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Weber DCOE 37mm choke / Carb Coughing-Sneezing  Rating:  Rating
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 Posted: 12-04-2007 02:13 am
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discogodfather
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Hello all,

I find myself floating between 36mm chokes and 38mm chokes on my DCOE setup.  I vaguely remember hearing about a rare 37mm choke for the webers, but can't seem to find them anywhere.  I know they are more common for the Del's.  Anyone seen the 37's for a DCOE?

My setup seems to run great but it sneezes and coughs under hard deceleration in most gears.  I have modified the timing a few degrees and the problem gets a little better when I advance the inital timing. 

One possible reason for the issue is a too light pump jet spring?

This is my setup, its a high compression 2 liter with a flowed head and manifold, headers:

Emulsion Tube                           F3 or F4
Main Jet                                    125
Air Corrector                               170
Idle Jet                                       55 F9
Choke                                        38
Auxiliary Venturi                        4.5
Pump Jet                                    55
Pump Exhaust                            40
Stroke Pump Actuator Rod        14mm
Float Level                                8.5-15mm

NOTES:
Next to lightest pump jet spring



Thanks,

Chris

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 Posted: 12-04-2007 03:34 pm
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Judson Manning
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Chris,

I had a problem with 'sneezing' carbs when I used the double o-ring anti-popping spacer set-up and too rich of jets.  Replacing the o-rings with regular gasketing material was one step in solving my problems the other was ensuring proper atomization to keep droplets of fuel from condensing on the manifold walls.

Looking at your jettings, this is probably the most lean set-up I've seen run on a 907 (which I think is good!).  Most people begin with the Spec 9 (160 main jet) which I find to be ridiculously rich even in a racing application. 

On my 2.2 I'm drifting betwen 135 and 138 mains with 170-190 A/C and 55-58 idle jets and 36mm chokes.  EGT and O2 readings still say I'm running too rich, but that may be a function of the cams I'm running.

The one exception is your pump-jet at 55.  The Spec 9 lists a 60 pump jet while I've had very good luck with 40 and 50 pump jets on my Dellortos.  A 45 pump jet is listed for most applications and is where I'd start.  Too much raw fuel being spewed directly onto a hot intake valve can't be much fun!

You didn't mention what cams were mated to that flowed head and manifold.  It could be the carb-manifold-cam-head-header combination isn't quite optimized.  My first thought is the 38mm chokes could simply be too big for a street 2.0.

Another thought would be a poorly closing intake valve.  After you play with the pump jets and chokes, it might be worth checking to see if the intake valves are properly shimmed.  Worst case, you could have a burned intake valve.

Judson

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 Posted: 12-05-2007 01:46 am
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discogodfather
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Great info as usual Judson, thanks.

I was shocked myself when I realized just how lean the mains where.  I just hope the combo of lean/ with a rich pump jet didn't damage the valves or seats (stainless $$).  I'm going to run a leakdown test to make sure.  I'll check the shim too.

It's funny that you mention the anti-popping setup, that is extremely interesting to me.  Do you mean just go with a simple flat gasket instead?  I thought these things where developed to stop the problem of sneezing and coughing?

My cams are still somewhat mysterious.  They are a modified 104 stlye profile ground by Elgin cams.  The previous owner spec'd them out but never gave me the actual duration, lobe centers, etc.  All I know is that its a great top end cam, with slightly better torque than you would expect from a 104. 

I was able to finally find 37mm chokes through an ebay store. 

http://stores.ebay.com/carbpartsdirect

It lists their location to be Gilroy, CA which makes me think this might be the storefront for Pierce Manifolds. 



My new setup will be:

Emulsion Tube                            F4
Main Jet                                    150
Air Corrector                              170
Idle Jet                                       55 F12
Choke                                        37
Auxiliary Venturi                         4.5
Pump Jet                                    45
Pump Exhaust                            40
Stroke Pump Actuator Rod          14mm
Float Level                                8.5-15mm


Thanks,

Chris


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 Posted: 12-05-2007 07:10 am
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Jensen Healey
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It's very difficult to tune Weber/ Dellorto carburetors without a measuring device like a co analyzer from Gunson or an oxygen sensor and gauge. Mechanics in the '70s were supposed to adjust the carbs based on co readings. Without the proper tools It is unlikely to achieve the ideal tuning. Don't ask how I know.

