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I am working on a 1978 Spider Veloce (have not yet got the car running yet), in any event I am working my way through the ignition system. I am planning on changing the points (among other things), both sets. The distributor is a Marelli with the centrifugal mechanism ABOVE the breakers. I cannot determine how the centrifugal mechanism is removed so I can get to the points?? My manuals don’t seem to provide this information? Can anyone give me a hint? Thank You in advance.
 

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You dont need to remove it to get to the points. Just "expand" the mechanism to get to the screws. FYI I had a hellofa time with my Marelli, as it was oviously faulty and the cause of misfires and no-spark situations.... Switched out another distributor, and all was well. Good luck! P.S. Mark the location of the distributor and the direction the rotor points, and REMOVE the unit. It will be almost impossible to do it in the car.
 

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If You Can, Get a Bosch Distributor!

I had a Marelliplex with my Duetto that had an engine change by the PO. It worked great until it didn't work, and then, no matter what I replaced, it didn't work. I finally put in the Bosch single point distributor I had from my other Duetto, and it started right up. Not sure what was wrong with the Marelliplex, but it was beyond me. I never did figure out how to replace the points (even thought I didn't have any as I found out later)! Bosch distributors have the advance mechanism where God intended, below the points, so they are easy to change.
 

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I dont mean to change the focus of this thread, but can you interchange a Bosch Dizzy for a Marelli with no modification??? I want to get a hotspark electronic ignition module to alleviate the fickle spark on my 77, but it will not work with the marelli system. If the Bosch will be a no-brainer drop in, I might be searching ebay for a substitute..... Thanks to anyone with the answer/recommendations.
Peter

Still driving in November... One good thing about global warming.... No snow yet! :)
 

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I Replaced my Marelliplex with a Bosch without any Problems.

As I said in my original post, by obviously 1991+ engine in my 1967 Duetto started just fine when I replaced it with my 1967 Duetto with the apparent original Bosch distributor. So I think you could go backward and have a functioning ignition system.
 

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The advance curves are different for the 1600, 1750 and the 2 liter engines. Using an earlier (1600) distributor in a late engine will give either too much advance at high RPM if set at the F mark, or will be retarded at idle/slow speed if set at the M mark (preferred method).

The Bosch advance curves can be changed, but should be done on a distributor machine.

I belive that Pertronix is now making a module to replace the points in a late Marelli weights-up distributor. Give them a call. Be sure to take the distributor apart to clean and lube the inner shaft, they get sticky and binds up the advance mechanism.
 

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I have ordered a new distributor from IAP that has a large set of electronic advance curves for various Bosch and Marelli distributors. It costs about $400. It includes a trigger module and it hooks up directly to a coil.
I am running a Shankle Sport Marelliplex that makes good strong sparks but the initial curve is too steep. This causes erratic idle and occasional pre-ignition at around 3500 rpm.
Is there a "best" curve for a 2L engine, 10:1 pistons, CB47 cams and 34 mm venturis in the Webers? I will be swapping out the intake cam for a 12 mm that I bought from Alfar7 and I will also be swapping 36 mm venturis into the Webers. I figure that at least one of the canned curves should work for me but it would be nice to avoid a lot of trial and error.

Thanks,
Ed Prytherch
 

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The best curves I have come up with for a 2 ltr engine with your combination are:

12 1/2 to 13 degrees in the distributor, or 25/26* at the crank, with full advance around 3/3500 rpm, and timing set at the M mark at full advance, (3500 rpm). This gives 9 or so degrees initial which the cam timing you are using likes.

Do you know what the 12mm cam is or the duration at .050" lift? It may make a difference on the best lash setting for your combination for all around performance.

Unless this is a strictly a race car, you will get better low end with the 33mm chokes with little horsepower loss above 6000 rpm. If this is a 7500 rpm engine then go with the 36mm chokes.

More is not always better :).
 

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Keep it simple, a Marelliplex and Marelli stock distributor on a 78 are two differnt animals. The Plex was stock only 80-81, it is a nice electronic unit and has no points. There were various models of the stock Marelli distributor with points, they'll all seem to work just fine. To change the points on a Marelli, rotate the engine to TDC, make sure both intake and exhaust valve are closed, make sure the ignition rotor is just or about the number sparks plug wire on the cap (I dot tag my ignition wire with a paint marker). Now make sure the car is out of gear and do not move the engine, make a drawing noting the direction of the ignition rotor fo reference. Remove the distributor and change the points and condense on the bench, you don't have to remove or alter the advance mechanism and would strongly advise not messing with it. You'll notice that by simply turning the distributor you get access to the mounting screws. Reinstall the distributor, it should fit in the drive only one way and the ignition rotor fits on the advance mechanism only one way.

PS a crows-foot 10mm distributor wrench is an important tool for this job and adjusting the timing
 

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Hi George:
Thanks for the reply.

The duration of the new cam is 266 @ .050, or 292 @ .014. Max lift is 12.35 mm. I will be retaining the CB47 on the exhaust.

