Modern Carb Conversion? - Alfa Romeo Bulletin Board & Forums

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Old 11-15-2010, 09:12 PM
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Modern Carb Conversion?

Outside of performance carb upgrades such as the pricey Webers, I've wondered about adding a "pedestrian carb" setup to a spider.

I see manifolds for 2 bbl carbs on ebay from 1300 Giuliettas, etc.

Would one of these, or another, work on an 84 Spider with a modern 2 bbl carb? How hard to do? Advantages & disadvantages?

I assume I'd have to add a non-electronic, adjustable distributor...What else (other than removing the ECUs).

Would other electricals - guages, lights, etc - still function?

Just wondering...Dickson
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Old 11-15-2010, 09:19 PM
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If you're talking about the 84, then the L-jet stuff is a literal piggyback onto a functional system: you can totally remove it and everything like gauges and lights will still work. Motronic is a bit more intregal, but could prolly do the same with a little more effort.

You might get away with keeping the ignition as I 'think' it can operate without the fuel part being connected to the injectors and such. (fuel ECU may have to remain and be powered though, not sure)
Or there's a slew of drop~in electronic and points type ignitions that could be used instead (RML, 1-2-3, etc)

If you could come up with a manifold, (see also:'make'), you might get away with using an off the shelf Holley or simular carb, otherwise you'll need to come up with proper manifolds and suitable carbs. Individual carbs for a bike might do, but they are a little small in the float bowl area.
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Old 11-16-2010, 05:18 AM
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I think that idea come under the "too hard to do" category. Assuming that you don't have to comply with emissions inspections, a Dellorto or Weber conversion is your only reasonable alternative. If you want a good street-able engine then maybe a earlier non-variable cam head with some European cams and Webers would be good, along with a stand-alone electronic distributor. This stuff is fairly easy to find, but not necessarily cheap to do. I can't remember if an earlier head is compatible with the EFI blocks, but Papajam would know. Maybe use the EFI head as well if you can remove the VVT.
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Old 11-16-2010, 07:56 AM
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Ah, the VVT...That's an issue.

Had to ask.
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Old 11-16-2010, 07:56 AM
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Losing the VVT is no problem, the solinoid type can be simply be unplugged and the cam re~indexed while the inertia type can come out with a cam swap, or, if put in the hands of someone competent with such things, (Alfar7 comes to mind), left in there to actually function normally but with it's timing or degree of advance tweaked to more suit the change in induction or to dial in a power curve.

The EFI head will take alternate manifolds to the EFI, but there's a cast~on lug above the #1 intake port that needs to be ground back to give clearance for the older manifolds (prolly deliberate so folks would have to get the EFI worked on rather than just tossing it out for a carb swap when things got creepy) and 2 of the mounting studs need to be changed to longer ones. Otherwise it's pretty much pop~n~drop using the gasket for whichever intake manifold is being put on. (coolant disbursion is different in the manifolds but the service ports are the same on the head. As in a EFI manifold gasket won't work with a carb manifold, but a carb manifold with a carb gasket will work on an EFI head)

There will likely be a fight in regard to connecting the gas pedal to the new stuff though.
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Old 11-16-2010, 11:36 AM
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Just shooting from the hip here...

I'm not sure what your goal is, but, if you adapt just one 2-bbl carb, I predict that you would lose performance, efficiency, and some driveability over the EFI system. All that and it would be a PITA to do - more frustration than tuning the EFI. I see no upside.

Also, as far as carburetors go, I don't think that modern carbs have any advantages (besides parts availability) over older carbs - as long as we aren't comparing them to ancient carbs. Are "pedestrian" carburetors even made anymore?
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Old 11-16-2010, 11:59 AM
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Holley and Edelbrock are still making money building carbs AFAIK, including the not~performance~orietated stuff.
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Old 11-16-2010, 02:09 PM
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Quote:
Originally Posted by Dickson View Post
Outside of performance carb upgrades such as the pricey Webers, I've wondered about adding a "pedestrian carb" setup to a spider. I see manifolds for 2 bbl carbs on ebay from 1300 Giuliettas, etc.
Would one of these, or another, work on an 84 Spider with a modern 2 bbl carb? How hard to do? Advantages & disadvantages?
Quote:
Originally Posted by Slash
I'm not sure what your goal is, but, if you adapt just one 2-bbl carb, I predict that you would lose performance, efficiency, and some driveability over the EFI system.
I think Slash has summarized my thoughts pretty well. My sense is that Dickson is having trouble with his EFI, but doesn't want to pay for all the parts required for a Weber conversion. In theory, a manifold from a 101 normale would fit a 2 liter engine, and a single downdraft carb could be fitted.

