What do you mean by "progression stumble?" I have these carbs on my 2L and it pulls smoothly from low rpms on up. The only issue I have is that the car seems to buck slightly at steady speeds between 10 and 25 mph. I've always thought that had to do with the lightweight aluminum flywheel.

When I say "buck slightly" I mean that trying to maintain a slow steady speed causes the car to feel a little like it is being driven by someone learning to use a clutch for the first time.

A passenger might not notice the problem until we get into a supermarket parking lot. Then it takes some concentration to be smooth.

So ... are you talking about a cure for a stumble that occurs when you accelerate (which I don't have) or a way to fix the problem noted above?

By the by, my carbs are using 50f9's, and they were set up on a dyno, with the help of a Weber specialist who works at Pierce Manifolds.

 

I have no experience with 45's but I have two pairs of late model 40's. The correct idle jets are in the range F17 to F27. Smaller F numbers are for carbs with 2 digits after DCOE. My experience is that late model carbs with 3 digits after DCOE will not run properrly with idle jets that are intended for early carbs.
Ed Prytherch, Columbia SC
74 GTV
79 Spider
88 Milano Verde

 

Gary,
That bucking is probably caused by the progression circuit if you have the 152's. I'll bet your car would stumble at some point if you put it in neutral and revved it very slowly and progressively from idle up to say 3000 RPM.

My car has an aluminum flywheel and an aluminum pressure plate. I can now drive the car at any low speed with out the bucking, unlike before the modification.

My car also idles at 700 RPM with 2 turns on the idle mixture screws (instead of 3 1/4 before the mods) also, it idles with the throttle plates completely closed as Weber says they should be (idle speed screw 1 1/4 before mods).

I will say that a 50F9 is leaner than most can get away with. The average seems to be 55 or 60F9.

Also, I believe that all 152's are not created equal. These carbs are not made as precisely as the old Weber's. Even though these Weber's were purchased as sets or pairs, the progression holes were not in the exact same place on any of the four 152's I have machined, in fact, even from left side to right side they are slightly different (+ or - .015" in the for/aft location).

It is quite possible you have a better than average set, which might be why you can use the 50F9 idle jets. Then again I was running 60F9's with no stumble at all, at any speed, just lousy mileage and a thick sounding engine.

Ed,
The brand new 2006 45DCOE 152's come stock with 55F8 idle jets installed. I did, for fun, install a set of 55F17 idle jets to see what would happen and the car wouldnt even rev past 1500 RPM. It was completely un driveable.

Anyway, the info's there for anyone to use, though I wouldn't blame you for not, even if you do have a stumble. Even "Professional" Weber tuners shuddered when I asked for advise and told them my plan to add a hole.

All I can say is I've done it twice in the last 2 weeks and it made a big difference on my Alfa and my buddies Beemer.

I think the proof is in the pudding and, as I said, Weber now offers the 152 with the extra progression hole!

 

Hey Paul and Gary:

What are you guys doing for jetting on your 45 152s? Everyone still running the 36mm vents?

I have a set of these on my 78. Seem a little thick as Paul said. Not seeing the stumbling. I always thought the car not spooling as quick as it should. I believe around 2.5 turns on mixtures Good smooth idle once warm.

Best Regards,
John M

 

No question at all - this is the solution for the 152s. I have spent quite a bit of time staring at them but not going ahead to drill the progression hole because I wasn't sure how large to make it or exactly where to put it.

But before going ahead with this I have one question. Is placing the hole so it is in the correct relation to the throttle plate with the throttle *completely* closed really correct? How, then, does one adjust idle speed? If it were necessary to crack open the throttle plates just a bit, it would seem we would be at risk of partially uncovering the progression hole.

The only obvious answer I can come up with is that because we have the air bleed screws on the 152s we can open them to move the throttle plates toward the closed position for a given idle speed. Thus, the concept would be to use the fully closed position for the throttle plate at idle and open the air bleeds a bit if the motor needs more air. Does this jibe with your experience?

 

It is my understanding and indeed experience that DCOE idle should never be adjusted with the throttle plates, they should be set at 1/2 turn in from screw contact and not touched again, idle is then adjusted with the slow running screws, Andrew

 

Gary,
That bucking is probably caused by the progression circuit if you have the 152's. I'll bet your car would stumble at some point if you put it in neutral and revved it very slowly and progressively from idle up to say 3000 RPM.

My car has an aluminum flywheel and an aluminum pressure plate. I can now drive the car at any low speed with out the bucking, unlike before the modification.

My car also idles at 700 RPM with 2 turns on the idle mixture screws (instead of 3 1/4 before the mods) also, it idles with the throttle plates completely closed as Weber says they should be (idle speed screw 1 1/4 before mods).

I will say that a 50F9 is leaner than most can get away with. The average seems to be 55 or 60F9.

Thanks for the response, Paul. Before using the carbs, I had them checked and adjusted by Gron Perry, a Weber wizzard who works with Pierce Manifolds and does tuning on the side. The carbs came new with sticky throttle plates and another issue that escapes my memory.

