No response to idle mix DCOE 40s - what would you try next?

[man_mark_7]

I have read through numerous articles here, and pored over the DCOE install FAQ, here's my situation.

 

Installed dual "rebuilt" Weber DCOE 40s on an IE side draft manifold replacing a 32/36 weber down draft manifold.

• Car ran well before the swap.
• 123Ignition (just pulled the vacuum line & capped it) Running about 19deg advance at 1350RPM w/out any vacuum
• Electric fuel pump with fuel pressure set to about 3.25 psi
• Floats adjusted to 25mm+/-1mm below top of the face where the emulsion tubes mount into cover

 

My issue: I don't see any response when adjusting the idle mix screw on cylinder 1. I can turn the mix screw all the way in and RPM doesn't change. For the 3 other cylinders the engine noticeably bogs.

 

What I have tried / confirmed / noticed

• Idle mix screw and port and all internal bores leading to mix screw are clean and in good shape
• Swapped Idle jet and Emulsion tube stack from one side of carb to the other, the idle mix issue stayed with cylinder #1
• Throttle plates on both carbs and on both bores of each carb are, to the best of my eyes, dead on with each other
• Even w/ some strong springs pulling the throttle plates closed I still need to give them a push to get idle to drop below 1200-1300 even with idle set stop fully backed out and clearance between l screw and linkage*
• If I back #1 idle mix screw out more than about 2.5 turns (which is around where the other 3 are set) I start to hear popping in the exhaust (too rich?)
• Vacuum sync meter reads nearly identical on all 4 bores after adjusting linkage between carbs and then adjust one air mix bypass screw on each carb.
• Once engine is warm AFR reads right around 14.7 +/- 1. As I slowly open the throttle and hold RPM at a ~2k it starts to run lean ~17AFR.

 

* - Based on this asterisked item, I think my next step will be to pull the carbs and see if the throttle plates are closing properly. I haven't found any mention of feeler gauge widths, or other tests for throttle plate opening. How closed should they be and how to measure this? They look the same through the progression holes, but I recognize I'm only seeing a 2D view of the plates.

 

What would you try next?!

 

thanks in advance,

Mark

 

[Son of Marty]

Before you pull the carbs check for a vacuum leak especially around #1 if nothing shows' up your just out a little carb cleaner or what ever you spray around.

 

 

PS 3.5 psi is to high for dcoe's try about 2 psi.

Edited September 28, 2020 by Son of Marty

[uai]

Hold a flash light from the trumpet into the carb and open the transition hole cover.

And your High idle is an ignition problem.

[Golfcar]

 Based on this asterisked item, I think my next step will be to pull the carbs and see if the throttle plates are closing properly. I haven't found any mention of feeler gauge widths, or other tests for throttle plate opening. How closed should they be and how to measure this? They look the same through the progression holes, but I recognize I'm only seeing a 2D view of the plates.

 

The throttle plates should be closed. Webers use holes in the throats for idle. If they are not closed you will not be able to adjust the idles screws with much effect. That's why UAI said to look at the transition holes and you need to reduce your timing to get the idle down so the holes will work. Some webers have by pass circuits (my 45's on my E9 do). There is a procedure for setting and adjusting those. 

Webers are hard to learn but run great when correct. 

Pierce Manifolds in CA has 2 part videos on Webers. A great investment for your future sanity. 

HTH's 

Gary 

The old guy! 

[Mark92131]

You could program your 123 Ignition Distributor to match the "026" distributor for the BMW 2002 Ti.

 

1000 RPM - 20 degrees BTDC

1500 RPM - 25 degrees BTDC

2000 RPM - 30 degrees BTDC

2500 RPM - 35 degrees BTDC

2700 RPM - 37 degrees BTDC

 

or the "033" distributor for the BMW 2002 Ti

 

1000 RPM - 12 degrees BTDC

1500 RPM - 19 degrees BTDC

2000 RPM - 24 degrees BTDC

2500 RPM - 28 degrees BTDC

2700 RPM - 30 degrees BTDC

 

or the distributor on the early BMW 2002 Ti

 

1000 RPM - 5 degrees BTDC

1500 RPM - 17 degrees BTDC

2000 RPM - 22 degrees BTDC

2500 RPM - 27 degrees BTDC

2700 RPM - 29 degrees BTDC

 

and see which curve works best for getting your idle down.

