conic is a part that rotates on the “crank shaft”. This holds 6 larger ball bearings in a cup. As rpms increase, centrifugal force moves the ball out and up the cup sides. This moves the whole conic section in and out. Note this motion is resisted by springs between the conic and throttle rotation device. Using different springs can change the rpm metering. Guessing, but stiffer would lean at higher rpm and softer would richen.
But there are 4 other mechanics that can change the rack motion in addition to this basic operation.
The mixture adjuster / de-accel. First, I lied. The linkage from the pivot doesn’t go directly to the rack. In reality it goes to another set of linkages. At the bottom (blue) is the attachment to the actual rack. There is a perpendicular linkage from this (red). Close to this is the link (green) going back to the pivot. The mixture adjuster pushes on an arm (not shown) and rotates a shaft (right view). Inside there is an offset shaft. If the green link is stationary and the yellow shaft rotates it will cause the rack (blue) to move in and out. So, as a mixture adjuster, and it’s screwed in/out, it slightly causes the rack to move in/out. As a de-accel cutoff, it makes a larger motion pushing the rack all the way in cutting off fuel. Note, since this is the last part in the linkages, changes here will be added to all other inputs.
Temperature setting lever / altitude compensator….
First note there are notches on the pivot and the link going to the rack links has a wire. Depending on which notch the wire is on it will change it will change the pivot arm length. Higher on the pivot arm, more motion, richer and the reverse lower. The temperature setting and altitude compensator are in series and act on a tab on the link between the pivot and rack links. As their length increase it will force the wire to engage a notch lower on the pivot arm causing a different rate of change in mixture. As the length shortens, a spring (see above) pulls the wire to a higher notch. Recall the initial length of the temperature setting and altitude compensator can be adjusted. This sets which notch the wire would naturally sit in and the rate of changing the mixture or leaning/enriching at higher rpms.
Cold start / Thermo Actuator (TC)
The pivot is really made up of two pieces. One with the ball on the conic and the other a “fork”. One side of the fork interfaces with the cold start / TC while the other has the notched arm for the link to the rack. The cold start/TC linkages are hard to explain but in short, they both act on the fork to move the rack.
Finally, a schematic trying to pull it all together...
I hope this helps.
PS it would be really cool if someone figured out how to do a electrically sensed and mechanically actuated system out of this. Gut the left side, add a throttle positioning sensor, rpm sensor, and add a linear actuator to move the rack. Add some other inputs, MAP/temp/AFR and it'd make a nice system.
