[AutoLinc]

I have a small shop with an excellent tech servicing a wide range of older sports cars, but we have limited Alfa experience. We recently took in a '73 GTV 2000 with Weber 45s and a header. We're the third shop to try to sort this car out. The car stumbles badly under any load, and backfires a bit when run at 4000 with no load. Compression is 175 psi. The car has an MSD 6BTM ignition (more suitable for turbo/supercharged, but should be OK for this) putting out a very strong spark. The plugs indicate lean running. What would be the recommended jet sizes for Idle, Main, and Air correction for this set-up? Any other ideas?

Thanks,

 

[bellagt]

I'll choose Door #3 and Other Ideas...

Have you checked for induction leaks between the Webers and the head? With the engine running, spray some starting fluid along the intake manifold mating surfaces and see if there are any changes during idle or rev up. If the roughness goes away, then you have an induction leak...

 

[kpc655]

check the timing. probably wants more advance than the stock settings would call for. i run my race motor at 30 degrees total and my street at 26. far more than the stock advance curve gave it. without this..they backfired..and generally ran like crap.

 

[flivesay]

45's are hard to set up on a 2l unless you have the magic jet, venturis and choke sizes. After you've checked for leaks and made sure the mechanical and electrical timing is correct hopefully the weber gurus will chime in. What jets and venturis are you running now?

 

[Sean Lindsay]

Hi,
Dish washing fluid, should point up leaks --too ! Dcoe 45 can be jetted to a stock 2000, but, unless the engine is very modified -- DCOE 40 are the choice. Headers should make no diffrence. What you have is a stocker, with-- over size carbs ! Check, that all your spark plug leads are in good shape. I found starting the car in the dark with the hood open is informatve (broken leads -- light up ). Check the ditributer for wear .

Old Alfas gas tanks, rust and send rust into the carbs, causing studder --check float bowls and filters. Both Webbers, are supported by an arm, that comes up from the rubber and steel engine mount . This support systen can get lost -- over time ! Check the rubber insert in the arm (bottom ) too. This support must be functioning properely-- to tune !

Dcoe 40 with the stock Jets ( from a manuel ) would be easier. There are two books (tuning/theory) on Webbers --depends how far you want to go !

 

[PSk]

And what fuel pump is it running? If the standard mechanical one, remove it and ensure that it does not have any restrictions in flow (and then once confirmed fine put back on). I once found one that was a casting flaw and caused the motor to lean out ...

Also did an Alfa knowledgeable person make the headers?. If they are made so they are perpendicular to the exhaust flange face, remove them and throw them in the bin and replace with the original cast manifold. This should not cause the problem you have but will cause a considerable power loss.

I'd put money on air leaks or fuel supply issues.

A rolling road would help a lot. These motors are really simple, but if somebody has just chucked 45s on without running it on a dyno ... how would you possibly know the right jets?

I do hope the manifold and inlet ports were also ported by an Alfa knowledgeable person ...
Pete

 

[AutoLinc]

Thanks

Thanks for your help so far. We'll let you know how this unfolds during the coming week.

 

[Andrew]

More than once I've seen and heard of MSD setups that didn't work well or at all. Can you disconnect the MSD if it'll run without it? I had an MSD 6420 box on a Buick 340 with Pertronix electronic ignition and it ran much better without it.
These are pretty simple engines so the solution ought to be pretty glaring once you narrow it down.
Andrew

 

[Marvin Pansch]

AutoLinc-- If you could find your venturi size and the cam part numbers, I bet there is someone on the BB who has nearly the same setup who would love to share. Also, find your cam centers and publish the cam centerline timing. Very important on single cylinder carbs such as the weber.

 

[gigem75]

Has it ever run right with the currrent setup or did someone buy it and is trying to sort it out? I don't claim to be even a grasshopper when it comes to setting up webers but I have to agree that putting 45's on a stock 2L motor is an excersise if not in fultility close to it if one want's a streetable motor. Who knows it might run great between 5500 and 6500 rpm

 

[Andrew]

The Webers could have any venturis and any jets, so it's really hard to know whether they're right. You could compare to the factory setup (32mm I think) and proper main, idle, and accel jets, and starter and air correctors. 2000s didn't come new 45s, just 40s, and there are some differences.
Andrew

 

[101/105guy]

45s will work fine on a 2.0 with the proper venturis and jets.
Heck, I have 45s on a 1750 and it is great. Great low speed and great at high revs !
Mine have 33mm venturis.

