engine and drivetrain Dcoe Tuning On New Engine -

[FB73tii]

There is a "Weber Tuning Manual" that has detailed jetting and emulsion tube info. The emulsion tube info begins on page 25.

 

Direct link to PDF

http://www.lainefamily.com/images/WeberTuningManual.pdf

 

Credit to Geeom for posting it here:
Original Weber Tuning Manual.pdf
http://www.bmw2002faq.com/topic/136821-original-weber-tuning-manualpdf/

 

Best of luck with those DCOE's! --Fred

[TobyB]

Quick and easy test once that regulator shows up-

put an electrical pump on it.

 

You can temp it in just for testing, and see if it helps.

 

The pulsation shouldn't be much- I wonder if that pump's overperforming.

 

t

[zinz]

just because it says "40DCOE" on both carbs, does NOT mean they are the same.

 

 

I wouldn't know anything about that...

 

My Solex bodies are very clearly marked 40DDHT. 

 

Lars saw pictures of my carbs and pointed out they were not DDHTs, but DDHs because mine have the starter device on the top and the DDHTs have the starter device on the side of the body. In my case, it really didn't make much difference, the point is you can't assume ANYTHING with used carbs. ( we never could figure out why my carbs were marked like that)

 

I am one of the fortunate few in that my carbs were unmolested and after simple rebuilding and some basic jet changes, they run great.

 

Ed Z

[felix_666]

UPDATE

 

What is the correct fuel level in the float? See here for the technique and here for the measurement.

 

On this site I have found both 25mm and 29mm being circulated? I can't find a value for this measurement in any of the 4 manuals I have for Webers.

 

The reason I ask:

After checking over things and measuring the jets etc I started the car and it ran ran worse than ever. I took me a little to remember what I changed, the FLOAT LEVEL.

 

The float shut off height was originally less than the 8.5mm that I adjusted the floats to currently.

 

In other words, the car ran better beforehand when the the shut off height was less, perhaps around 7-8mm.

 

I now understand the importance of the float level, but would like to calibrate the floats using the wet method. 

 

EDIT: I found this on the interwebs which concurs with the earlier link I posted.

 

Edited September 15, 2014 by felix_666

[FB73tii]

Ha! very cool, though the store linked on the page you found this does not list the tool. I have thought of using a capillary tube, or perhaps just an empty clear ball point pen insert to measure fuel level. Here's a couple other ideas:

 

Keith Franck Weber float measuring device
http://www.classiczcars.com/forums/carburetors-s30/45968-tuning-40-dcoe-weber-151-l24.html

Instead of using a caliper, you can use a piece of printer paper rolled up. Measure 25.5 mm and 24.5 mm on two separate lengths of rolled up pieces of paper. Poke the 25.5mm roll in the e-tube well, it should come up wet. Then take the 24.5mm roll and put it in...if it comes up dry, then you are good to go.

http://www.zcar.com/forum/10-70-83-tech-discussion-forum/326657-weber-dcoe-stumble-question-2.html

 

[felix_666]

Thanks for the suggestions Fred, but the measuring process isn't my issue, the correct value (distance), 25mm vs. 29mm, is my question. 

 

From the following post I'm guessing there is a range between 25-29mm at which people set them to, however, a 4mm tolerance seems rather large given that the static calibration of the floats has a tolerance of 0.5mm.

 

It seems 25mm is the preferred measurement, I'll have a crack at that. 

 

Cheers.

 

 

25 mm max 29mm standard 25mm is good when you are lean just off idle
or lean main jet tip in. I use a old pen and an old pen cap set it to 25mm or what ever you are testing and I look through the tube and can see when its right for the setting you are trying to get. For were you have them
set it will most likely be at 29.5mm. I have used a sliding caliper too.

 

Edited September 15, 2014 by felix_666

[chrisrouse]

Not to beat a dead horse here, but are you SURE your ignition system is TOTALLY PERFECT? I was chasing some running problem around on a Tii the other week- CO and HC levels all over the place and car falling flat on its face when I put the pedal down. The ignition wires were new, but the ends were not properly seated on the coil wire (as in the connections to the copper core of the wire). Fixed that and fixed my problem.

