Installed my 40 DCOE webers on the L24:

Engine specifications

2.4 liters original motor/head/cam.

Pertronix ignition

Pertronix 1.5 Ohm coil

MSA 6-2-1 headers

adjusted idle mixture screws 1/2 turn out

Adjusted all idle speed screws (without actuator rods hooked up) until they were about to uncover the first progression hole

I had at my disposal, an wideband O2 gage installed into my header (innovative LM1)

and a Air Sychronizer tool with weber air horn adapter

(note, air horn adapter not shown)

My factory out of the box settings for my 40 DCOE 151's were:

30mm venturi

130 main Fuel Jet

170 Air corrector

F11 Emulsion tube

55F9 idle/slow running mixture jet

Car would not start at all. It would run off of the gas put out by the accelerator pump, but would not stay running. I kept increasing the air fuel mixture (note NOT touching the idle speed screw at all) until the car would start and stay running. This ended up at 2.0 turns out from fully closed.

At this point, you MUST let the car warm up to operating temp. After the car warmed up, I was getting an AFR of 10.1 on the LM1. Too Rich. Mr. Franck's of side draft central's white paper points out we should always aspire to 12.5 with our DCOE's. Well I managed to get it to be there running about 1.5 turns out from full close don the air fuel mixture. Car ran smoother like this as well.

Initial drive was very promising. However, the dreaded flat spot did exist in the transition point between my third progression hole and when the main circuit came in.

I dove back into the side draft central white paper, and a way of getting the main circuit to come in faster is to reduce the size of the air corrector. You see the air corrector is like a vacuum bleed off. In order for the main circuit to work, you have to get the column of liquid up the emulsion tube and down to the venturi. This is done by way of sensed vacuum from the engine. See 3rd picture on the left.

The larger the air corrector the more engine vacuum is bled away and it takes more vacuum to pull the fluid up the emulsion tube chamber. Capillary action only gets you so far, and often the stumbling effect is the engine vacuum is too low to effectively make the transition from progression circuit to main. This should happen at about 1400 rpm according to Mr. Franck.

Upon driving around I noticed that my part throttle, 4th gear, low rpm (2000 rpm) steady state cruise I was reading about 15.9:1. This is too lean, BUT I knew that running 130 main jets which are really a bit large for 400 cc of displacement I did not need to richen up the main jet. So instead I put in 160 Air Correctors,down from 170. I touched nothing else, and went for a drive. My flat spot on transition was greatly reduced and even eliminated in 1st gear. But was still present on all other gears. However the lean stumble was smaller and the main recovered quickly.

I bet your wondering, Hey Zedyone, what about your floats? Well I am not going to change anything else until I check those.

Let me make one thing clear, you should always check your floats BEFORE you do any tuning. The float level can drastically effect how and when your main circuit comes in, as a low float level will increase the distance the fuel has to travel up the emulsion tubes.

I purchased the Keith Franck float measurement tool off side draft central webshop. I will be trying to see where I am this week. It would be foolish to spend any more money until I check the float levels.

Also, not mentioned here, but I did check the air flow through the carbs for balance with my sync tool pictured above. Right off the bat with the engine warm, they were within 0.5 of each other on the tool. So I left them alone. If I wanted to change that, the only way to make fine tuning adjustments between the carbs is to adjust each idle speed screw located on the side of each carb. I did check balance on both barrels of each weber individually and the flow was identical on all three carbs. Weber does include a way to balance each barrel of one carb individually, but I figure that adjustment is probably to make up for some external imbalance, be it rings, seals, etc. If the butterflies on one carb are open the same, then the air flow should be the same. If they are different, there is an external reason. New webers the air flow should be identical.

When I check my floats, I will post pics and report back.

The plots are from a nice guy on the yahoo side draft forum.

I have a theory about the rich spot at ~2,200 rpm too. It is because the top of the throttle plate pinches off with a thick choke next to the accel. nozzle promoting more flow. The accel pump will always open and push as the throttle is pressed and vacuum at this pinched spot will pull more fuel for a moment of transitition.

I was banned from HybridZ so I will never join...even if I wasn't banned... some useful info there but the admin are "weenies"

I am sniffing at the tail pipe like you. The copper pipe I made is 600mm long to get a better sniff at idle as it goes deep into the exhaust system.

snip I always setup idle at best lean condition then play with idle screw to set the idle speed correctly.

snip

THANKS! I have been thinking more about your words and it suddenly occurred to me that the idle and the progression do interact however tuning at idle seems illogical as the car must be tuned to run, not to idle AND because the idle enrichment screw can fudge things.

I think tuning by addressing the progression and cruise first is the best way to start. Fudging air/fuel mix with the enrichment screw at idle and throttle plate is sort of backwards because at cruise, the idle jet should not be significantly feeding the motor. In theory at cruise, the jet and the progression holes AND the throttle plate are the only significant components and the throttle plate will fall where it naturally does to provide x amount of air at cruise.... so by cruising, one can alter the jets to get the right a/f mix then go after the idle.

In fact it would be interesting to try to tune with the enrichment screws closed completely and just use the throttle plate opening to pull from the first prog hole. If the car will idle like this then a quick cruise with A/F monitoring will tell whether the idle jet is too rich or lean.

Edited July 29, 201410 yr by Blue

just to make sure, when I was referring to "idle screw", I was talking about the screws used to balance the carbs & RPM at idle, not the ones used to play with AFR.

