engine and drivetrain Weber DCOE 45 Tuning on a lightly Modified Engine

[TobyB]

He has a 2bbl Lynx setup, not individual runners, Lee.

 

And again, in more general terms, the 'breathing area' on a plenum system (either a 1-2 like the Lynx or a 1-4 like the stock downdraft)

has a 'time component'- on a 4 cylinder car with 2 cylinders on one choke, those cylinders both see that 45 mm throttle plate.

Since they alternate, the average FLOW through the barrel doubles, but PEAK VELOCITY through the barrel is no different than if it was individual runners

OR if all 4 were breathing through that one throttle plate.  And PEAK VELOCITY is what the 'chokes' (venturis) regulate most.

 

Corey, get a new seal kit into your carb, clean i out well,  bolt it back on the car the way it is,

get a wideband meter working, and see what happens.  Your idle problems

are NOT choke related AT ALL, and you can mess with the idle air screws and idle mixture screws

and CERTAINLY get it to idle and transition better.

 

There IS no black magic in these things.  It looks like there is, but once you figure out how all the (complicated little) parts

work and interact, suddenly you find that they are very reasonable indeed.  And the wideband is crucial to that-

your ass can't tell that a 35 idle is a little lean and a 45 idle is a little rich, but the WB can, and will, and suddenly that

number will turn a light on in you noggin.  And btw, the 'idle' jet is really a 'transition' jet, as it regulates the fuel to the carb

AFTER you get off the idle circuit and before the main circuit starts to really flow.  So if your 'idle' jet is all that is determining your

idle mixture, then the throttle plates are open just a bit too far.  Open the idle air screw a bit, and try again!

 

The chokes will only come in at higher throttle angles, and if they're too big (I've never played with the Lynx, so I don't know)

then where you'll have trouble is at low- throttle- angle cruising- like, 45 on a side street, or even 75 on the highway.  It doesn't

take too much to keep a 2002 going, so the idle and especially the progression circuits are where the car cruises on the freeway.

And it's the transition onto the main jets that the venturis (chokes) will affect.

 

Pat Braden, Weber Carburetors

Haynes, Weber Carburetors, Including Zenith and SU Carburetors

 

Dense, and you learn by reading, trying, getting confused, re- reading, re- trying, looking at the WB numbers... eventually, the light comes on.

 

It's cool.

 

hth

 

t

Edited February 6, 2016 by TobyB

[CaptJ]

Thank you for the feedback Lee and Toby.

 

For now I'll rebuild it as is but I will definitely keep your thoughts in mind Lee.

 

 

Now for gasket kits. I seem to have found three completely different kits. Not sure which one to get besides getting the 2.00 needle and seat.

 

https://www.webercarbsdirect.com/ProductDetails.asp?ProductCode=92.1047.05M&CartID=1

 

http://www.piercemanifolds.com/ProductDetails.asp?ProductCode=92.3247.05&CartID=2

 

http://www.carburetion.com/_aspstuff/cucart.aspx

 

Thank you!

[Dicks]

In the FWIW department.....  

 

Jetting recommendations from TEP for single side draft Webber DCOE 45

 

34    Chokes
150 Main
180 Air

60F8 Idle
50    Pump

[CaptJ]

Thank you for the info.  I searched TEP's website and couldn't find where you found these recommendations?

[Modifier]

Reviving an older thread. I recently purchased the Top End Lynx kit and installed it on my car. Didn't like the throttle cable it came with so fashioned my own linkage out of left over Weber/Korman parts I had...works very well now. My issue is that I have run through the steps of tuning and adjustment and just cannot get the carb to behave. It will idle well (once warm) and will run fine at slow speed, but once I stomp on the pedal, it bogs down completely and studders. I know it has to be an air/fuel or jetting issue so thought I would ask here. I do have an aspx digital wideband sensor I just installed as well.

