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Discussion Starter #1
SOLEX CARB CONVERSION

i am swapping the bosch injection system on my 1986 US imported series 3 spider, for a pair of solex carbs that i have had laying around. i am hoping that some of you can help me along the way.
The injection system has 2 fuel pumps, one in the tank and one under the car by the fuel filter. can i still use these or will the pressure be to much. i know the one in the tank is low pressure and the other one is high..
As the injection has an ECU, can i by pass it and remove some of the wireing or should i just tape up the wires i dont need.
does anyone on here have the solex carbs on there spider, if there is can you take some photo's of them and how there set up.

this photo below is what i have, what else do i need. i know i need the top part of the airbox housing. so if anyone has any parts for sale please PM me.

many thanks Martin
 

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I'm no expert on this specific subject. But '86 4 cyl Alfas in the USA ran Bosch Jetronic injection and normal ignition, if I not mistaken, and cat and air pump. On such instalations the ECU only managed to injection, not the ignition. So you remove all injection part incl. high pressure fuel pump, the cat and air pump (subtitude with std. euro exhaust manifold and front pipe/silencer). Also you need the carb models coolant pipe and termostat housing and the std. carb adapters.
You seems to have the lower airfilter box, but you need the top and filter and the bracket that holds the air filter housing.
I would buy rebuild kits for the carbs and make sure that the jets all are specific for the 2 Ltr Nord engine from the 80's (Alfa 75 or equal). Thr Solexs are the less popular of the 3 std. fits, others are Webers and Dell'Orto., but I think they ar all right, just a bit different.
Good luck
Erik
 

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Is there something amiss with the L-Jet that can't be sorted? Why the conversion?

The in-tank pump MAY be sufficient to work alone but a fuel pressure regulator will need to be installed no matter how you slice it.
There are injector cutouts in the L-Jet head that carbed cars do not have but I don't think it would be an issue for a street car. Race engine is a different matter as the airflow may not be optimal.
Yes, you can just unplug the fuel ECU and leave all the wiring if you wish. However, this means that the variator will no longer function which will mandate a change to the cam timing if you want the thing to run anywhere near decent. The FI harness though is an add-on meaning that it can be removed from car without cutting anything.
The ignition system is a Bosch Motronic (digital) with it's own ECU located behind the right rear trim panel. This system also includes a vacuum (load) sensor that is fed by a 'common' vacuum port on the L-Jet intake manifold. A carb manifold does not have a common port (only a single cylinder port) so something would have to be fabricated in order that the sensor receives a proper vacuum signal. The car will run without this sensor BUT the ECU will think that the engine is under full load all the time and will retard the ignition timing. Performance, mileage and emissions will suffer. An option here would be an aftermarket ignition system or a points/non-digital Alfa dizzy.
If you're doing this conversion for more power, then you'll need better cams. You'll also have to lose that pathetic exhaust manifold. S1, S2 & S4 manifolds flow MUCH better and are a direct bolt-in but a different front pipe will be required.
Sounds like you could use some color wiring diagrams. If you'd like one, please send me your email address in a private message and I'll send it to you.
 

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Discussion Starter #4
i am having a running problem. i have not used the car for about 2 years now as it broke down. the fualt was it blow the fuse for the fuel pump, with one thing and another the car was put away, i then did some work on it last september, but means of putting a switch in to turn the fuel pump on but the problem was still there. so i put it away again untill last week. i have now put the fuel pump wireing back to how it was and replaced the fuel pump and fuel filter, along with the dizzy cap and rotar. the fuse is not blowing now but i am having poor running.

here is a youtube link to hear it running. the worst bit is about 25 seconds in.

YouTube - Spider engine running poorly.mp4
 

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It's hard to tell from the vid (crap speakers on this laptop) but it almost sounds like there's a dead miss in the engine (not running on all cylinders). Are the plugs and leads in good order?
Not saying for sure that it's a dead miss but an easy way to determine which cylinder(s) is not firing is to the start the engine from cold, let it idle for a few seconds then touch each cylinders exhaust pipe with the back of your hand. A pipe that's cold (as compared to the others) means that cylinder is not firing.
 
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I can't tell from the sound either. Try draining the fuel and putting some fresh fuel in. If you've left unleaded in the tank for 2 years it's not going to be very good now. Also change the fuel filters. I really wouldn't bother with the Solex's.
 

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Discussion Starter #7
not going to use the solex carbs now. keeping it injection. i rebuilt a spare engine in 2008 so i think i might as well fit it and give the old engine a rebuild this year to. from what i have found its more than likely the coil that is braking down under load. well i have 4 months or so to sort it and get in back on the road for the summer.
 

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I always wonder why-if carbs can (as some say!) be swopped for the injection system-why have Alfa designed the piston completely different for the injection models? My S4 Motronic pistons have a squared off top, not domed.
There must be a reason...or are they just saving metal!!:lol:
See middle piston of following illustration. (Left is normal 2 litre, middle is Motronic injection piston and right is high compression 2.0 litre)
 

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I don't know how the JetTronic pistons look, but the S4 piston may have got the different shape due to pollutions laws. They were tighted around 1990 in many European contries then, cats being introduced and so on.
Erik
 

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I always wonder why-if carbs can (as some say!) be swopped for the injection system-why have Alfa designed the piston completely different for the injection models? My S4 Motronic pistons have a squared off top, not domed.
There must be a reason...or are they just saving metal!!:lol:
It (the Motronic piston) is a more modern design and gives a better combustion chamber shape, which with hindsight is one of the failings of the Nord. It also gives a higher compression ratio than the domed pistons fitted as standard to carbed cars, 10:1 vs. 9:1. It's the piston of choice for building more powerful versions of the engine, without going to the expense of forged/custom pistons - the Borgo on the right has a still higher c/r, 10.4:1, but is an older design.
 
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