engine and drivetrain Dcoe Tuning On New Engine -

[felix_666]

I'm seeking some on going advice to get my DCOE 40's running better.

 

I've tried various methods for dialing in the idle mixtures:

Start 2.5 turns out, 1/4 to 1/2 turn clockwise in until engine falls away, or for best idle, of leanest idle, or for fastest idle.

Start 1 turn out and turn either way so idle increases (clockwise?) until 1/4 turn each way has no effect.

Start blah blah blah...

• I have a STE BK synchrometer to balance the carbs, but have a hard time reading the display precisely - the needle moves about a bit. It seems to me that the carbs are within 1 unit of each other, 7-8.
• Linkages and brake vacuum were disconnected when adjustments were made
• Timing is set to 10 degrees using an adjustable light, as per instructions, can't get the engine over 3k to set all in timing.
• No knocking noticeable
• I'm pretty certain the balancing and or idle mixture needs adjustment, but when the engine is hunting about it is impossible to adjust the idle mixtures.
• Currently, all the idle mixture screws are about 1 turn out.

 

Problems:

1. Idle is hunting
2. Terrible power up to 3k, haven't gone over due to poor running of the engine
3. Car starts first time when cold, but if it stalls once warm it is a major pain to start again
4. Occasional bit of back fire when driving
5. Plugs are black, wayyy too much fuel.

 

Engine is new, <15 kms.

• 292 regrind from IE
• E12 - 9.5:1 CR - 90mm Bore
• Crane XR700 Ignition
• All new ignition leads, coil and cap
• Rebuilt and weighted dizzy, no vac, 10 degrees at static
• Pump is new, the bavarian model i think, or what ever the high flow low pressure one is.

Carbs were pulled down, cleaned, inspected by a professional, not me, I think I recall him saying he left them rich whilst the engine was new, does this account for the F9 bleed tube?

• 33 chokes

• 125 main

• f16 tubes

• 45 pumps

• F9/55 idle j.

• 180 air

I need to know a proven procedure for setting the idle mixtures, I'm sure this is my problem. I not new to carbs but totally new to DCOEs and multiple carbs.

 

Will measure the floats in the next day, I know someone will ask so I better have an answer eh?

 

Thanks

Will

 

Edited September 20, 2014 by felix_666

[Conserv]

Will,

There's a great deal of information embedded in past threads on this subject, available with the search function, e.g.:

http://www.bmw2002faq.com/topic/151308-best-dual-sidedraft-carb-setup/?hl=dcoe%20setup

Good luck,

Steve

[M3M3]

What book are you using to understand how they work and tune them?

Read the dcoe install faq (article) on this site.

Edited August 17, 2014 by mlytle

[felix_666]

Steve, I have been through many of the 16 pages of threads that are returned when searching titles for "DCOE". I'm yet to come across someone explaining how to set up DCOEs from scratch, specifically the idle jets, please direct me to such threads if you know of said information.

 

Have read the dcoe install faq several times, again, I didn't see anything regarding setup, only parts required, which I have. I am missing something?

 

Using Haynes Weber Carb manual, it's so so, very generic procedures. Balance carbs, turn idle mixture clockwise, half turn at a time, until adjustment has been reached which give the highest engine speed. This is the level of detail for the idle mixture screws. What if your idle wont sit still?

Edited August 17, 2014 by felix_666

[Guest_anonymous]

Then run a compression and leakdown test. DCOE's are not very forgiving with an imbalanced vacuum signal. On my first "rebuild" with the side drafts I discovered an intake valve guide had broken away from the casting.

if just running rich, throw away the f16 e-tube start with an f9 and try a 45f9 idle. Check for vacuum leaks around the throttle shafts also. I run ITG filters, they breath quite well. What plugs are you running? I cannot run less than premium octane pump gas with a similar setup

[M3M3]

yes, haynes is pretty generic.  you need more.

 

from the install faq

Hammill, Des (2003). How to Build & Power Tune Weber & Dellorto DCOE & DHLA Carburettors. Dorset, UK: Veloce Publishing.

 

i have this and a few others,  but this one i have found the best.

 

key on dcoe's is that you can't just follow a check list.  need to understand how they work so you can think through the issues they may have...which are many!  

 

you issue could be many things

vacuum leak

float level

bad carbs (just because they were rebuilt does not mean they are internally matched)  what model are they?  italian? spanish?  from what car?

jets that may have been messed with so that they are not as marked

bad float valve or spring

and more...

[Conserv]

In post #19 of the following, Marshall recommends a book:

http://www.bmw2002faq.com/topic/151308-best-dual-sidedraft-carb-setup/?hl=dcoe%20setup

A recommendation from Marshall can't be a bad thing!

Steve

EDIT: Marshall beat me to it!