I've never noticed even a hint of stumble when accelerating from any speed, it's just the steady state, low-speed bucking that is annoying. The motor revs very quickly and pulls like a train.

I've printed out your detailed instructions, but for now will probably just accept the bucking -- which is fairly minor -- as the price to pay for all the other good things the engine does.

Here are my settings, as requested by John:

Weber Settings
Chokes -- 36
Idle -- 50f9
Accel pump jet -- 40
Main -- 145
Air corrector -- 180
Emulsion -- f16

And, for those who find this thread before reading about the wonderful Dave Andrews carb setup software elsewhere on the BB, here's where to find it:
http://gwandrw.com/Alfa_105_Technical_Info.htm

 

John,
34 choke
4.5 aux ventury (stock)
140 main (needs to be 135)
190 air corrector
F9 emulsion
55f8 idle (stock)
35 pump jet
40 pump bleed (stock)
200 needle valve (stock)
floats@12.5mm

ildino,
Yes, bleed screws, yes

 

Gary,

What kind of cams do you have and whats your timing curve like?

 

Jon Norman Megacycle 11mm cams, with Centerline ID405 electronic ignition. I don't know what Centerline dials in, just that they say the advance curve is "more aggressive."
My timing is set at approximately 34 degrees maximum advance.

It's probably important to note that my big-valve, mildly ported cylinder head was built specifically for the DCOE 45s by Rich Goodrich, who also port matched the intake manifold. For those who don't know who Rich is, some of the better West Coast Alfa wizards credit him as a mentor.

 

Thanks for the jetting guys. I am running stock 152 components except for the air corrector. So 36 vents, 145 mains, so forth and so on...but anywhere from a 190-210 air corrector. I believe I have 200s in there now. I may have changed something else minor....but I'll have to go back and open it up to see. Heck...I may have changed the mains to 140s....can't remember for sure.

Ignition...believe it or not....I am running 40 degrees advance all in around 3500 rpm. RML distributor, MSD 6AL multispark, 10.4 pistons, decked head, 11mm cams, oversized valves. Running this to race ole Budsy....but will back down to Gary's neighborhood for regular driving.

Didn't notice any detonation. But I am faily certain that I am running too rich. So probably will start tinkering soon again on the jetting. Also not so happy with the power curve placement being so high with the 36s. Might go as Paul did with the 34s and just start over.

Paul, excellent writeup and info. I'll be sure to utilize your information that you so kindly shared with us all. Much appreciated!

Best Regards,
John M

 

And He Still Couldn't Beat Me!

 

I just pulled the plug above the progression hole on my carbs. With a flashlight, you can see (through the holes) the throttle valve move and approximate it's position. On my relatively new Spanish 45DCOE152 carbs, there are 3 holes per throttle, as Paul describes. And just as he describes, the throttle plate is NOT properly positioned immediately below the hole closest to the engine. As I push the throttle I can see the plate appear at the first hole and then move past it giving clear evidence the throttle plate is not in the proper location.
Very interesting, as this would explain why my carb was jetted professionally with a 60F9 idle jet and gets horrible gas mileage. I also dyno tested and the exhaust gas was very rich at small throttle openings. See here.
So, I just ordered a bunch of jets and am going to put a smaller set of idle jets in and see what happens, but I expect the car will start to buck off idle with the smaller jet. I have a friend whose car bucks exactly this just off idle when cold. It is perfectly explained by the fact that the engine would get no additional fuel until the valve passes that first progression hole! But I'll test it out before doing the machining just to complete my "due diligence".

To anyone else considering a problem with hesitation or bucking off idle or a car that runs fine but gets surprisingly bad gas mileage, this deserves investigation. Inspecting the progression holes is VERY easy, can be done with a screwdriver and a flashlight. I'm attaching a picture below showing right where they are. Be sure to clean the area carefully first, as you don't want to get any dirt at all in these progression holes! And don't over tighten the brass plug when you reinstall it.
If your car is hesitating or bucking, it is also very easy to change the idle jets, they are right under the thumbscrew hats on top of the carbs. Putting a richer jet in should solve that problem, at the expense of your gas mileage.

My sincere thanks to Paul for writing this all up so nicely, and for corresponding with my directly with some very useful tips!
Carl

 

