LM-1 results from race motor

[speedo]

I built a 2.2 motor from scratch...10.5-1 cosworth pistons, Elgin cams (similar to GE 80s), non CB 2.2 crank, S rods, single plug.

My 40 IDAs are set up as follows at 8100 ft:

Venturies 32
mains 120
idle 60
air correction 150
emulsion F26

I hooked my LM-1 up to the headers and powered it off my fuse panel.

Then I went out and recorded three loaded runs and averaged the results:

RPM AFR
1000 15.8
2000 11.5
3000 11.8
4000 12.0
5000 12.8
6000 12.9

So basically what this tells me is that I am lean at idle, and the slightly too rich up the rpm range. The motor will pull to 8000, but I am in a mountain neighborhood and it isn't cool with the neighbors to be too noisy...so I didn't get the 7000-8000 AFRs.

I am to understand the rule of thumb is if you are lean in mid range(3000-4000), then you increase the main, conversely if lean high(6000) you lower the air correction. If you are rich mid range you decrease the main , and if rich high range you increase the air correction.
Since I am slightly rich mid and high...this means I need to decrease the main and increase the air correction .

Something here seems backwards...I can't believe that I am supposed to go down on the mains. 120s are already pretty small. I was going to bump the venturies up to 34s and was prepared to go to at least 130. But I wanted to check the existing specs before doing so.

Anybody want to weigh in on this?

[speedo]

C'mon guys...no responses? I thought there were still some weber wizards out there! Everybody convert to CIS and DME?

I guess I will just have to experiment on my own. Tomorrow night the 32s get swapped for 34s, and the 120 mains for 130s and the idles come back to 55s. Next step will be to push the air correction jets to 180s. I will run the numbers on the LM-1 and see what I get.

[JohnJL]

Actually you are probably pretty close to done there. Max torque I think is around 12.8:1. Maybe try going up a half size on the air correctors.

[Eagledriver]

I'm not an expert on how well you can get carbs dialed in but those numbers look very good to me. I would want to get a look at the top end though to make sure you don't go too lean. A lean idle is good, it keeps you from fouling the plugs.

-Andy

[911quest]

How is your timing set up your numbers are pretty good actually newer fuel injected cars strive for about 12.5 to1. But you are dealing with turn of the century technology here and is a compromise at best.

[Steve W]

Your upper rpms are good. If you can lean out the midrange from 1000-3500 rpm, to around 13.5 you will gain more torque.

[cgarr]

Originally Posted by Steve W

Your upper rpms are good. If you can lean out the midrange from 1000-3500 rpm, to around 13.5 you will gain more torque.

How is this done without changing the upper end? Different emulsion tubes?

[len911]

Speedo, just out of curiosity... Did you use the LM-1 with the RPM converter cable or does the plain LM-1 have the capability to log that? Thanks! Lou

[cnavarro]

Having done this exercise in my 912 with my toned down race engine with the aux box and inductive pickup for RPMs, I'd personally be happy with what you've done. If you're concerned about the idle being a little lean, just put in one size larger of an idle jet.

Playing with emulsion tubes can get expensive very fast. I tried so hard to get my engine dialed in with the LM-1 and carbs so tightly, that I probably spent hundreds and hundreds in useless e-tubes and other stuff.

What were the AFRs spiking at off throttle, when shifting, then hammering back down on the throttle, just out of curiosity?

[speedo]

Thanks guys...

I was at the RMVR enduro this weekend. The result of test and tune ended up with me bumping the mains to 140s and going rich at 7200 rpm to 13.5 which looked good. I had a few other problems....oil leaks...and air mixture screws backing out. The jump to 140s gave me a flat spot at 4000 to watch out for. I need to bump the venturies up to 34s to see how the system responds. Thanks for the input.

Speedo

[cgarr]

Originally Posted by cnavarro

What were the AFRs spiking at off throttle, when shifting, then hammering back down on the throttle, just out of curiosity?

I have been checking AFRs on my 912 What I ended up with was. Idle is dialed in at 14.5 I ran a 2nd gear from 2000rpm, starts at 11.2 and climbs slowly as RPM increases to about 14.5 at 6000 then spikes to 21 or 22 when shifting then back to 11. I guess these engines are just big air pumps when you let off on them. What I have in it now is:

86mm J&E 9.5/1 Pistons
Weber 40 carbs with 34mm chokes and 4.5 secondaries
Idle 67
Mains 135
Air correction 190
E Tubes F7 or F11 really didn't see any difference.

I was hoping to get it leaner thru low and mid range and richen up slightly at high rpm but have not been able get it there. What are you running in your 912?

[cnavarro]

It sounds like you might have either an exhaust leak or intake leak throwing off your numbers. My 1883cc 912 ran very rich at idle with 55 idle jets! I'd check there first. That was my problem when I was trying to tune - the manifold had actually cracked.