 

That said, I've seen throttle plate/progression hole relationships that looked just like that, and it was due to imprecise progression hole drilling and NOT bent throttle shafts.

 

I've also seen cold start pistons not seating properly due to corrosion in the bore/on the piston.

 

I've also seen floats that don't float, causing the needle valve to never shut.

 

I've also seen people set plastic floats to brass float specs, causing the level to be wrong.

 

http://www.piercemanifolds.com/category_s/317.htm

 

Also, 50f8 sounds a little lean for your set up. I'm running 60f8 idle jets in my typ151 40mm DCOE's on a 10:1 motor with IE 292 cam.

 

And lastly, you should be dead nutz as far as barrel to barrel flow for proper running. It's easier on the later DCOEs with the air bleed screws, but poor carb synchronization will cause surging, poor/rough running, low power, etc.

 

7-8 at idle on an ste syncrometer is WAY to much sucking at idle. Mine motor pulls like 3-4.5 per barrel at idle. make sure that your idle screw is backed way off (slow and "tractor-like", barely idling at all) for idle mixture tuning. If the throttle plate is too far open (read, open at all) you're running on the progression circuit and your mixture adjustments will be for shite.

Edited September 16, 2014 by chrisrouse

[felix_666]

Not to beat a dead horse here, but are you SURE your ignition system is TOTALLY PERFECT?

No, as mentioned previously, I can't get to 3000+RPM to dial all in timing. I am thinking of increasing the advance a little after ruling out a couple of other things first.

 

That said, I've seen throttle plate/progression hole relationships that looked just like that, and it was due to imprecise progression hole drilling and NOT bent throttle shafts.

Plates have been fixed, there are no holes in the throttle plates.

 

I've also seen cold start pistons not seating properly due to corrosion in the bore/on the piston.

Clean as a whistle.

 

I've also seen floats that don't float, causing the needle valve to never shut.

Floats are my predicted issue, I think the level isn't right, combined with slightly high fuel pressure = too much fuel.

 

 

Also, 50f8 sounds a little lean for your set up.

?? No 50F8's here. I'm using 55F9. Did you see the pic of the plugs?

 

7-8 at idle on an ste syncrometer is WAY to much sucking at idle.

I don't think you can compare numbers, I thought. From my understanding, its relative to the carbs you're syncing. If they both say 7, then they are both pulling the same amount of air and therefore "synced", right?

 

What does your car idle at, this obviously makes a difference?

 

When I pop the progression covers off, at idle, the throttle plates can just been seen in through the first progression hole. Over the weekend I was driving an Alpha 1600 Junior with has DCOE's and runs pretty damn well, I had a look at where the throttle plates were through the progression holes at idle and they were pretty similar to mine. From what I've read the throttle plates should be right on the first progression hole at idle, ready to open up as soon as you put your foot on the throttle.

 

Thanks for your input.

 

I think it will be a combination of rich idle jets, too much fuel pressure, slightly incorrect float height and perhaps not enough timing advance.

 

Got some free time this Friday to stick the regulator in, hopefully I can report back with something new.

Edited September 17, 2014 by felix_666

[jrkoupe]

..so let me ask......

all I can see on my carbs( still on car)..is 40dcoe/tipo 151..

how can I confirm if it is a matching set?...

what is this 15/16 stuff?

[zinz]

+1  on the idle mix/adjustments from Chris.  If your idle adj screws aren't making a significant change in how it runs, the jets aren't sized properly.

 

Now... Who's signature says, "most of your carburetor problems are ignition related" ?  I think I'm going to have that made into a sign for my garage...

 

I don't think you're setting enough timing advance...  I know because I've been fighting my own car now for weeks. 