Yes I understand. In fact just last night I read a section from "How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors" (SpeedPro Series) by Des Hammill. The section on choosing and tuning idle jets is exactly what I concluded above... convergence is a good thing. Basically he says to choose jets for cruise at progression and for power transitions through progression then address the idle.

I'll post some of my internet vacuuming finds in a new post.

Edited July 29, 201410 yr by Blue

Today I changed out my 30mm chokes for 32mm chokes. As you would expect not much has changed as far as idle quality, but having said that. For the first time, I was able to get the carbs perfectly balanced at 1000 rpm dead on. All 6 cylinders were pulling identical amounts of air, and also, my AFR was as close to steady as it has ever been. I could get a decent idle before, but it would fluctuate from 12.3 to 13.4, and would cycle seemingly randomly around there, but average about 12.7. Now I do not vary more than .4 on my AFR. I stay about 12.9 to 13.4. My part throttle seems smoother, and it picks up revs very quickly. I cannot wait to drive it to see how she feels.

But for now, I have the car on jack stands with the front spook off, I am waiting for my ducted spook..

try 20 degree initial timing and see if you idle smooths out you may have to retard more at heavy load/wot but it made a big difference for my tuning yesterday

negative. If run more than 13 I get some pinging at heavy load in 3rd and 4th gear. With 10.5:1 compression that was going to be a risk I was taking. AT 10 degrees advance, I get none. Car seems to run fine. I will try to bump up the octane and run about 14-17 to see how she likes it. I know webers like lots of initial advance. If I can ever get my mallory unilte to work without blowing the ignition module I will order the curve kit for it so I can run more advance initially.

To tune timing at idle, I start the engine (while already hot) with distributor loose so I can turn it by hand. Turn it and hear the difference from the engine, the rpm will increase or decrease. Best timing will be when the idle will be the highest. This is where you should setup your timing.

Check with a light where you stand and record the value.

Do a quick math to determine your dizzy advance based on targeted total advance wanted. With a Mallory Unilite, you can set up this advance. You don't need specific tools (even if it would be nice to get). To offset properly the dizzy, I measure the arc length vs. the radius from where I do the measurement. then I use drill bits with corrrect diameter as a gage for proper adjustment of the 2 plates inside.

That's a good idea

Never even thought about modifying it myself. That definitely easy to do

Well I took the Z out for a drive with its new 32mm chokes. I made all the appropriate jet changes to come to this configuration:

130 main Up from 120 main

180 air corr Up from 170 Air corr

55F9 idle Up from 50F9

My first impression was that there was no change. It still idled as smooth as it ever had (no small part to finally getting the air flow through them perfectly balanced). With the 55F9 idle jets, I get 13.9 to 14.7 AFR on steady state cruise at about 60 mph. Even better when I tip into the throttle the AFR drops to only about 12.8 or so. Very nice. At wide open throttle the power improvement is not trivial. It just seems to have more legs up top. It pulls with more authority.

So all would seem to be well. But is it? The answer is mostly, yes, and a little no. As one might have expect the throttle response is NOT nearly as sharp as with the 30mm chokes. 32mm is definitely on the ragged edge of what I would want to have in a street car. Not that it feels sluggish, or laggy. It does not. It response to all the inputs I give it in the gas pedal. But not nearly as sharply as before.

The engine with the 30mm chokes seemed to want more air all the time. So any opening of the throttle plate made the engine just respond like getting a breath of fresh air after surfacing from the water after a long dive.

The engine seems more relaxed with the 32mm, it idles better (not sure chokes should make a hill of beans at idle though), and the ferocity of the upper rpm is notable.

So long story, for a street car 30mm chokes will work fine on a L28, and give you immediate throttle response that makes a car VERY fun to drive on the back roads. But for a car with deeper lungs, the 32mm are the ticket. If you track your car and live in the higher rpm, I can completely recommend 32mm chokes maybe even bigger.

My cliff notes is that going to 32mm chokes is not a holy grail of modifications to webers. There is a downside. The magnitude of that down side depends on your personal preference and what you value.

Great report! What was your AFR at 4k and at 6k?

Last weekend when I measured and recorded A/F as my brother drove, his driving commentary matched the A/F ratios I recorded: Going with bigger idle jets and lower AFR made the car "sluggish"...similar to your commentary above wrt 32 vs 30mm.

I am wondering if you can play with mains and air with 32mm chokes to see what happens on each side of 13AFR between 4k and 6k. (120f & 180a vs 130f and 170a)

OH blue, thanks for reminding me.

I meant to include that the 180 Air Corrector reintroduced the slight lag in between the progression circuit and the primary circuit. This happened with the 30mm chokes as well. When I went down to the 170 Air corrector with the 30mm chokes it was gone. I tried the 180 Air corrector on my L24 as well before the engine swap and I had a noticeable flat spot between the two circuits. The 170 air corrector fixed that there too.

I wanted to give them a try again with the bigger chokes, but the transition stumble was back. I have installed the 170 air corrector again, and I will see what the AFR is at 4 and 6. I have hard time getting 6k rpm 3rd gear runs,as that is really darn fast on public roads! But I will see what I can get you Blue.

Hopefully those 120 mains will be on your doorstep this week or early next week . I kind of wish I had 125 mains. I feel another order of jets coming on.