Spica to Weber Conversion - Fuel Supply - Alfa Romeo Bulletin Board & Forums

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Old 12-28-2012, 08:08 AM
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Spica to Weber Conversion - Fuel Supply

I am converting my 74 Spider to Webers, euro intake manifold, filter box, along with significant headwork, cams and compression changes plus new Motronics.

What is the best way to handle the fuel delivery system? I would like to hear from others who have done this conversion on their Spica system and what worked best for them. I have Pat Bradens "Weber Carburetors" book and it describes the Shankle conversion kit and reuse of the Spica fuel delivery system.

Here is what I have now. I restored and upgraded these components just before taking the car down for painting and engine and other work.

Refurbished fuel tank from later S2 with internal pump.
New hard lines in trunk to route fuel over the exhaust pipe.
New inline filter and new primary fuel pump with modified supports behind differential.
New rubber fuel lines on supply and return.
Supply line from tank output to inlet side of fuel pump is 12mm, 1/2" diameter. The rest of the system is the metric equivalent of either 5/16 or 3/8, can't remember which.

The fuel delivery system, including the low pressure light worked well before I pulled the car off the road for painting and engine work.

I know the Spica pump system runs at 12-14 psi at 0.6 gal/ min and the pump does not like to be dead headed. I know the Webers like fuel delivered at about 3.5psi.

I like the idea of leaving the existing Spica front fuel filter in place along with the return lines but do not want to compromise the Weber performance or over stress the primary Spica Fuel pump.

I understand there are a couple options but not sure what others have done to overcome some of the issues.

I am told Carter pumps will fit in the Spica pump bracket and put out 4 psi.
I think they have components that will allow them to mate up with 1/2" inlet and 5/16" outlet. Their techincal service dept is out until Jan 2.
Have any BB'rs used this pump?
Did you leave the intank pump in the system?
Did you leave the Spica filter and return lines in place and simply use a tee connection to carb supply and return line?

Shankle's kit shown in Pat's book, utilized all of the Spica fuel supply components. It appears he provided a tee fitting to a regulator that fed the carbs and the other side connected to the return lines.
Has anyone implemented this system.

Another option may be to modify the Spica final filter housing to reduce the outlet pressure to 3.5 psi and leave the whole system in place. The low pressure light would have to be disconnected. I am not sure exactly what would need to be changed here and how. I am ok with doing this if it has worked well for others, not looking to experiment though.

I think that tuning the Weber carbs will be enough of a challenge all by itself. I would like to keep the fuel supply system simple and reliable.

I do intend to preserve the Spica components so nothing will be discarded.

Sorry about the long post, appreciate any insights.
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Old 12-28-2012, 08:37 AM
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When I bought my Spider in '99 the PO had installed the Shankle conversion utilizing the existing pump and a return line.It worked OK. I believe in keeping everything as simple as possible so when I rebuilt the engine with a Euro manifold I got rid of all of the SPICA stuff and installed a low pressure pump and I retained the pressure regulator that was part of the Shankle kit.
I have used the cheap, block type facet pumps, a Carter vane pump and now a Facet bendix type pump. I think that the Carter vane pump is the best but it is loud. The new facet pump takes forever to fill the Webers after the car has been idle for a few weeks and it appears to be sensitive to the level of fuel in the tank. I do not have an in-tank pump.
Gigem75 has posted that he has had good experiences with another Carter pump which may be a Bendix type.
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Old 12-28-2012, 09:07 AM
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Thanks Ed,
Gigem75 and I have been talking about this. He does not have an in tank pump and I think he has a gravity feed tank. I don't think he has a regulator.

After a few pm's, I thought it would be worth it to ask the question to the BB. Surely, someone has already done this, but maybe not.

We'll see who responds.

Thanks,
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Old 12-28-2012, 03:59 PM
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My 71 has the Shankle SPICA/Weber conversion kit. I recently replaced the fuel pump which ( I believe) came with the kit with a Facet Blue Top pump. It's mounted in the place where the original pump sat, and I retained the original gravity feed tank (although I did make a heat-shield for the fuel line where it passed close to the exhaust. Probably unnecessary since the car hadn't burned up in 40 years, but hey - it makes me feel better).

Since you mentioned that you're going with an in-tank pump this may not be useful to you, but here's a link to a post where I have some pictures of how I mounted it to the original pump mounts.
http://www.alfabb.com/bb/forums/spid...-mounting.html

Something you didn't mention that I do think will be of value to you is including a fuel pressure regulator in the fuel line. I have a Malpassi Filter King set to about 3.5 PSI. I know that Carter and others make fuel pressure regulators which are less expensive and I imagine that they're just as functional. Using a pressure regulator will reduce any concerns about the exact output pressure of your pump, in-tank or otherwise, something worth thinking about if you are going to keep the high pressure SPICA in-tank pump.