 

My stoopid distributer is slipping and causing poor running at low rpms.  I'll set it to what my engine loves, 33 degrees at 2000 rpm, (I know, that's a LOT of advance, but my engine loves it) and it runs great...then the damned thing will start to run poorly at low rpms (idle, or coming to a stop after running hard, everything seems to "load-up", coughing and such and running rich)  I'll return to the garage, put the timing light back on it annnnnnd... timing has slipped 5 degrees or more! The other day it was acting up again and timing light showed 27.5 degrees... pew. Put it back at 33 degrees?  BRAAAAAAAPPPP!!!!!  Awesome.

 

Plugs look just like yours, and black soot all over the rear of the car from the tailpipe.

 

Why is my dizzy slipping? I'm tightening it VERY tight.  It's a replacement unit from Ireland and I believe the O-ring is too big.  It was quite difficult to install (others have had this same issue and Andrew has chimed in about the problem of two different-sized O-rings.)  My theory is the too-thick O-ring is not squishing enough to allow the dizzy flange to properly secure the distributer, allowing the distributer to rotate ever so slightly under load. 

 

Whatever the case may be, when it's timed correctly, it runs like a scalded ape, when the timing is not advanced enough?  It runs like crap, especially at lower rpms.

 

As for your fuel bowl level? I fought that same problem earlier this year...

http://www.bmw2002faq.com/topic/150821-engine-bogs-on-decelleration/  (the ignition set up in my initial post has changed now)  The last entry explains how I adjusted the fuel level until I got no fuel-bog at idle and still made good power at WOT.  My timing wasn't advanced enough back then, either. 

 

I think you are very close on your fuel level adjustment, but every setup is different and settings in books should only be used as a guideline.  I'd suggest lowering your fuel level to achieve good idle, then make some WOT runs on the highway and see if she leans-over (obviously be careful not to run too long if it gets too lean.) If too lean at WOT, readjust to find the happiest setting of good WOT power and proper idle.  (of course, this is after changing your timing )

 

Good luck!  Keep us posted; I hope you solve it soon!

 

Ed Z

 

 

 

 

 

 

 

 

[TobyB]

 

If your idle adj screws aren't making a significant change in how it runs, the jets aren't sized properly.

OR your throttle plates are too far open, as in, it's running on the transition ports.

 

This is easy to check- get it idling, switch off, and then pop off those cover screws over the transition holes.

 

If the inboard hole isn't COVERED by the brass throttle plate, it's running on the transitions, and you need

to do something to get the idle air flow down.  Which DOES bring us back to timing and fuel level, doesn't it?

 

hth

 

t

 

 

ps, Ed, mark your housing to see if it's REALLY slipping.  If it is, it's probably vibration- induced.  Go to your local o-

ring vendor and find something that's a bit thicker than the groove is deep, and you'll probably solve it.

[chrisrouse]

Felix,

 

I've never seen a bavaria mechanical fuel pump create too much pressure for a set or DCOEs. 

 

Timing ADVANCE is only part of the ignition system as a whole. 33 degrees at 3500rpm- no more. I've seen hot motors with DCOEs like a little LESS, actually (depending on fuel/ temperature/ mercury in retrograde).

 

What is the static timing at idle? What is the total advance? if you have access to an adjustable timing light, can you plot the advance curve?

 

Have you wiggled/tugged on ALL of your ignition wires including wires to the coil with the car running, looking/listening for changes/arcing/zapping yourself?

 

My car idles happily at 850, with the idle screw turned in maybe 1/8th of a turn. Each Barrel sucks at 4.5-5 after syncing the carbs and air bleed screws. Pulling 7-8 means your motor is running at around 1200 rpm (I think), too high for idle adjustments/ baseline setup.  

 

Is your compression good? Dumping so much fuel down the cylinders can wash the cylinder walls and and rings, lowering compression and causing poor combustion. Maybe try a compression test, then a wet compression test (with a tsp of oil down each spark plug hole). 

 

NEW plugs, NEW floats, NO questionable ignition ANYTHING, verify that the needle valves shut off the fuel supply, and try again.

 

Weber DCOEs are not a "dark art", they're a science.

[zinz]

I'm also with Toby on the throttle plate being open too far, which would negate any effect of the carb's idle circuit. (your linkage is allowing complete closure of the throttle plates?) At the same time, make sure your linkage has a stop that keeps it from over-rotating at WOT.

