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Weber 40 DCOE 18 throttle problems on 73 Midget

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scubabatdan

scubabatdan

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Hi I am new to this forum, I have a 1973 Midget I recently bought that came with a Weber 40DCOE18 carburetor. The 74 is awaiting restoration.

Problem: When I do a “stomp test” rapidly increasing acceleration from an idle, the engine bogs immediately, sputters and lightly backfires. If I slowly accelerate she will run up to red line no problem. When driving she runs fine except when I get on her from a dead stop/idle. No problem during slow shifting and acceleration or top end.

Here are my specs for my 40 DCOE 18 Weber:
30 = choke size
4.5 = auxiliary venturi
125 = main jet
170 = air corrector jet
45/F9 = idle jet
40 = accelerator pump jet
50 = accelerator pump discharge
Soft mount dual o-ring seals
Idle screw 2 turns out produces best idle

Here is what I have checked:
Float distance touching ball not depressing 9mm, fully extended 15mm.
Fuel pressure 2.2lbs
Auxiliary venturis fully seated
With carburetor off, actuated throttle lever, got 6 foot steam from both throats
Progression holes clear and butterflies are forward of progression holes, and even in position and movement.
With engine warm and choke off she idles at 950 rpm

Here is what I have done:
Checked timing, adjusted 1º increments from 8º BTC to 0º throttling up in-between adjustments and does the same thing. Best timing was 6º.
Check vacuum advance, no hole in diaphragm and runs smoother when connected, no holes in line.
Complete tear down and blow out of all jets and carburetor lines (actually runs a little better)
Replaced fuel filer
Pulled hair out
Kicked cat (actually just vented at it)

Any ideas guys??
Thanks in advance
Ðan
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

Welcome to the forum!

As for the Weber prob: The accelerator pump jets aren't goo'd up? Weird.
40 DCOE 18 is the Elan T/C standard carb, BTW!
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

Sounds a bit like too MUCH fuel if it backfires thru the exhaust. You didn't mention the idle mix screws, either. Usually they will be close to 3/4 turn out for a good base setting. Which displacement engine is this thing bolted up to?
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

Hi,
Thanks for the response, the idle mix screws are 2 turns out, at 1 1/2 turns it idles rough, at 1 turn it runs really rough. When I set it for 1 1/2 turn and try and start it cold it will not fire. The engine size is a 1275cc, Number on the engine is 12V/671Z/L 5092.
What else do you need?
Ðan
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

sounds like a to rich idle jet. If your idle screw is more than a turn out it is probley rich.
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

sounds like a to rich idle jet. If your idle screw is more than a turn out it is probley rich.if the butter flys are open at idle it maybe masking the problem,
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

I can't immediately locate my Weber reference books... Jeff (Bugeye58) had posted the 40 DCOE jetting and settings info for a 1275cc at some point a while back, IIRC. Hang in there Dan, we'll see if we can sort it. /bcforum/images/%%GRAEMLIN_URL%%/thumbsup.gif


EDIT: Forgot to ask: When you had the beast off the manifold and hit the throttle linkage, it should IMMEDIATELY squirt that six-foot stream. Just touching it would do it. If there was ANY "lag" there could be an issue with the pump linkage inside.
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

OK there didn't seem to be any lag when I had the carb off, when I hit the throttle I got an immediate stream of gas from both throats. Double checked the idler jets 45/F9's both clear.

Here is a twist hehe I started it with half choke, started right up. waited about 7 min until she was getting warm idled up to 3500 rpm and mashed down on the gas, did the same thing as from an idle it bogged down. Thought the main jets kicked in at 2500 rmp?

Too much gas?

Where's that cat...

Here is a picture of my problem child:

100_0262.jpg
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

If it's idling at under 1K I think the blades are cracked about right.

Dan, what's holding the venturi in place? The 18's have a large I.D. at the entrance to accomodate air horns, held in with tabs and nuts. If the venturi are NOT held with the sleeved horns they will "rattle" about in the bores and not seat properly.

I'm just thinkin' out loud ATM.
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

Backed off the set screw until the thottle lever touched the carb body then reversed 1/2 turn. can't see them through the progression holes. Would have to take it off again to see. But set up the initial butterfly position from an article online.
https://www.carburetion.com/Weber/Tech/dcoe_adjustment_layout_typical_i.htm


Here is what I found at
https://www.teglerizer.com/dcoe/dcoepictures.htm

Bone stock 1275cc A engine
Choke 34
Aux. Venturi 3.5
Main Jet 145
Emulsion Tube F2
Air Jet 190
Pump 50
Idler Jet 50F9
Ex.Valve 50

Might have to order some parts.

Ideas?
Thanks!
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

Actually when I took the filter off the first time they both about fell into my hand. I have since checked to ensure the spring clip on the aux venturi were seated properly and fired her up with out the filter in place and put a finger on each aux venturi to ensure seating and it does exactly the same thing, bogs down.

Still scratching head /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
Ðan
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

Ok, this got me to thinking of bouncing the numbers against what the stock 1275cc engines had on teglerizer's web site for the DCOE, the emussion tubes were the common link (F2's) Mine are F11's, not sure but this might be it.

What do you think guys?
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

scubabatdan said:
Here are my specs for my 40 DCOE 18 Weber:
30 = choke size
4.5 = auxiliary venturi
125 = main jet
170 = air corrector jet
45/F9 = idle jet
40 = accelerator pump jet
50 = accelerator pump discharge
Soft mount dual o-ring seals
Idle screw 2 turns out produces best idle

Here is what I have checked:
Float distance touching ball not depressing 9mm, fully extended 15mm.
Click to expand...

The emulsion tube is the least of the differences. ISTR F2 and F11 are VERY alike. The choke size and mains are way off. I couldn't recall off the top so didn't want to take a WAG. The Tegler data is more like what I remember as right for a 1275. 190 air correctors...

The way it is, it seems set up for feeding one cylinder per throat. With your setup each throat is "eatin' for two." You neet to fatten 'er up.
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

So you thnk I should try the following setup and see what happens?

30 = choke size <span style="color: #FF0000"> Change to 34 </span>
4.5 = auxiliary venturi <span style="color: #FF0000"> Change to 3.5 </span>
125 = main jet <span style="color: #FF0000"> Change to 145 </span>
170 = air corrector jet <span style="color: #FF0000"> Change to 190 </span>
45/F9 = idle jet <span style="color: #FF0000"> Change to 50/F9 </span>
40 = accelerator pump jet <span style="color: #FF0000"> Change to 50 </span>
50 = accelerator pump discharge

Ðan
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

You can likely get away with the aux. venturi you have, the idle jets 50/F9 or 50/F8. Choke, main and air correctors need changin' fer sure. And I'd really try to locate a proper "sleeved" arrangement for holding the front of the venturi... They are subject to a GREAT deal of vibration and need to be properly seated. Those cute li'l "clips" are just locators.
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

Ok I have ordered all the parts but the venturi's and the aux venturi's, weber carbs online only had 30 and 32 choke sizes and I did not see aux venturis. I did find a chart for comparing venturi sizes versus engine cc size here : https://www.geocities.com/motorcity/9526/carbs.html
Will continue to look for a 34mm choke.

Will keep you posted.
Ðan
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

WoooHoooo,
Ok I found place here in Alabama that carries DCOE parts:
https://www.paeco.com/
They have the 34mm chokes (Veturis) and 3.5 Aux venturis (The short ones for the type of air filter I have) not the long ones for the air horns. Should be here in 3-5 days.
Will keep you posted!
Ðan
 
Re: Weber 40 DCOE 18 throttle problems on 73 Midg

...this'll be interestin'.
 
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