engine and drivetrain Need Help! Weber DCOEs Running Rich on Mains. Can't Lean Them Out

[Beach_Bum]

Had a chance to check my fuel pressure tonight. Looks like the Pierburg/Bavaria pump is pushing Just under 4psi. From what I've read, 3-4psi is the range you want to be in. Is that correct?

Also ordered some F16 emulsion tubes to try and some IE angled stacks and UNI filters. They should be here early next week.

I'm going to try the 55F9 idles tomorrow and report back.

Edited March 28, 2015 by Beach_Bum

[Stevenola]

Fuel pressure looks good.  Those angled stacks look cool and will sound great.  Pay close attention when you set lean idle with the 55f9, it's a smaller air bleed than f8 and I found on mine that I had to go in rather than out so start by closing each screw a full turn or so then start backing out.  Also pay attention to where it starts to pop without the main jets in vs where the 60f9 did without the main jets (while driving - revving in neutral tells very little about actual driving conditions).

 

What rpm are you idling at?

Edited March 28, 2015 by Stevenola

[Preyupy]

In a 40DCOE you need to run the velocity stacks to hold the Aux venturis centered in the carburetor bores. The velocity stack slides between the O/D of the Aux Venturi and the I/D of the carb bore to keep the centered and stop them from vibrating. The only connection between the venturi and the carb body is that they are pushed together by a small spring that tries to keep them in contact, if it is allowed to vibrate the connection is lost and fuel will not be delivered correctly through the venturi and will just work around the outside of the venturi and run into the engine un-mixed with the air. Also running without the velocity stacks means the air is tumbling when it gets to the venturi and it will not react the same way as it will with the stacks. Try driving it with the V stacks and no air cleaners.

Your idle jet is way too big, I have never found a stock 2 liter BMW engine that needed any more than a 45f9. You need a F9 or F16 E-tube. The F9 tends to be a bit leaner at part throttle and richer at full throttle ( no E-tube is "richer or leaner" overall, they change the way the carb transitions from the idle to main circuit) BTW driving without a Main jet is like putting in a 600 main jet.

My guess as a starting point for jetting is 120 main, 180 Air, F9 E-tube, 45f9 idle, 40-45 pump jet. and the floats back at 12.5mm The 32 mm chokes are about right for a stock 2 liter, 34's might buy you a couple of HP@ >5500 rpm but will cost you in drivability and low end torque. What header are you running? Or are you on the stock exhaust manifold?

[Beach_Bum]

Fuel pressure looks good.  Those angled stacks look cool and will sound great.  Pay close attention when you set lean idle with the 55f9, it's a smaller air bleed than f8 and I found on mine that I had to go in rather than out so start by closing each screw a full turn or so then start backing out.  Also pay attention to where it starts to pop without the main jets in vs where the 60f9 did without the main jets (while driving - revving in neutral tells very little about actual driving conditions).

 

What rpm are you idling at?

Will do, thanks again for all the advice. I'm idling at about 1,000 RPM. My car doesn't seem to like it any lower, even when I had the 32/36 Solex on it.

In a 40DCOE you need to run the velocity stacks to hold the Aux venturis centered in the carburetor bores. The velocity stack slides between the O/D of the Aux Venturi and the I/D of the carb bore to keep the centered and stop them from vibrating. The only connection between the venturi and the carb body is that they are pushed together by a small spring that tries to keep them in contact, if it is allowed to vibrate the connection is lost and fuel will not be delivered correctly through the venturi and will just work around the outside of the venturi and run into the engine un-mixed with the air. Also running without the velocity stacks means the air is tumbling when it gets to the venturi and it will not react the same way as it will with the stacks. Try driving it with the V stacks and no air cleaners.Your idle jet is way too big, I have never found a stock 2 liter BMW engine that needed any more than a 45f9. You need a F9 or F16 E-tube. The F9 tends to be a bit leaner at part throttle and richer at full throttle ( no E-tube is "richer or leaner" overall, they change the way the carb transitions from the idle to main circuit) BTW driving without a Main jet is like putting in a 600 main jet.My guess as a starting point for jetting is 120 main, 180 Air, F9 E-tube, 45f9 idle, 40-45 pump jet. and the floats back at 12.5mm The 32 mm chokes are about right for a stock 2 liter, 34's might buy you a couple of HP@ >5500 rpm but will cost you in drivability and low end torque. What header are you running? Or are you on the stock exhaust manifold?