I had some discussions about venturi sizes a while ago and I think that both Jim Niel and Gary Williams said that they found 36's fine for road use.

Ed
 

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I know the Marelli Distributor, when set up correctly, is a good solid unit, but obviously a newfangled electronic trigger has just got to be better if designed as it should be. I will check out the Petronics unit and maybe during the winter give my Spider a well deserved power boost, if not a predictable spark that doesnt break up from time to time...
 

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Keep it simple, a Marelliplex and Marelli stock distributor on a 78 are two differnt animals. The Plex was stock only 80-81,...
To pick a nit, the single pickup Plex was never fitted to US market cars from the factory. Pasted below is a brief distributor application post I wrote earlier this year;

The skinny on the MarelliPlex (Marelli dizzy SM804AX) is that it was never fitted to a US version Alfa from the factory. It was (is) available only as an aftermarket.
Starting with the 69 model year, Alfa fitted the Marelli S103B single point dizzy to the 1750s. With the introduction of the 2000 in 1972, either the S103B or S103BA were fitted through the 1976 model year. For the 1977-1979 model years, a Marelli S166B dual point was used. For the 1980 & 1981 Monofarfalla Spica years, Alfa fitted a Marelli SM809AX dual pickup electronic dizzy.
The cap you need jjb is Centerline #IC891. This cap fits both the SM804AX and SM809AX dizzys.

I had some discussions about venturi sizes a while ago and I think that both Jim Niel and Gary Williams said that they found 36's fine for road use.
Don't think that was me, Ed. I've not driven a street Alfa with 36mm vents. I have extensive seat time with 34s though and think them perfect for a mild street engine. George is absolutely correct here; large vents improve high end airflow at the expense of low-mid range drivability.
 

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Hi Jim:
My memory let me down again. But you did post this in a thread with John M:

>Let me take a moment to share what I know and learned (which isn't much) about Weber DCOE jetting which will explain why I think a 155 air corrector is WAY to small.
First up is the size of the engine and the RPM at which peak power is produced. This will determine the venturi size. Luckily, someone's already figured all this out. Assuming peak power at 6000 rpm and one venturi per cylinder, a 2000cc engine needs a 36mm venturi, 1750 - 32mm, 1600 - 30mm and a 1300 gets a 27 or 28mm. <

I took that to mean that you endorsed 36mm for a tuned road engine.

I should probably change out the camshaft first, then the venturis later so that I can tell what effect each has.

Back to the distributor curves. The IAP distributor includes the 0 231 178 006 which Jim Kartamalakis has recommended in one of his posts.
It also offers "006 tuning - for high compression, hot cams. Static timing 12 deg; max advance 34 degrees." That implies a range of only 24 degrees which sounds very short. Maybe "high compression" means a lot more than 10:1.

Ed
 

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timing curve

Ed, might I suggest starting with a mild curve initially, as with the cam change you will have a bit more cyl pressure than with the slower ramp C&B cams as their overlap bleeds off some of the early fuel charge. Tune with a blend of 50% Premium & mid-grade. Once all is tuned for best cam timing & jetting then spark advance curve you can go to premium with a better reserve against preignition. Doing this in the winter you might just use 25% Premium then reajust as above in the first 90 degree days.
I would think with 45 DCOEs jetting at 140/180 in F16 tubes, idle 50-55 f8/f11. Use as lean an idle jet as does not leave a flat spot in transition. Keep your 34 choke tubes as I think you will likely go back there.
 

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The advance curve I suggested will work on a 2 ltr with either cam profile since a cam with less degrees of duration can use the timing as the torque will be lower in the rpm range, and a cam that builds up a higher cylinder pressure will be higher in the rpm range (ie: above 35-4000 rpm) and the advance is all in, and is not a factor.
 

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Aah! I see what you mean, Ed. The venturi sizes listed are derived, in part, from here. There's also a good explanation relating large and small venturis. This explanation, IMO, is why Alfa chose 32mm vents for the 1750 and 2l engines.
 

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Hi Jim:
My engine is running really well with 34's and CB47 cams. It will idle at 700 rpm. Pick up is good in the lower gears and I can get away gently from a little over 2000 rpm in 5th. So it feels like it could take bigger venturis. But I will change the dizzy first, then the cams and finally the venturis. I can always put the 34's back if I have driveability problems.
Ed
 

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Just Got Back to This Thread

The 1600 in the Duetto that I recently purchased that had a Marelliplex ignition. I have the engine S/N someplace, but not available at the moment. It supposedly is from an 1980-81 Alfa. The valve cover is "krinkle black" with a red Alfa Romeo logo. As I said before, I just replaced it with Bosch single point distributor and have not had any problems with starting or driving.

Based upon Papajam's post, this engine should not exist, at least in the US. I purchased the car from a PO in CA, so I would assume that the replacement engine came from a US car, but I may be wrong.

Any insights you may have would be appreciated.
 
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