Something tells me you've some experience in this area 356RS!

Is there any difference in fuel delivery due to adjusting the #2 and #3 screws? Or maybe movement of the fuel delivery curve higher or lower in the RPM range when these screws are adjusted?

The best way to explain this is to show you what is happening to the "sensor" that is riding on the space cam. Remember, the job of the 3 springs in the "spring governor capsule" is to follow the contours/mapping on the space cam at different throttle & RPM's. The throttle controls the left and right movement of the space cam, and the RPM's control the fore & aft movement with help from the 3 springs and flyweights.
Photo below shows the sensor "U" following the mapping contour. The low tracks on the space cams cause the sensor lever to move the main rack forward and that causes the plungers to turn CCW on the left side of the rack and CW on the right side, turning the plungers toward more fuel delivery. If the sensor is adjusted so to cause it follow up the side of a contour, the rack moves the opposite direction and turns the plungers toward less fuel delivery, and goes lean. So you can see for example, the "E" space cam, if you adjust the #3 screws in CW, this will cause the flyweights to open up less, causing the space cam to not move forward enough, making the sensor "U" to ride up on a high side which is less fuel delivery, leaner.
But look at the "T" space cam. Not much depth differences. Lots of room for error on mid and high throttle before things go bad. Now compare the depth of the "T" and "RS". The RS has quite the deep contour and that will move the main rack much farther than the "T" and turning the plungers more to get the needed fuel delivery of the RS.


http://forums.pelicanparts.com/uploa...1253827250.jpg

Thanks 356RS for explaining this ... so is it correct to say that while the fly weight adjustments (screws #2 and #3) don't affect absolute enrichment, that they adjust relative leanness/richness in their respective RPM ranges?

Well yes, #2 & #3 will affect fuel delivery in there respective RPM/throttle range when adjusted. On the 2.4T space cam adjusting the #2 & #3 clockwise, tightening up the springs on the flyweights, yields more fuel delivery. If you try to do the same adjustment on an "E" or "S" you reach a point were the sensor starts to climb out of a low mapping area and gets less fuel delivery. Hope I explained this OK.

I have been running my 2.7 for about 1000 miles now and still tweeking it. It is good and broken in so I will be going to a local dyno to get a baseline and some fine tuning but I made a lot of adjustments up to this point and corrected some errors I made early in the process. It helps to keep a notebook on where it is set and what you adjust. I also note the weather conditions as well.

The information in this thread and this site are invaluable to a DIY guy. MFI is very good when it is finally set correctly. It also sounds fantastic especially in tunnels and overpasses at full song.

Twin plugs and compression have little to do with it as long as the timing gets set right.

A 2.7RS is 4% smaller than your 2808.

Your GE 60 cam might flow more than an S but your ports are not any bigger than a 2.7RS so air flow might not be that much different.

The easyest way to go is to call Gus, tell him what you are doing. He might suggest a starting point or sending your pump back to him so he can set it up on his bench. He needs to know your cam and exhaust as they are importang varables.

Most the time, a pump he sets up is right out of the box.

If it was a stock RS or an RS with a sport muffler as long as he know that, I would assunm his set up is right when delivered and if not right, somthing else is wrong.

If you are a DYI guy, get the car on a dyno and moniter you AFR. A MFI pump is matched to the TQ curve, not the HP curve like other injection or carb setups. It should max flow fuel at peak TQ and not give any more fuel per stroke past that. This can make for a little rich running past TQ peak if your ports are small or exhaust is restrictive and TQ is falling off. If tuned for perfict AFR at HP peak you can run a little lean at TQ peak. Thus, look at the TQ curve and the AFR delta's. If they follow each other pretty well, you can just use the simple rack adjustment to get things right. If not, the sqrings and or weights might have to be reset and Gus should set your pump up for you.

Note that different exhaust systems can cause more issue with tunning than compression, twinplugs, or the small bump is motor size you have.

Not an expert, just what I belive.

Not the cheapest, but very likely the best, can be had by PMing Burn-Bros...

Porsche 911 & Carrera Ignition - Page 8

http://forums.pelicanparts.com/uploa...1274471184.jpg

You really need a good AFR instrument to tune MFI. I have been reading all these posts and these gentlemen really know their stuff and they have forced me to think a lot about fine tuning my system.

I have driven my MFI 2.7 1973 100,000 miles, and in the last year have really gotten in running well with the help of these guys that have given you advice here, and a few others.

Knowing AFR while you are driving and actually data logging it and studying it later is the only way to go. You can do it on a dyno, and even better is to permanently install an AFR instrument in your car and look at the data after you drive it on the street or the track. I will try to post a AFR/RPM graph for you.

here is a chart. this is a 5 minute piece of a run. Seconds along the bottom, RPM on the left and in the red line, AFR scale on right. Green line is AFR.

http://forums.pelicanparts.com/uploa...1274573180.jpg