Weber 45 upgrade Alfa spider 78 US - Alfa Romeo Bulletin Board & Forums

Reply
 
LinkBack Thread Tools Display Modes
post #1 of 17 (permalink) Old 12-25-2016, 11:22 AM Thread Starter
Registered User
 
alfagk's Avatar
 
Join Date: Dec 2016
Location: Tarpon Springs
Posts: 7
Garage
Thumbs down Weber 45 upgrade Alfa spider 78 US

Hi
I restored an Alfa Spider 2L US version and replace the injection by weber carb 45.
i'm struggling with missing cylinder above 3000 rpm
FYI ignition is brand new electronic , new fuel pump ....
It seems coming from the carbs (that they are also brand new)
the setting of the carbs is
Main jet 160
Air corrector 210

It is like i 'm losing one or 2 cylinders when i'm pushing the gaz pedal ...
if i'm accelerating gently on the 2 first stage of the carb it 's ok but when i'm trying to pass to the thrid one (the main) it does not provide power and lose cylinders

any advises ??
thanks
Gerard
alfagk is offline  
Sponsored Links
Advertisement
 
post #2 of 17 (permalink) Old 12-25-2016, 12:32 PM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 5,815
Carbs

Manifold is no issue.
However if you are using the stock cams the jetting is likely to be the problem.
However there are many versions of Weber 45 carbs.
You need to post the exact series which is on the top and the following info:

Idle jets
Main Jets Emulsion tube,
air corrector jets and the choke tube (venturi) size.

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"
Alfar7 is offline  
post #3 of 17 (permalink) Old 12-25-2016, 02:46 PM
Registered User
 
hunttheshunt's Avatar
 
Join Date: Mar 2012
Location: Western Germany
Posts: 704
RJ's guess is most likely to be correct; it seems you're flooding the engine with fuel and I wouldn't continue without having an AFR measuring device installed. No detailed advice possible without the requested carb internals info.

Last edited by hunttheshunt; 12-25-2016 at 02:50 PM.
hunttheshunt is offline  
 
post #4 of 17 (permalink) Old 12-25-2016, 04:10 PM Thread Starter
Registered User
 
alfagk's Avatar
 
Join Date: Dec 2016
Location: Tarpon Springs
Posts: 7
Garage
Arrow

Thanks for your quick responses
carb info : 45DCE 152 199 15
Main jet emulsion tube F16
Main jet 160
Air corrector 210
I don't have an AFR controller ... and never used it .

Thanks again
alfagk is offline  
post #5 of 17 (permalink) Old 12-25-2016, 09:54 PM
Registered User
 
hunttheshunt's Avatar
 
Join Date: Mar 2012
Location: Western Germany
Posts: 704
Idle jet and venturi size figures still missing.
hunttheshunt is offline  
post #6 of 17 (permalink) Old 12-26-2016, 06:47 AM
Senior Member
Platinum Subscriber
 
alfaparticle's Avatar
 
Join Date: Oct 2004
Location: Columbia SC
Posts: 9,742
FWIW, here is my 45DCOE152 setup
progression holes - 4
Venturi - 36
main jet - 140
Air corrector - 170
Emulsion tube - F16
Idle jet - 55F9
pump jet - 40
bleed back - 40

My motor has race cams. I would expect the fuel jets to be smaller with stock cams and/or smaller venturis.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
alfaparticle is offline  
post #7 of 17 (permalink) Old 12-26-2016, 07:33 AM Thread Starter
Registered User
 
alfagk's Avatar
 
Join Date: Dec 2016
Location: Tarpon Springs
Posts: 7
Garage
idle jet 70 F 8
venturi is 36

i found also 2 accellery venturi loose moving inside the carburator ... I may explain part of the issue
however do you think the setting is right for an 1978 2 Liters USA version ?
Thanks for you help
Gerard
alfagk is offline  
post #8 of 17 (permalink) Old 12-26-2016, 08:02 AM
Registered User
 
VabeneGTV's Avatar
 
Join Date: Dec 2011
Location: Massachusetts
Posts: 683
Just wondering why this thread is in the Picture thread, should be in Technical under carbs, etc. also judging from alfaparticle's response that he is using race cams and his jetting is much more conservative then yours, you are most likely way to rich! Just my 2 pennies.
VabeneGTV is offline  
post #9 of 17 (permalink) Old 12-26-2016, 02:14 PM Thread Starter
Registered User
 
alfagk's Avatar
 
Join Date: Dec 2016
Location: Tarpon Springs
Posts: 7
Garage
Good catch !! first time i'm using this Forum and I made a mistake

Thanks
Gerard
alfagk is offline  
post #10 of 17 (permalink) Old 12-27-2016, 06:01 AM
Senior Member
Platinum Subscriber
 
alfaparticle's Avatar
 
Join Date: Oct 2004
Location: Columbia SC
Posts: 9,742
70F8 is enormous.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
alfaparticle is offline  
post #11 of 17 (permalink) Old 12-27-2016, 08:11 AM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 5,815
Carbs

If you are running stock (USA cam) then you are not close to correct jetting. Ed is running a pair of cams that in race engines are making over 215 HP. Yet with correct cam timing and his efforts at Carb tuning it is a totally streetable driver. Listen to his advice.