Progress? Well, I pulled my 60F9 idle jets and swapped in a set of 50F9 jets. (I have a set of 55F9, but decided to go significantly leaner to see if I could see a real difference. After warming up the engine, I carefully set the idle mixture screw. Test drive: seemed to run fine! I think it sounds and feels better with small throttle openings now. Then I brought it back to the garage for some more testing.
The book says you can test the progression mixture by slowing opening the throttle with the idle speed screw. If the engine runs worse around 1300 rpm, you can test the mixture with the idle mixture screw. (note the difference between the idle mixture screw and the idle speed screw!) I couldn't get much to happen with the idle speed screw as it was tough to turn in smoothly, but with the throttle pedal I could get the engine to significantly slow down as I just feathered it in. A bit more throttle and everything would be OK. I didn't notice this driving, it really is a just feathering the throttle thing. Hmm. So I opened the idle mixture screws a half turn (this slowed the idle as it made the mixture too rich) and tried the pedal again... and the problem went away. This means richening the mixture helped the progression circuit run better. Next step would be to mark the throttle position where the dip in engine speed happens and to see if this corresponds to the area of the progressions holes. I'm betting it would.
I reset the idle mixture to where it runs best at idle.
Now I have to think about this. Everything is a compromise. The car seems to to drive OK, at least in this warm weather. But I wouldn't be surprised if it started to stumble off idle on a cold morning! I'd love to put an exhaust gas analyzer on it and see what happens as I slowly open the throttle!
I could try just opening the idle mixture screw a bit like during the test. That would result in a somewhat rich idle, but did seem to remove the stumble.
For the moment I'm going to leave it with the leaner 50F9 jet and drive it a bit...
C

 

Couldn't resist... I went back to the garage and marked the throttle position and slowly opened the throttle. It does appear the that the stumble, or dip in RPMs does happen right around when the throttle plate passes over the progression holes (with the 50F9 jet). I'm darn tempted to have these extra progression holes put in...
C

 

I remember I had similar issues running 45mm dellortos. I was able to open one of the progression hole a little rather than drill another hole. Also spent ages experimenting with the airbleed holes on the idle jets using tip drills and solder. Once I got them right I bought a set of jets drilled them and left them alone. The motor ticked over at about 700 rpm and behaved pretty well in the progression phase given that it was heavily modified with some crazy duration cams.

 

Apologies for digging up old threads.... I have a weber 45DCOE 152 which has a higher air flow in the 4th cylinder.

Pls see the youtube clip.

The question is whether I can use the 152's Air Bypass bleed screw to equalize the air flow?

 

Impressive guys! I've been restoring Weber units since the '60's and have seen few discussions as on point as this one. I avoid the Spanish Webers largely because of what has been discussed here, lack of flexibility for many Alfa applications without additional labor. Gron Perry will agree with this! Even the late Italian 138 /139 series are more tune - able, without additional progression holes or modified (grooved) throttle plates. The problem for the Weber restoration fellow like me, is cost that needs to be passed on to the customer. When I have to R&R throttle plates, mill a groove in them, or drill precise additional progression holes, that takes time, and costs money. My customers are better off with a set of 40DCOE2's or 45DCOE9's to begin with, even though more "used". Your discussion IS right on the money, and I am pleased you all have spent the time to discuss this problem. As mentioned, some of the newest "stuff" from WEBCON addresses these issues, and will hopefully return us the Webers we want that are flexible in application.

 

 

ok...wonder if Max has the same problems on his modified t/s he runs spanish made too

 

drilling guide

Has someone used this drilling guide?

Weber DCOE Progressive Hole Drilling Guide - Webstore item#21166704

 

I hand made one like it with three holes from a ruined 40DCOE2 body that had good progression holes. I then used this jig to modify some 40 and 45 DCOE's. Sometimes it worked well, other times not so well. With the cost of vintage Webers what it is, I no longer modify the progression holes. If changing sizes and notching plates (if required) won't do it, I find a better Weber for the application.

 

Used: Old stuff that nobody wants. It gets FUBARed so bad that its junk.

Vintage: What's left after all the old stuff has been FUBARed. Ten times the price now.



Robert

 

I had this modification done by John over at Costa Mesa R&D.

I think it modification got rid of this stumble in the progression circuit.....BUT now the carburetors have a strange squeek, yes squeek that they make. I am not sure what is causing it but as the car sits there idling, each of the carburetor tracts constantly squeek as the engine draws its intake pulse. squeek squeek squeek squeek ever engine cycle!

Can anyone tell me what the hell is going on?

Also my synch is off within the same carburetor, meaning that when I put my synchrometer on the two different horns of the same carburetor, one flows slightly more than the other. I made sure the bypass screws are closed and everything was snug.

I did discover a small leak around the rubber isolator of the intake tract which flows higher, I am going to fox this air leak this weekend but I suspect the problems are not related. I hope this is not a workmanship issue, perhaps the hole on this tract was drilled incorrectly compared to the other ones?

Any input would be appreciated.

 

The squeak sounds like an air leak at the gasket between the rubber mount & the carb. I use 'Wellseal' with the gasket (it's not affected by petrol, unlike some sealants)
Difference in flow between barrels of the same carb sounds like a twisted butterfly shaft to me.

 

The butterfly plates could also be slightly out of adjustment. You need to remove the carb to fix. Inspect by looking at the engine side of the carb with a bright light on the other side - both butterfly plates should be fully seated with NO light showing. Often one plate is slightly out of place and some light shows thru.

With the intake side facing down, slightly loosen the two screws in each plate. Wiggle the throttle shaft a bit - you should see one of the plates shift a bit and seal all the way around.

Robert

 

Before taking out my carbs I took a few pictures of my modified progression holes. These were done by John at Costa Mesa R&D.

Front carb:

Rear carb

Seems to me that holes are located differently on one carb compared to another.