Kurt

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 Posted: 11-27-2013 04:15 pm
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atgparker
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Hey Chaps, I have a pair of Weber 45DCOE9's on 11602 and I have been experimenting with the float height. I noticed that the 8.5mm is specified in your lists and on a lot of literature. I tried that 8.5mm height setting this week and it definitley is wrong for my carbs which are older units with brass floats and only three progression holes in the throats were the throttle plates swing by as you come off-idle. Lots of popping and back firing as I roll the throttle back to idle and poor accelleration off idle til I get above 2500 RPM then it would get past the progression and into the main fueling circuits. So, I managed to stumble upon and took a look at the Weber DCOE shop manual which is in Italian with English sub notes. It was on a Lotus web page download link and there is an intersting table that lists float height settings for variuos cars, Alphas and Astons to name a few. For the 45DCOE9 there are multiple float level setting ranging from 5 to the 8.5mm which it seems has a direct bearing on the progression holes. All I can add is that at 8.5 the fuel level is lower in the bowl and thus it is going to lean out the progression hole delivery as the butterflies are cracked open. My car runs like crap at the 8.5mm float height and is like a dream when I set it to 5mm like I discovered this morning with it freshly set at this setting last night. I'm tempted to update the progression holes to four in my bodies as the later DCOE's have one extra hole that is right on the edge of the throttle plate when it is at idle with the idle set screws some were between a 1/4 and 1/2 turn to get the RPM to 900. I'm also running a Mr. Gasket fuel regulator set at 1.5PSI and that seems to be keeping the needle and seat's happy and so far no more fuel on the starter motor.

Last edited on 11-27-2013 04:19 pm by atgparker

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 Posted: 11-28-2013 06:47 am
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subwoofer
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Float height is really an irrelevant measure as it varies too much from float to float, fuel level is what you want to measure. Carb theory is not really my strong point, but the fuel level is actually a powerful tuning tool for getting transition and cruise right. It ties in with air correctors, e-tubes and main jets and can change "everything".

A wideband O2 sensor like the Innovate LM2 is immensely useful for understanding what is happening - if you are not measuring you are simply guessing.

John Connelly (sp?) from aircooled.net wrote a lot about it on the old Innovate Motorsports forum, unfortunately that forum seems to have disappeared.

--
Joachim

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 Posted: 11-30-2013 03:46 am
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atgparker
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Subwoofer,

Just like the float level numbers I did a search on

"DCOE fuel level"

I have found references to 25mm and 29.5mm being the right level for a given application. So I'm going to assume the 5mm float height setting on my pair of 45DCOE9's is the right one as the fuel level seems to be some were between the 25mm and 30mm when measured from the main jet stack hole with a caliber. Is that ever a retched thing to try and figure out as the fuel on the caliper is really hard to see!

11602 it running the best it has yet and idles around 900 RPM when warmed up with 12-14 degrees of advance on the timing.

"Innovate LM2" time to goggle that!

Cheerio

Andrew

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 Posted: 02-14-2014 05:29 pm
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atgparker
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I put one of these in the dash last Sunday, were the clock would have been if it had one!

INNOVATE 3844 MTX-L DIGITAL WIDE-BAND AIR FUEL GAUGE KIT

I knew the car was on the rich side. But now that I have to fix the header flange as it is not air tight, dang it!

My initial drives before the exhaust pipe sealant blew out indicated 11's at idle and 10.3 at WOT. The only time 14.7 was seen happened after the flange on the exhaust opened up and started sucking air during heavy engine braking.

The last tank full produced 13.2 MPG. That's 150 miles burning through 10-11 gallons of fuel.

New jetting gets installed this week end per the recommended numbers in the club zone. Looking forward to before and after number comparisons. I will likely up the float setting to 7mm from 5mm were it is now.

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 Posted: 02-25-2014 05:19 am
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subwoofer
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Feeling sorry for you about the header flange, a real pain to redo (if we are talking head to header flange).

I am guessing that you in certain situation actually experience rich misfires, and as your data suggests you are throwing fuel out the tail pipe rather unnecessarily. The AFRs you experience are rich enough to make fuel wash a problem, where droplets of fuel wash the oil off the cylinder walls and cause liner and ring wear.

By setting up the carbs correctly you can greatly extend the life expectancy of the engine, the reason why even high performance engines of today routinely reach 300k miles instead of 100k miles 30 years ago has very much to do with control of fuel delivery.

I guess no one is complaining when they get longer engine life, better fuel economy and the same or better power - all at the same time!

--
Joachim

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 Posted: 02-28-2014 03:09 am
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atgparker
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Hi Subwoofer,
No the leak is now at the end of the header were it goes into the y collector at the start of the main tail pipe that runs to the glass pack. I already have welded up the flange on the header were it is stud/double nutted to the head.

So, I put in the new jets and set the float height to 7mm. This seems to have made a slight change in the AFR numbers. But the off idle running of the engine where the throttle plates are wiping between the three progression holes is now very popy and very lean in term of the AFR numbers. We are talking moments were the gauge reads 15 and 20. But there is very low load on the engine as I'm trying to do parking lot driving speeds at this throttle opening in second gear. So I think I'll put the floats back to 5mm from 7mm which will raise the float bowl levels and see what that does for the popping.
WAS
IS
Chokes:
36
36
Idle Jet:
55f8
50f9
Pump Jet:
45
45
Emulsion Tube:
F16
F2
Air Corrector:
155
170
Main Jet:
150
140
Float height :
5mm
7mm

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