First be sure your Aux Venturies are positioned correctly.(The fuel inlet goes to the upper inside position)

The correct jetting will be "about" this:
F-16 E tube
125 main jet
180 air corrector
idle jet 50 F8
accelerator jet 30
pump bleed back 50

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"

Last edited by Alfar7; 12-27-2016 at 08:38 AM.
Alfar7 is offline  
post #12 of 17 (permalink) Old 12-27-2016, 09:14 AM
Registered User
 
GTA R's Avatar
 
Join Date: Dec 2010
Location: Yorkshire, UK.
Posts: 464
Garage
The other item which is key to the results are the chokes. What size are they ?
For a standard engine, you should not be running any bigger than 32mm.

The 45's are really too big for your application, you should be running 40DCOE's on a standard engine. You will find it almost impossible to find 32mm chokes for 45's, I've only ever seen one set in 10 years, whereas 32mm are standard on 1750 & 2000 euro engines.
The 40 DCOE's are good for up to 165 / 170 bhp, and can be choked up to 36mm.

To give you an idea, my last GTA Rep ran 40 DCOE's on 34mm chokes on a two litre with extensive cylinder head mods, and much better camshafts, and gave 165 bhp.
I ran it on 45 Dellorto's to start with on 36mm chokes, but it was far more drivable on 40's and smaller chokes.

As others have said above, the jetting is way out too.

If I were you, I'd sell the 45 DCOE 152's and buy a pair of 40 DCOE 151's, much more suitable for your car, unless you're imminently considering modifying the engine radically, with extensive porting, higher compression, maybe bigger inlet valves, performance cams etc.

You could offer to swap with cash your way for a pair of 151's, as 45's are more valuable than 40's, provided they are in a similar condition.

GTA R
Giulia Ti Super Rep yet to finish. BMW 2000 NK to Ti spec
GTA R is offline  
post #13 of 17 (permalink) Old 12-27-2016, 12:13 PM
Senior Member
Platinum Subscriber
 
alfaparticle's Avatar
 
Join Date: Oct 2004
Location: Columbia SC
Posts: 9,742
Quote:
If I were you, I'd sell the 45 DCOE 152's and buy a pair of 40 DCOE 151's, much more suitable for your car, unless you're imminently considering modifying the engine radically, with extensive porting, higher compression, maybe bigger inlet valves, performance cams etc.
I agree. My motor made 169 HP with 40DCOE116/117 "emission" Webers with 34 mm venturis and stock mufflers.
I now have 45DCOE152's, 36 mm venturis and a less restrictive exhaust and the motor makes more top end power but the fuel consumption has gone up from about 23 mpg to about 18 mpg and the response below 3000 rpm is not as good.

Ed Prytherch
79 Spider
85 GTV6 3L
76 Suzuki GT500

A little government and a little luck are necessary in life, but only a fool trusts either of them. - P.J. O'Rourke
alfaparticle is offline  
post #14 of 17 (permalink) Old 12-27-2016, 12:24 PM
Registered User
 
hunttheshunt's Avatar
 
Join Date: Mar 2012
Location: Western Germany
Posts: 704
Quote:
Originally Posted by GTA R
The other item which is key to the results are the chokes. What size are they ?
Post #7 says: 36mm.

Quote:
Originally Posted by GTA R
You will find it almost impossible to find 32mm chokes for 45's, I've only ever seen one set in 10 years, whereas 32mm are standard on 1750 & 2000 euro engines.
May be you watched over 10 years the wrong websites; 1600 GTA Stradale even had 30mm chokes as standard in 45's. No problem to buy them in any Weber specialized shop; starting from 30mm:

45DCOE - Webcon UK Ltd
hunttheshunt is offline  
post #15 of 17 (permalink) Old 12-27-2016, 07:54 PM
Richard Jemison
Platinum Subscriber
 
Alfar7's Avatar
 
Join Date: Apr 2005
Location: Pensacola, Fl. U.S.A.
Posts: 5,815
Venturies

If I wanted smaller choke tubes I would call Pierce manifolds and order them as they are available from 28mm to 40mm.

No reason to go to smaller carbs, It`s all in the tuning. The std carb on the GTA was 45 DCOE 14 with 30mm chokes.

As to cams, widen the LSA. If you are at 104 on the intake move the exh to 108..
Some old threads on the same subject:

Weber 40s or 45s?

http://www.alfabb.com/bb/forums/carburetors-fuel-injection-air-intake/59786-venturi-size-post503983.html.

Richard Jemison
RJR Racing

To view links or images in signatures your post count must be 0 or greater. You currently have 0 posts.

"When you are dead you don`t know it.
Only those around you are distressed.
Same with stupid"

Last edited by Alfar7; 12-27-2016 at 08:12 PM.
Alfar7 is offline  
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Alfa Romeo Bulletin Board & Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in









Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

 
Replace with
For the best viewing experience please update your browser to Google Chrome