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Discussion Starter · #1 ·
I have a 1980 Spider with 2 Solex carburetors.
After some major repairs, the car is now backfiring like crazy
when I take my foot off the accelerator which it didn't do when I bought
it at the end of last summer.
I haven't had a chance to talk to the shop about this yet, and I will,
but just wondering if anyone out there has some words of wisdom,
other than, "just live with it," as it now actually sounds like the "heap" that
it is. I was told that their "carburetor guy" had synced the carbs, but other than
that, he says there are no further adjustments he can make. I'm beginning to
think it's time to find a new shop.
 

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Definitely don’t live with it. What all did the shop do or get done since it last ran well.
 

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Backfiring on the over run is a combination of air leaks in the exhaust and poor closed throttle mixture settings. Either too lean or too rich the mixture does not ignite in the cylinder but it ignites in the exhaust system. I don't know Solex but with Webers having the idle screw in too far and the idle mixture screws out of whack will cause back fires.
 

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Discussion Starter · #4 ·
Backfiring on the over run is a combination of air leaks in the exhaust and poor closed throttle mixture settings. Either too lean or too rich the mixture does not ignite in the cylinder but it ignites in the exhaust system. I don't know Solex but with Webers having the idle screw in too far and the idle mixture screws out of whack will cause back fires.
Yes, thank you...even I, with little knowledge of how car engines operate, suspected that it had something
to do with the the the "mixture" without actually ever working on a carburetor and find it hard to believe there is no way to adjust it. Why change out from the fuel injection to put on inferior carbs?
 

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Eh, the 1980 spica system was pretty constrained. If it was all original today you would have a hard time even finding an air filter for it.
 

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Discussion Starter · #6 ·
Definitely don’t live with it. What all did the shop do or get done since it last ran well.
They did a lot, but not engine work. Radiator leaks, differential leaks, U-joints, transmission fluid leaking, replacing seals, it's amazing it even ran, but as those old spiders go, this one was way better than most and they are beautiful little cars.
 

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Discussion Starter · #7 ·
Eh, the 1980 spica system was pretty constrained. If it was all original today you would have a hard time even finding an air filter for it.
OK, but would it perform better? I know a lot of people say the spica is great when it's functioning correctly, but that they can be very finicky? Also, would there still be backfiring issues with spica/fuel injection?
 

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Sure, the spica would run better than you currently are, there are a couple things with spica where it could backfire, well popping on decel. Your current carbs will run better too once sorted out. Maybe you have an old school Brit place in your neck of the woods that knows Solex well.
 

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Discussion Starter · #9 ·
Sure, the spica would run better than you currently are, there are a couple things with spica where it could backfire, well popping on decel. Your current carbs will run better too once sorted out. Maybe you have an old school Brit place in your neck of the woods that knows Solex well.
Thanks good to know!
 

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Solex were not the best carburetors that Alfa used but they were cheaper than Webers. The 80 and 81 spiders had the worst performance of the SPICA era and were prime candidates for Carburetor conversion. Buy an infra red thermometer and point the spot all over the joints in the exhaust system when the engine is running and look for hot spots which indicate leaks. I cannot tell you how to adjust Solex but if they were Webers I would try backing out the idle speed screw to get the lowest sustainable idle rpm then slowly adjust each one of the idle mixture screws in and out to try to increase the rpm. If you find a max rpm position for them then back out the idle speed screw some more and repeat until you get no further improvement. You must do this with the engine hot. If the carbs have bypass air screws then they should all be completely closed.
 

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I have a 1980 that was converted to Webers by the previous owner and from all I can read, the performance of the 80-81 is dramatically better than the original setup because in an effort to meet the new emissions standards they pretty much crippled the Spica system. You're better off with the carbs even if they aren't optimally tuned yet.
 

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Discussion Starter · #13 ·
Yes, I think you are correct, but from what I've read the Solex carbs are the worst of the 4 types of carbs that were available, so that's also part of the problem. But it is some consolation. How are your Webers, they seem to be the carbs of choice, do you get a lot of "popping" when not accelerating?
 

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They are great now that I have them jetted properly. They were taken off a 65 Gulia Super and put right on the Spider without changing anything, so they were setup for a 1.6L engine. The Spider has a 2L so once I set them up properly, the car runs just great. The only slight popping I get is when slowing myself with the engine at high rpms.
 
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