 

Thanks for the tip, Toby, I'll mark the dizzy and the flange and see if there is actual movement. This is a brand new unit (IE sent a replacement for an early one that leaked oil like mad) I've not been driving the car a lot these last couple months and have been struggling with this timing-creep for several weeks.  Blunt sent me an O-ring (I'll compare with what I have now).

 

As for my timing?  like I say...everyone's setup is different.  I think my engine can tolerate all that advance because of the flattop pistons.  Set it at 33 degrees at 2000rpm and she will idle at 900rpm (though it's lumpy) but the throttle response is instant and pulls hard through progression and into upper rpms. Plugs will be a nice caramel color.  Retard it even 3 degrees and low-Midrange goes flat, poor running at low rpms and plugs will get sooty.

 

Ed

[TobyB]

 

 

Weber DCOEs are not a "dark art", they're a science.

Once you get them responding to inputs, they start to resemble science.

 

Before that point, there are so many unknowns in the equations that sometimes you NEED dark arts to get them going right.

 

I respectfully put forth, as an example, a Spanish- made carb with one main jet well machined 5mm too deep...

 

new plastic floats that varied by many grams...  a brass float that leaked from new...

spark plug wires that came apart internally, producing sypmtoms like the OP has...

a mechanical advance that would suddenly go 'all in' at 1400 rpm, but not drop back until 800 rpm...

 

but yes, eventually, you start to figure out how it all works, and you can cut fewer chickens....

 

t

[felix_666]

Thanks for all the help everyone.

 

Today was painfully slow and unproductive. I feel like I'm going backwards. 7 years of restoration and this is a true test of my patience.

 

 

 

I don't think you're setting enough timing advance...  I know because I've been fighting my own car now for weeks. 

 

 

 

OR your throttle plates are too far open, as in, it's running on the transition ports.

 

 

I'm also with Toby on the throttle plate being open too far, which would negate any effect of the carb's idle circuit. (your linkage is allowing complete closure of the throttle plates?) At the same time, make sure your linkage has a stop that keeps it from over-rotating at WOT.

 

 

 

IDLE ADJUSTMENT

I think you all must have missed my comments regarding the throttle plates on the previous page of the thread. To summarise, here is a picture at idle, I believe this is pretty close to where you want them?

 

 

STARTING

Once the car is started, if it stalls, its very difficult to get the engine going again, even when its warmed up. I believe its because the plugs are being fouled/wet. This has been an ongoing issue, like having the cold start circuit on, yes I have checked it several times.

 

IDLE JET

I changed the idle jets to 50F8, which made the idle mixture screws a little more responsive.

 

TIMING

Timing at idle was previously at 10*, today I tuned it by ear, increasing the advance until the engine stumbled and then backing it off, its at around 12*, I will need to check it with the timing light. Adjusting the timing helped with smoothness. The engine will not operate with any more timing. As stated earlier everything is new, including a rebuilt/curved dizzy.

 

 

REGULATOR

The regulator was leaking fuel from the inlet side so I had to go without it, not sure why, I assumed there was no need for thread tape as they are tapered threads. I don't understand what happens to the excess fuel with these in/out regulators?? The thing sucked, why why why.

The fuel pressure without the regulator is about 3.5-4 psi.

 

 

FLOATS

I rechecked the static specs, currently they are at 8.5/15mm. HOWEVER, the wet test came back at about 24mm.

What is the adjusting procedure of pulling the fluid level into spec, do I gradually increase the "shut off height"and maintain the same "drop" height, eg.

9/15mm

9.5/15mm

 

As it can be seen the below picture I have excess fuel, I'm not sure if this is because the floats aren't quite right, or the pressure is too high, but I'm pretty certain this is the reason why I'm so rich and the car is a real pain to start if it stalls.

 

 

 

The excess fuel, which is hard to see in this pic, is the reason why I think the car is running rich, poorly and REALLY hard to re-start.

Edited September 19, 2014 by felix_666