On a related note, in my referenced post I was chasing a lean-out bog at 5300 -5500 rpm under hard acceleration. I believe that I've tracked it down, although I have to wait for the weather to recover a little more before I can do much driving/testing. I had thought that it might be lack of fuel output from the rather small pump that I had. Now, I believe from some reading I've been doing that I may have my fuel pressure regulator actually set a little too low, so expect to do a little adjustment after installation.

I mention this to point out that you have too little fuel pressure as well as too much, so keep that point in your thinking as you adjust things.
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Old 12-28-2012, 04:50 PM
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Those little Facet pumps are pulse type and the pressure is constantly varying. I could never get the pressure high enough for high end performance without flooding at idle. The pressure regulator can only do so much.
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Old 12-28-2012, 07:04 PM
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Ed & Lokki,
Thanks for the responses. I appreciate the product references.

I am hoping that others will weigh in as well.

I think there are two approaches;
1. Dedicated system w/o Spica(+ or - in tank pump), vane pump with pressure regulator.

2. Partial Spica system with in tank pump + vane pump + tee connection to return line + pressure regulator between tee connection and carbs. In this system the front fuel canister type filter would remain in use. The in tank pump would make sure the vane pump is not starved during low tank levels and the pressure regulator plus return line would allow for excess and over pressurized fuel to return to the tank.

I am leaning towards trying to make 2 work as I like the idea of the front canister filter. The part I am not sure of is whether the return line is necessary. If it is, then the fuel pressure may never build up as there would be less resistance in the return line than in the pressure regulator to carb feed. I guess it would require a second pressure regulator in the return line set to say 4.5 psi to ensure the carbs are fed at 3.5 psi.

Or, eliminate the return all together, approach 1 and take the chance that the in tank pump will not burn up trying to push against 3.5 psi regulator. I am not convinced the vane pump can pull the fuel out of the top of the gas tank without assistance from the in tank pump.

I really do not want to put a fresh engine at risk with a lean running set up.

Maybe I am over thinking this, just don't want to screw it up.
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Old 12-28-2012, 07:06 PM
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Ed - are you talking about the pump I had, or the pump I have now? If the pump I have now, whose pump do you use? I haven't had any trouble at idle, and I believe I've worked out the stumble @ 5500... One of the things that the Malpassi does is damp pump pulses.

Gary - Can't be of much help on the return-line question other than, my car doesn't have one. No T and no return line traveling back to the tank.

It would seem to me that the question to ponder is this: how much flow comes from the in-tank pump and how much pressure can the intake of the main pump handle?

I would believe that if the output of the low pressure pump is 3.5 PSI, it's 3.5 PSI no matter what pressure feeds into it. I would also believe that the in tank pump's function would to be to prime the main pump rather than pressure feed it. The siphon and suction effects should pull fuel from the tank into the main pump once it's started.

I'd agree on the concern about running lean on a new engine. Much safer to start rich and lean out from there. Set the pressure regulator to 4 or 4.5 psi and lean out later.
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Old 12-28-2012, 07:32 PM
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I was referring to the square pump that makes a distinctive pulsing sound and costs about $30.

This Carter vane pump has great fuel delivery and it does not need an in-tank pump.As I posted earlier, I like to keep it simple. One pump, one fuel line, one regulator.
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Old 12-28-2012, 09:25 PM
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The tank I have installed only has one way to deliver fuel and that is through the gauge and in tank fuel assembly. There are no hard lines in the tank that protrude to the bottom to allow fuel to be picked up. If I abandon the in take pump, I will need to weld a tube extension onto the fuel gauge assembly.

I would like to keep it simple and will have to solve the pick up tube issue as well as the diameter change from 1/2" to the 5/16" on the vane pump. May be able to find some reducers that can go from 1/2 to 5/16 and be brazed onto the gauge assembly.
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Old 12-29-2012, 06:25 AM
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Using the original electric pump to feed carbs is actually very simple; since the pump is very reliable I've used this more than once.

Your 1974 does not have and does not need a priming pump as the low pick up point on the Spica fuel tank prevents starving efficiently. I believe the priming pump used on later Spiders resulted from a different arrangement.

You need to:
1- Remove the banjo bolt that holds the double ended return fittings;
2- Gut the innards of the banjo bolt which was actually a pressure regulator;
3- Refit the bolt and fitting blocking the carb side.