 

Mark92131

[coloincaalpine RIP 2021]

+1 Marty.  Vacuum leak.

[man_mark_7]

1 hour ago, uai said:

Hold a flash light from the trumpet into the carb and open the transition hole cover.

And your High idle is an ignition problem.

Thx for the comments!

 

I have looked into the transition hole covers, that's how I concluded the throttle plates were aligned.

By ignition problem, do you mean too far advanced or retarded? What else should I look at?

 

mm

 

[man_mark_7]

1 hour ago, Son of Marty said:

Before you pull the carbs check for a vacuum leak especially around #1 if nothing shows' up your just out a little carb cleaner or what ever you spray around.

 

 

PS 3.5 psi is to high for dcoe's try about 2 psi.

Thx for the comments.

 

I have slowly moved a propane torch all around the manifold gaskets, brake booster line, ends of the carb throttle shafts, about everywhere I could think of, I didn't see any RPM fluctuation. 

 

I'll try lowering the fuel pressure. I have read in several places they like between 3-4, but I'll give anything a try.

 

mm

[man_mark_7]

A few things I forgot:

 

I did a vacuum leak by waving a propane torch all around the carb gaskets, ends of the throttle shafts, etc. - no RPM fluctuation noticed.

 

My jetting looks like this:

 

 

My 123 curve looks like this:

 

 

With Vac settings like this (I just hooked up the vacuum it wasn't when i made my original post)

 

 

 

[man_mark_7]

1 hour ago, Mark92131 said:

You could program your 123 Ignition Distributor to match the "026" distributor for the BMW 2002 Ti.

 

Mark92131

Thanks for the comments! In general, does retarding the curve tend to decrease idle?

[Mark92131]

47 minutes ago, man_mark_7 said:

does retarding the curve tend to decrease idle?

 

Yes...

 

It's also easier to start a vehicle with retarded timing since temperatures and pressures have had more time to build in the combustion chamber so they'll ignite quicker. The downside is that retarded timing lowers engine speed, possibly causing a rougher idle.

[Hans]

Are these Italian DCOEs/ Are you using soft mount gaskets?? Do you have the little washer cups and O-rings on the mixture screws?

[Golfcar]

2 hours ago, man_mark_7 said:

Thx for the comments!

 

I have looked into the transition hole covers, that's how I concluded the throttle plates were aligned.

By ignition problem, do you mean too far advanced or retarded? What else should I look at?

 

mm

 

Yes, when the throttle plates are closed and the idle screws are set correctly the only way to get the idle lower is to retard the timing a bit. This is what is so good about a 123. Bad is they leak oil and then don't work. See my write up about that. 

 

As Hans mentioned the rubber soft mount gaskets that attached the manifolds to the block are not a good thing. They leak. 

[jp5Touring]

35 minutes ago, Hans said:

Are these Italian DCOEs/ Are you using soft mount gaskets?? Do you have the little washer cups and O-rings on the mixture screws?

Just checked my 40's and no o-ring/washer.  thanks not to hijack

Edited September 29, 2020 by jp5Touring

[Hans]

6 minutes ago, jp5Touring said:

Just checked my 40's and no o-ring/washer.  thanks not to hijack

And the coil springs.

 

20 minutes ago, m5bb said:

Yes, when the throttle plates are closed and the idle screws are set correctly the only way to get the idle lower is to retard the timing a bit. This is what is so good about a 123. Bad is they leak oil and then don't work. See my write up about that. 

 

As Hans mentioned the rubber soft mount gaskets that attached the manifolds to the block are not a good thing. They leak. 

Errrrr, actually carb to manifiold but yes, they can be trouble. Some folks swear by them. I swear at them.