Thanks for the great explanation. I'm running the IE full stainless exhaust and their shorty header.

[downhillwolf]

Your fuel pressure is good when idle! When engine accelarate fuel pressure builds up, so for future reference buy pressure regulator.
Never run emulsion tubes without main jet, like Preyupy said it's like main jet 600. Run with main jets or without emulsion tubes, air correctors, main jets and emulsion tube holders.
Keep us posted how using velocity stacks with venturi holders works for you.

Edited March 28, 2015 by downhillwolf

[Beach_Bum]

I should have been more specific. When I said I ran it without mains, I meant without the whole emulsion tube assembly.

[Hans]

My understanding and experience is that 2.5-3.0 psi is optimum for DCOEs.I used a pressure gauge to verify output. My car would not be happy at 4.0

[Beach_Bum]

^ Interesting, I'll do some more searching.

So after running the car today I have a couple areas that are very good and two areas that are not so good.

Jetting:

55F9 idle

115 main

200 airs

I hope I can go up on the mains and down on the airs once I put the F16 Em tubes in

Idle screws at 3-3/4 turns out

Idle AFR 12.5

Cruising at 3000 RPM (light throttle) 12.5-13 perfect!

Cruising at above 3000 RPM (65-70 mph light throttle) 11-11.5 not so good

Cruising below 3000 RPM (45-50 mph in 4th light throttle) 15.5-16.5 carbs popping not so good

WOT from roll starts at 12.5 and goes up to 13 before shifting perfect!

So it seems that cruising above 3000 RPM stayed the same, but cruising below 3000 RPM got too lean.

Ugh! Hoping the F16 tubes can correct this

Edited March 28, 2015 by Beach_Bum

[downhillwolf]

Pooping from 2 or less tubes or from all? If pooping from one or two than your carbs are desynchronised...
How did you synchronize them? By looks, vacuum or flowmeter?

[Beach_Bum]

Not sure which tubes are popping, but I've synched the carbs with a synchrometer. Both are sucking at 4 on the meter.

[downhillwolf]

Try adding a throttle really slow, like tightening idle speed screw. Then look at carbs and see wich one poops...
Like i did on mine...

[Beach_Bum]

It's the carb on the left. What does that mean (besides that it's too lean?) Is it not synced properly?

Edited March 28, 2015 by Beach_Bum

[Stevenola]

revving at idle doesnt paint the whole picture because there is no load on the engine.  Go ahead and bump your main jet up to 120 or 125 whatever you have and see if your WOT stays at 12.5 and if your cruise afr gets worse or stays the same.  This will also help with the 4th gear sub 4k light throttle.  Perhaps the leaner e-tubes will help out the middle.

 

bring your revs up to 2500 or so and put your synchronmeter in there to assure you are still synced at higher revs and eliminate a linkage imbalance.

[downhillwolf]

Desynchronizing or bent carburetor shaft, maybe coupling problem... Had problem on mine with coupling problem... When idle, spring hold back one carb more than other and when i gave throttle, one moved to the point where they both started to get open... So this was the point. Also mine 40DCOE19 have only 2 progression holes so problems between idle and main circuit was noticable with pooping.
To see that happens the best is to measure with synhrometer flow at idle at both carbs and slightly above idle...
Try change idle jets from one side of carb to another, maybe idle jets are stucked... There is hundred of options...
This is why i use carbtune and flowmeter for this kind of problems...
On that video i have 55f8 and then replace it with 50f9 problem was almost all gone...

Edited March 28, 2015 by downhillwolf

[Beach_Bum]

Ok, put synchrometer on and revved up and each carb is still the same. Also swapped idles from carb to carb and it still pops, but I can't tell which one it is because it only pops while driving. I can't make it pop while doing it by hand.

55f9 idle

125 main

200 air

Idle screws at 3-3/4 turns out

Idle 12-12.5

Cruising at 3,000 rpm 13.5-14.5 (Spikes into 15s occasionaly) with some popping and surging (is this odd at those AFRs?)

Cruising above 3000 rpm (65-70mph) 11-11.5

WOT high 10s-11

Accelerating through the gears normally 11s

Overall driveability with this setup seems a little worse than with the 115 mains

Edited March 29, 2015 by Beach_Bum