Edited August 17, 2014 by Conserv

[TobyB]

Hunting sounds wrong.  Like, either a timing wander or an air leak- which is pretty easy to get with DCOE's.

Are you sure the warm- up fuelling system is fully shut?

 

Setting initial idle mix takes a while, but it's interlocked with idle timing and idle sync AND idle speed.  So I always start

by lashing the valves, then getting enough carb to get the thing to run, with the idle speed screws. 

Then I check sync, and rough that in.

Then I go for best lean idle with the idle mix screws THE SAME, and reset sync and idle speed.  That usually doesn't give a

very even idle, but it's a baseline.

Next, I reset timing, and idle speed again if needed on the idle speed screws, and recheck balance.  Here's where you start to find things

like bent throttle shafts, loose venturis, air leaks and leaky warmup circuits... as well as variations in float levels.

When all that's done, I'll reset each idle mix individually for best idle.  I find a variation of 1/8 to 1/4 of a turn to be pretty normal-

and it usually improves idle quite considerably.  If you find one that likes to be more in (or out) by half a turn or more, there's

probably something not right with that bore, carb, etc...

 

hth

 

t

Edited August 17, 2014 by TobyB

[felix_666]

Ordered that book, will have a good dig through it - How to build and tune...

Carbs are Italian, were previously on a 2002. The jets I mentioned earlier are what I pulled out, front and back match.

The bloke who rebuilt them has had his carb shop since the 80's, I'm hoping he would of picked up on anything that was a miss. I'll eventually take the car to him, but really want to be able to problem shoot myself.

Would like to problem shoot as much as possible before I change things out.

Running 98 octane.

Picking up a float gauge and will search for leaks and check balance again.

Thanks guys for the lengthy replies, really appreciate it.

[felix_666]

@Toby: By warm-up system do you mean chokes? They are not connected but still exist, the springs in them seem tight, so they should be closed.

 

I'm going to try a little more advance, but my dizzy is tight, no movement from the notches in the flywheel when I hit it with the timing light.

 

Have spent all night reading up on DCOEs, going to try and check for leaks, perhaps the smoke method, unless someone has a better method, carb cleaner/butane?

Edited August 18, 2014 by felix_666

[jireland2002]

I suggest you start with the timing.  Set total advance at 33-34 degrees.  You'll need to set it at 3000+ rpm. 

The idle jets are probalby a bit too big.  If the idle is hunting look for an air leak.  BUT first set the timing.

[Harv]

Sounds like thee is something wrong with timing as you said set 10btdc with adjustable timing light. Not trying to be insulting but are you really at 10btdc or did you just turn the timing light?

John

[felix_666]

I suggest you start with the timing.  Set total advance at 33-34 degrees.  You'll need to set it at 3000+ rpm. 

The idle jets are probalby a bit too big.  If the idle is hunting look for an air leak.  BUT first set the timing.

 

Jim, as mentioned in my first post I'm having trouble getting RPM over 3k, which makes makes it difficult to set all in timing. I'll check for leaks and work towards all in timing.

 

 

Sounds like thee is something wrong with timing as you said set 10btdc with adjustable timing light. Not trying to be insulting but are you really at 10btdc or did you just turn the timing light?

John

 

Turn the timing light?? What does that mean?

 

As with any non-stock timing I set the gun to whatever number I need and shoot the TDC mark - which for these cars I believe is "OT", i think. Sound right?

[Hans]

Italian older carbs would use one turn out if memory serves. Fuel pressure regulator is a good idea. I recently found a leaky float that had caused all sorts of weird running. Might be useful to check float levels and give them a shake. But as above, timing is critical. OT is TDC.

Edited August 19, 2014 by Hans

[TobyB]

 

 

@Toby: By warm-up system do you mean chokes? 

 

 

DCOE's don't have a traditional 'strangler' choke.

(to keep terms separate from the different sized venturi 'chokes' that install in the bores)

Instead, they have a cute little carburettor that runs very rich, and the

usual 'choke' cable engages that system more- or less- as needed,

and it enriches the mixture to help warm- up.  When it's 'off'

the pistons sit on pretty precise seats that close them off to the carb entirely,

and remove the 'warm up enrichment'.  It's pretty neat, but...

 

Depending on vintage, those can jam, the linkage can be mis-installed as a result

of changing the orientation of the cable pull, etc etc etc.  So when you have running

problems, it's always good to take that part of the carb apart and confirm that all the

pistons are down and sealing pretty well.  I've had them stick up slightly, had the linkage

be bent and mis- aligned, and seen the 'wrong- sided' linkage hold one wide open.

Might not be related to your problems, but it's worth ruling out.

 

Pat Braden's 'Weber Carburettors' is a good supplement to Haynes....

 

t