 

My car:

E12 head with:

  All casting removed from rockers

  Schrick 292

  Port and polish

Engine:

  9.5:1 pistons

  Bosch black coil

  Pertronix electronic ignition

Intake:

  Lynx manifold with (1) Weber 45 DCOE

Exhaust:

  Stahl headers

  Stebro straight pipe with resonator

  Supersprint exhaust

 

Linkage is smooth and opens to full throttle

New NGK plugs

New Filter King resonator/filter set at 3psi

New fuel line (electric fuel pump in trunk)

Intake came with new gaskets as well as soft mount gaskets for carb

 

Weber carb came in the box with the following: (Note difference in sizes that are recommended in Dick's post just above)

Choke 36

Main 145 F16

Air 155

Idle 55 F8

Pump 45

 

Before I start throwing new jets at it and/or tuning any more I figured I would ask your expertise. Oh...as far as air filters go...I have run it with the air horns provided in the kit and with/without the screens. I also have a set of curved Corsa Velocita stacks with the red filter. If I don't use those I plan to run Uni pod filters or a Itg Megaflow filter.

 

Thanks!!!!

Greg

 

 

[Hans]

Did you check timing, float level. Are you using pressure regulator?

[TobyB]

Quote

I do have an aspx digital wideband sensor I just installed as well.

 

So, then, when it misbehaves, what does the wideband say?

 

If you're going lean, it's very likely a fuel delivery issue.

 

If it goes lean immediately, the carb's not delivering enough.

If it goes lean 30 seconds later, the fuel pump's the issue.

 

hth

 

t

 

[Modifier]

@Hans - Timing was fine with previous setup, but can check. Yes, regulator is set to 3psi per another thread I on here I read...let me know if it should be different.

 

@TobyB - Ha!...no I don't think I even tried to read it when it bogged down. I will do that!

[Modifier]

Okay, finally got the time (and the garage wasn't freezing) to play around with the car today. I installed a set of Uni pod filters on the velocity stacks that came with the Weber 45. They fit well and I know will have proper filtration. Got the car started and warmed up and got the following:

 

At idle the wideband fluctuates around 12-13.5. It doesn't seem to sit steady, but that could be the fact I got the readout instead of the gauge and it fluctuates more.

 

When I go to FOT the car bogs down immediately and the read-out jumps to 19 (this is lean correct?). The car will die if I hold it.

 

So...what to do next? If lean, then up the fuel pressure?...it is at 3psi now.

[Simeon]

Pump jets?

[Oldtimerfahrer]

Hi,

Pressure alone is the wrong approach in any case, you will only force the needle valve to leak and overflow the bowl. The only "pressure" you might want to check is the level of fuel in the bowl. I see that you have considered it, but how did you measure it? Best method is the "in place" method of measuring via removing the jets/emulsion tubes and checking the actual level of fuel in place after the pump has filled the fuel bowls and closed the valve. You will have to google that though, I don't have a good description but I have used it a long time ago. The method with removing the cover/float assembly and measuring the distance of the float to the valve and float to maximum opening position is the method described in the Weber handbooks and most often used. If the tabs or float arms are bent though, then the measurements can also produce the wrong result with both methods I would guess. 

As Simeon said, if the pump jets are the incorrect size or the pump is not working at all or not delivering what it should it will run lean. If opening the throttle quickly induces it and it stays normal when slowly opened, that would point to the operation of the pump jet. The pump jet only delivers a certain enrichment for a brief period to avoid leaning out under acceleration, but its operation is limited so if the engine never recovers then that might also not be the cause. But as noted, if the float level is incorrect, that would lean the mains and reduce the operation of the pump jet, they share the same fuel from the bowl. I would first check the float level, then check the pump jets for correct operation and check what size they are. There are methods for measuring the operation of the pump jet , but I have only check whether they work at all. I remember seeing something somewhere about spray pattern and distance, but someone else can probably provide much better input there.

Andrew

Edited December 24, 2016 by Oldtimerfahrer

[TobyB]

What happens if you roll into it?

With a DCOE, it responds differently to a gentle throttle than a stab.

 

The pump jets help get you up to speed,

but then the mains keep you running.  Float level first,

and then make sure you have enough fuel to keep the float bowl filled.

If the car dies at WOT, this almost always means not enough fuel in the bowl,

or way too much getting through somehow- flooding will do it, but

that's pretty unusual...  and your wideband says you're starving.

A temporary fuel pressure gauge will tell the tale- if you have even 1 psi,

you have enough.

 

Here's what I do to diagnose a lack- of- fuel problem- run it WOT until it dies, switch off immediately,

then check the fuel level.  On the DCOE, it's super easy with a dipstick down the jet cover.

If the bowl's dry, then start looking at your fuel supply.  Starting with the little screen in the inlet...

 

hth

 

t