But, as Slash wrote, performance would probably suffer. While the 2 barrel Solex - or its Weber (downdraft, not DCOE) replacement would bolt on (well, after the head grinding, stud replacement, and linkage fabrication that others have described), performance would no doubt suffer. That 2 barrel Solex was sized for 1300 - 1600cc engines - for larger displacement carbureted engines, Alfa always (I think) used two DCOE's.

Yea, the cost of two, new DCOE's is a little steep. But by the time you accumulated all of the parts needed to do a single carb installation, I doubt you would be that far ahead cost-wise. And, as Slash wrote, there really is no such thing as a "modern" carburetor. Actually, that term is kind of an oxymoron, sort of like "modern" buggy whip. Carburetors probably reached the pinnacle of what could be achieved with the Weber DCOE. The definition of a modern induction systems is EFI.
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Last edited by Alfajay; 11-16-2010 at 02:13 PM.
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Old 11-16-2010, 08:16 PM
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At Centerline, we are often asked about selling a carb conversion for an L-Jetronic Spider. Often the reason is a car that the owner is having a hard time getting the car running acceptably or has had something catastrophic like an electrical fire. Other times the owner is simply looking for the "romance" and perceived performance benefit of carburetors.

This is just my 40 Lira but I think this is a really *bad idea*.

Let me explain: When converting from Spica > Carbs, you are really making a lateral move in regards to sophistication. When you are going from EFI > Carbs you are taking a huge step backwards.

The few people I know that have done this have not been satisfied with the results. Quite simply, there is more to making an '84 Spider perform like a '74 Spider than carburetors, and this is the crux of the problem.

The other issue to consider is altitude compensation - on a carb setup there is none. Thus, in Dickson's case when you drive from Denver to anywhere else (either up or down) you will probably have to re-jet the carbs.
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Old 11-16-2010, 09:18 PM
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Thanks guys. You pegged it: In a moment of weakness I was looking for an easy way out.

I know and semi-understand carbs from past experience. Not so with EFI.

Must be patient & learn....Not easy for me!
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Old 11-16-2010, 09:33 PM
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Let me explain: When converting from Spica > Carbs, you are really making a lateral move in regards to sophistication. When you are going from EFI > Carbs you are taking a huge step backwards

Joe summed it up perfectly! The L-Jet system is the most anvil simple system on any Alfa, period.
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Old 11-17-2010, 08:26 AM
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Really random tangent:

Joe's 40 Lira
I've seen it a bunch of times, but never gave it much thought til today.
A quick currency conversion....... Yup, 40 Lira really is 2 cents.

Deliberate, or just a lucky guess. The decision is up to you LOL
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Old 11-17-2010, 09:24 AM
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Dickson, FWIW, if you can understand a carburetor, the Bosch L-Jet EFI should not be difficult for you.

You've probably heard this before but I'm going to say it anyway: Click on the link in Tifosi's signature block and read the online diagnostic manual at Greg Gordon's website. Block out some time and go through the procedures outlined in the manual without skipping any of the steps. Think of it as spending quality time with your new best friend.
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Old 04-02-2011, 12:01 PM
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I've owned a couple of Corvairs, which have log intake manifolds that are integral with the aluminum heads. What Corvair people have been doing since the Sixties is cutting off the top half of the log manifold, welding a top plate to accept multiple Weber carburetors. Doing so to an Alfa L-Jet would be similar.

Assuming you live at sea level (easier carb tuning), have or are going to install performance cams and pistons, it seems like you could convert an L-Jet to dual Holley 2 barrel carburetors with some relatively minor fabrication.

-Using the original L-Jetronic plenum, I would simply cut horizontally in half..... or pretty much in half.

-Next install tubing to extend the cast intake runners to just above cut line.

-Cut aluminum plate to cover plenum, with holes for extended runner tubes. Weld cover to original plenum.

-Fabricate dual Holley carb mounts, orienting linkages towards center of car.

-Fabricate mount to support stock L-Jetronic throttle linkage.

-Fabricate linkage to connect L-Jet linkage to Holley linkage.

-Tune carbs.

-I don't know if the carbs will stick above the hood line, but if so, a tear drop blister similar to a 250 Ferrari Testarossa might look good!
SUPERCARS.NET - Image Gallery for 1958 Ferrari 250 Testa Rossa

Holley makes two 2-barrel carburetors; a 350 CFM and a 500 CFM, both for under $300 each. A whole lot less expensive than Webers.

Conversely, it seems like a cheaper way to go from SPICA to carbs using the L-Jet plenum, rather than Webers.
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Last edited by Superflow; 04-02-2011 at 12:19 PM. Reason: To correct spelling.
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Old 04-03-2011, 01:10 AM
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Why not go for a best of both worlds, use individual throttle bodies?Benefits of carbs & EFI in one package.
Use an aftermarket management system, set it up once & you will see around 20bhp increase with much better top end delivery.
You will have the induction raw of carbs without the downside as well.
Just a suggestion.
Ciao,
John
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