Using this cheap LCR
https://www.amazon.com/gp/product/B07CYSV5L...e=UTF8&th=1

I have been tuning my MPS. Finally got it, had some real issues getting it rich in the right spots for my 2056 build. I doubt I had it 'right' for my worn out old rings and guides. Anyway. For the past couple weeks I have been poking at it. Taking measurements, graphing the results of little tweaks.

Today I got it pretty darn close. The top line in the graph is the one I am running currently. It was not easy to get it there. Each adjustment affects the others. It is still a little rich at the top and a little rich at the bottom, but cruise is where I was having the issues. Just took a long interstate drive and it no longer goes lean anywhere.



The first graph shows the range from leanest most linear to the final. You can see how much the lines slope can be played with. Not much.

Click to view attachment

I didn't take full measurements on the initial but it wasn't good. To get it to run without going super lean at cruise I had to put a 50 ohm resistor (in addition to the 73 270ohm CHT resistor) on it.

Suprising to me is how little change was required to make that spot 'prefect'. Also, the affect on WOT (low inhg) was small. A little richer than before but not much. Anyway, here are the data points for those of you that may need to go here someday with a cheap LCR. I am at 850 feet above sea level, but I don't think trying to get the actual values is worth much. I think it is more about the slope.

Click to view attachment

What are you measuring? Is it manifold pressure sensor impedance vs. actual manifold pressure in inches of mercury? Your cheap LCR (inductance, capacitance, & resistance aka reactance & resistance) meter is probably adequate for the job. Please explain. Nice plots BTW, but you need to better label the axes.

Sorry, inductance on the y axis, inches of mercury on the x. The mps is out of the car on a mightyvac. LCR is on ports 8 and 10 on the mps.

Those y axis values are no where close to the Anders values. Wonder why the discrepancy?

Yeah, no kidding. I guess it's probably the cheap Lcr? Pbanders mentions the importance of using the same unit as he used.

My min value is .43 and max value is .90. I can't make the mps do more or less. I believe Anders range was .5ish to 1.5ish. so very different.

It would be awesome if you could add a plot for AFR using the same x axis.

I can! I just need some time. Tomorrow I am going to try and make some videos and pull the vacuum and AFR off that.

I have a Wavetech LCR55, which is what Anders used.

I built a 2056 with a Raby 9550 Cam and LN 44 x 38 heads, 123 dizzy set to 30 degrees BTDC.

I installed a O2 sensor on a heat exchanger so that I could better adjust the MPS.

I set the MPS for the following AFR:

Idle: 14.5
Partial load: 13.5
Full load: 12.5

This resulted in the following LCR readings:
0 in Hg: 150
4 in Hg: 128
15 in Hg: 80

The car performs better than I could have expected.

I also created a web page to help tweak Ander's numbers based upon altitude. If your computing device has GPS capability it automatically determined the altitude. If not, you can enter it manually.

https://mps.dolimpios.com/

I hope you find this helpful!

Art

Interesting! How did you take rpm into account when you were shooting for part and full load? Just curious. Thinking about how I am going to handle that tomorrow....

Honestly I was driving it and guessed at the position of the MPS.

Cruising at 55 and then releasing the throttle should produce maximum vacuum and pull the slug against inner stop. The inner screw is used to adjust for this.

Cruising at 55 and just maintaining speed on a flat road would be somewhere in between. The outer screw is used to adjust for this.

Wide open throttle at about 55 would produce 0 in Hg causing slug to rest against outer stop. The plug that screws in to close the access hole is used to adjust for this.

It was pretty time consuming to get it right, and it must do it in the order above, inner screw, outer screw, plug screw.

I did that the first time I tuned my stock engines rebuilt mps. Not easy, and when I got around to doing it with my 2056 it really wasn't working. That's when I just pulled it and set it by the slope. I just couldn't get that part load right. I consider part load 12-8 inhg, as that is the hardest part to get right. After 8 you get that full load ramp up as the diaphragm pulls free of the part load stop. That's why I put in a vacuum gauge. I had to know where exactly my problem was. Flat ground cruising at 70 I am sitting at 13-14ish inhg. Slight dip in the throttle and I am at 10inhg. I was getting crazy lean numbers there that I just couldn't tune out with the outer screw. With a fancy cam, those numbers on vacuum are probably all different.

i dont have an LCR but just used my AFR when adjusting the MPS for my 2056 and my readings are almost identical to yours, except im a bit more rich at idle, , i am happy with ther performance and temps, i didnt have to make much of a change vs my stock motor, except i did add that in line pot resistor a 0-500ohm one and its pretty much at about 350-400 which helps keep my hot start idle from being too low, which is known issue for these cars, i believe starting back up being too lean? anway with that its not an issue now, - i would love to play around with an inductance meter can you share your link for the purchase?

Phil

Here is that LCR unit. 32 dollars I think https://www.amazon.com/gp/product/B07CYSV5L...e=UTF8&th=1

Just did some videos of my afr at various loads while driving around (highway, interstate, town). Averaged readings across time. Whenever I could catch a nice steady state at a particular vacuum level while watching the video replay, I would jot down the afr reading. I then averaged those afr readings together. I did bump up my timing to 29 today as well.

0-7 inches = 11-12:1 highly dependent on engine RPM. WOT Lugging it stays low, high rpm it starts to climb sometimes, not always. Still making observations on WOT.

8-11 inches = 13:1 pretty consistently

12-13 inches = 13:1 pretty consistently, this is pretty much where it sits cruising with slight hills at both 60 (2800 rpm) and 72ish (3200 rpm).
14-15 inches = 14-15:1 This is that light cruise area where you are just feathering the throttle. My worn out old throttle body hates this particular spot. I also suspect right around 15 is where the advance is kicking in or kicking out.
16-19 inches = 15:1 but dropping rapidly as it climbs to 19 inches. I suspect this is because the throttle is just so closed at this point that it is just air starvation richness. 
20 inches = idle 13:1 (I have my ecu very lean to achieve this, almost max lean)
21-23 overun = rich in some cases, 16-17:1 in others. I don't really trust the over run readings. My decel valve works pretty good so I don't go any higher than 23.

my o2 sensor is at the junction of cylinders 3/4 in my ansa system before it goes into the passenger side muffler.

Click to view attachment

It's all about the AFR and it seems like you have it dialed-in pretty well. It's interesting that my ECU is set pretty rich. The only issue I have is that my cold idle is low. I was thinking about installing a second Aux Air Valve in parallel with the existing one to give it more air while cold.

They no longer make the Wavetek, I found mine on eBay for $40 and it was never used - still in blister pack. If the AFR is good, I don't know that I would worry about the LCR readings. I recorded mine just because it's interesting and thought that it might be useful for others with a 2056 that don't have a AFR gauge.

This is my 3rd 914 and it runs so much better than either of the other two, it's amazing.

Yeah, I don't put much into the inductance but I do think getting that curve (slope)right is important.

I opened up my full load stop today too (just to the point where at 0 inches the diaphragm is resting solidly on the full load stop. I figured it was already rich on WOT most of the time but occasionally I would see it go lean on a long pull. That's fine now. I might put a nother degree in timing as well. I did some experimenting and found the 123 appears to be 1 for 1. Put two in at idle, get two at 3500. Makes life easier. I still double check but it is so much easier holding the gun and turning the distributor without have to try and hold the engine at 3500 at the same time.

Also, I just realized you can set the Lcr to 3 significant digits and that actually helps. Pbanders had it set to 20 but I knocked it another higher and it really lets you finely adjust those screws.