 

[60sRacer]

Putting 45's on a 2L only makes sense if the cams are non-stock, and the head has been modified. Can you post the cam numbers? (part no is on the cams for stock or alternate Alfa cams).

R

 

[AutoLinc]

Thanks

Thanks for all the help so far. My tech is following all your suggestions. I'll report back later in the week. We'll be mounting 40mm carbs from my Alfa Monday, and will have the cam info, etc. available.

 

[Sean Lindsay]

Hello ,
Follow up ! Common books on the topic :

a) Webber Carburettors By : John Passino

b) How to Power Tune Alfa Romeo Twin Cam Engines By : Jim Kartalamakis
c) Factory Manuals ( From Alfa Racambie ) are a better investment .

Additional : Metal Fabricators Hand Book By: Ron & Sue Fournier ( how to on... body work/complete exausts/ Roll Bar's).

Point# 1) : Mismatch between header & head -not an issue. But: An
(exact-- paper) template, made at the head and placed over the mouth
of each pipe -- will show a miss match . A light file -sufices !

Point# 2) Marellie Makes a Electronic Distributer (replaces everything --
especially for Alfas.for Alfas)--Couple of Hundred --easy fix .

Books generally clear up an issue. Autos.not Rocket Science here ! With Modisty now !

 

[Sean Lindsay]

Finally, (over complicated-- extranious to the topic )
Hot cams not likely to cause a studder. Look at hot cams you can see they
are diffrent ! Alfa Racombi or.. should have a chart . You have to cut a nich out of
the head to accomodate the high lobes --no nich, you bend them! Check for it--nitch !
Stiffer double springs good Idea -for hoter stuff ! Hot cams little harder to find--likely stock . Fuel pump (5-7 lbs--check, think ?) Fuel Inject..15 lbs = a problem . Secondary pressure reg. good idea too ! If you change one thing -- often you have to change a lot of others. Know your stuff befour you proceed ---45's makes me suspicious
--they diden' t ! Ps: Carter Super Pumps -- work well if you are need of a pump in the
right lbs. range ! Hot Cams diff. shims & gap-- diffrent ...on &...on !

 

[papajam]

Just to be clear, it is the VENTURI (aka choke) diameter that's important. Whether the carb is a 40 or 45 is irrelevant.

 

[Sean Lindsay]

Ok.
Jim diff. of opinion ! Had Delortos (sp.?). Lots of webber's . A... individual even got a
hold of my Alfa and placed a set of 45 on it (fast one !)" It ran" ..not the best --
my opinion ! Bought new 40 put them on. --at that time my car was stock (rebuilt/restored --by me). Now my Alfa is renginered totally by me (souped up )-- this point . I may reboring the 40's (very precision machine shop) if they could do it
right ! Read Kartaalamakis --for now-- go with him !
My point you can do anything . Question how much time and trouble do you want to go
to. Read quoted (Passini, Webbers) the verribles start to get considerable/ferce .All the
components swops/judgment. Can do it, easier -- 40s look up componets (jets/ven.) . Know where you are at..know where you are going. Other wise, you slip into a quagmire --caos! Built and reengineered for years -- Alfa's---can drive you &%*% --nuts ! Read/think/plan ! Save your time for all the other problems !

 

[60sRacer]

If the car had 45 Webers on it, and that was done right, the intake manifold and intake runners have been hogged out to match. Just bolting 40's in their place will make as many problems as before, as their diameters will not match, and the air flow will be worse than if you kept the 45's. If the 45's were just bolted on and not properly installed, it's likely that the venturi's, idle jets, main jets and air correctors were also all wrong; that would instantly cause the poor running problems. The carbs really must have the proper carb support rod too - it runs vertically from the engine mount.

If the headers and 45's were done correctly, then mitt's possible the carb mounts or intake gaskets failed and are leaking air. Again, that could cause all the problems you describe.

You really should investigate what you have - carbs and its parts (ventures, jets), machined intake and exhaust manifolds, cams, etc. BEFORE you change anything.

Without this info we're just blowing smoke and you're wasting your and our time.

Robert

 

[Gary Williams]

Click here for an excellent link by Dave Andrews on how to set up Webers: Alfa 105 Technical Info

The link will also guide you to a very simple software program that will give you the carb settings you asked for.