The return line now has very little flow resistance and the carb float bowl valves are sufficient to control fuel input. A pressure regulator is an added safety to prevent overflow and adjacent disaster.
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Old 12-29-2012, 07:28 AM
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Ditto Ed's suggestion for keeping things simple and using one pump. The in tank pump and/or the stepped hose on the sender assembly will, of course, eventually fail. That complicates matters as the stepped hose is difficult to source and expensive when it is available. You could proceed though, using the parts you have and later change to a sender assembly that does not include the pump ($70). Also, does anyone know the volume and pressure specs of the in tank pump? Maybe you can just use the in tank pump alone. In addition to 3-4 psi, you need a volume of around 20 gph for Webers, I think (please double check the volume spec).

I suggest using a FRB-11 filter/regulator or similar as used on the carbureted 101/105 cars. I can't think of a good reason to keep the Spica filter unless you just want to. No return line is required. HTH.
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Old 12-29-2012, 09:03 AM
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Rich,
I am in favor of keeping it simple. I think the best way to do this is to replace the in tank pump assembly with one that does not include the pump and then use a vane pump with regulator, no return or Spica filter.

For me the only missing information is the in tank assembly sans the pump. You mention $70 which is fine by me but I would like to know where to source this. IAP has fuel tank sending units but they do not include any piping for fuel to exit the tank. The ones they show are for a later model Bosch units I think. The units is this picture were refurbished before I installed them in the tank.

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The tank I refurbished for the 74 was from a later model (Bosch?) that had a pickup tube that extended all the way down to the sump in the tank (No in tank pump). The service bulletin for these included adding an in tank pump assembly by cutting off the portion of the tube that interfered with the sending unit and pump. I of course did that. I could have used the tank for my Weber conversion. Unfortunately, it is too late as I modified it already for the Spica.Name:  Outlet mod for internal Pump.jpg
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So, do I need to source a tank from a later Bosch car that has the separate pick up tube that extends to the tank sump?

I suppose I could take the tank to the radiator shop and have them remove the existing partial hard line and reinstall a new hard line to the sump. I think this could be done without opening the entire tank.

If I stayed with the in tank set up, it looks like a fitting on the vane pump would allow for the 1/2" line. I could then abandon the Spica front fuel filter and return line and replace with a pressure regulator. I have extra step hoses. Would still need to check on deadheading of in tank pump and affect on vane pump.

I thought this would be easy.
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Old 12-29-2012, 09:33 AM
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Yves,
The OEM tank in my 74 was rusted out so I refurbished a later model tank that did not include a discharge on the bottom of the tank. The fix included a new in tank pump and fuel tank sending unit assembly.

Also, the PO's have pretty much gone over the Spica stuff so I don't know what is 74 stock and what has been replaced. The fittings on the Spica pump are barbs, except for one.
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I have a couple of donor Spica Fuel Filter canisters and they are all different from each other. See Photos.

If the banjo bolt you are referring to is on top of the filter canister, I do have one unit that includes this fitting.
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This assembly would seem to be more complicated than a vane pump and regulator and I would still need to resolve the in tank pump potential dehead issue.

Wish now that I would not have modified the later style tank.
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Old 12-29-2012, 01:59 PM
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To my knowledge, it is permissible to deadhead the in-tank boost pump (but NOT the Spica main supply pump!). The in-tank boost pump is pressure limited to 3-3.5 psi.

I'm not familiar with carb conversions, not having done one myself, however I would think that the in-tank pump would have plenty of capacity to fill the fuel bowls on Webers. So, I think I'd keep the modified tank (it was an Alfa Service Bulletin in 1982), keep the in-tank boost pump, keep the rear in-line fuel filter, and remove and bypass the front Spica fuel filter altogether.

And don't dare throw any of the Spica parts away!
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Old 12-29-2012, 02:15 PM
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Thanks John.
I have an email into Airtex tech support about deadheading their 8778 in tank pump.

I am leaning towards adding a vane pump and regulator and eliminating the main Spica pump, front Spica canister filter and return line. The rest of the system would remain as it is. Pending of course the Airtex tech comments.

This would give me the: in tank pump, in line filter, Carter Vane pump, fuel regulator and carbs in that order of flow. No return line.

The other option is to modify the pressure relief valve on top of the Spica filter canister from the 18 psi limit down to 4 psi, add a tee between the supply and return with a pressure regulator and feed to the carbs and leave the entire Spica set up in place. I am not sure how to modify the pressure relief valve to accomplish this though. I am not interested in trial and error to dial this fix in.

I promise to not dispose of any Spica parts and will probably send you some of my extras once things get settled.
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