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Discussion Starter · #1 ·
Hi All,

I am at my whits end on this 1974 Spider, Model 2000. I have recenlty converted it to dual Solex Carbs with a European style manifold. I will list out everything I have replaced and tried but I cannot get her to run at an idle and can only get her to run with very little power by pushing her to rev high and when she does she backfires out the carb barrels. She sounds like a 21 gun salute of muskets.

*Fuel Lines
* Fuel Filter
*Drained and replaced Fuel
*Fuel Pump
*Fuel Pressure Regulator (set to 2.5 psi)
*Coil
*Ignition Module
*Wires
*Plugs
*Cap
*Rotor
*Checked timing according to other forum posts
*Checked Cam Lobes at cyl #1 Comp
*Checked Timing marks at cyl #1 compression
*Checked rotor position at cyl #1 comp
*Replaced Intake Manifold - European style
*Replaced SPICA with Solex Carbs - rebuilt (SPICA pump is still in place)
*Checked Float level
*Checked Bowls
*Checked needles
*Carbs squirt nice spray of gas on throttle
*New gasket on Manifold
*Taken off and put on manifold and carbs multiple times

I am sure I forgot something. As you can see I chased down an ignition problem, a timing problem, a vacuum leak, gas issue, etc.

I am stumped. I appreciate any sage words of advice. I can try to post a video if anyone thinks that will help.
 

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Are you backfiring during acceleration or deceleration? Have you checked the exhaust system for leaks?

You didn't mention if you have synchronized the carbs and tuned them for best idle operation. This has been covered extensively and you can search previous threads. The Autobooks manual also has a good description of the process.
 

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If it occurs on acceleration my first thought would be a timing issue. but you say that both valve and ignition timing, and the ignition components are good. How about the mechanical advance on the distributor? Can you see it working with a timing light?

If all of the above are OK then I would check the carb synchronization. I am not familiar with the Solex jetting, but have you checked that it is correct for a 2.0L engine?
 

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Did you confirm the firing order? With four ignition wires it's easy to mix two of them up. Make sure you are setting the order in the correct distributor rotation direction, also. It's easy to think the order is correct, but you are looking at the rotor as turning one direction when it is in fact turning the other. All these things learned the hard way over the years.
 

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Unplug the brake vacumn booster from the mainifold and and plug the manifold inlet port to see if anything changes--check for intake leaks with wd-40 or some other spray--
 

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I am with intune on this I would check your plug wires , did you change your cam timing at all. I have allso done this, wires on wrong and bang. smoke and fire comes out of the carbs.
 

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Discussion Starter · #8 ·
I will check again as I would really love it to be that "simple" but I have checked the wire to fire order 1-3-4-2 and even checked the rotor at every cyl compression to make sure each and every one was hitting in the right order. But even before I did that I actually charted out every possible combination of wires and tried each combination.
I did not change the cam timing as it was set perfect when I took the cam cover off.
 

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Where are you located? Maybe a fresh set of eyes could help. Sometimes you get so far into it that you start to see what you expect.
 

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I had a similar problem of popping or spitting out through the webers on my car. This was fairly constant especially between 3000 and 3800 RPM on partial throttle in third or 4th gear. Turned out to be the idle jets were too lean, went up one size and adjusted the timing (probably about the 4th go round) and the problem was solved. You mentioned that you were down on power even at higher rpm's, I did not have that problem.
 

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Discussion Starter · #12 ·
Update

Following Intune's suggestion I checked for spark at each plug with a timing light. Interestingly enough there is spark at Cylinder 1 and 2 but not at 3 and 4, consistently.

Relevant here is the car was switched to a Mirelli Electronic ignition at some point.

I have replaced the ignition module with a new one from Autozone. No Change. Today I will replace the ignition pickup in the dist with a new one from IAP. If this fails I am thinking of getting a new Dist from IAP that is a point Dist and chucking the electronic. Hoping simpler is better.

Thoughts?

Also, *BIG* thanks to Intune for taking the time to visit my Alfa and check it personally. Great Guy!
 

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Following Intune's suggestion I checked for spark at each plug with a timing light. Interestingly enough there is spark at Cylinder 1 and 2 but not at 3 and 4, consistently.
Gee, from your symptoms it has to be something downstream from the electronics and the coil. Like the cap, wires, or plugs. I would just replace all of these (plus the rotor while you in there) if their age is unknown.

It sounds like you have the factory Marelliplex electronic ignition - they take a different cap than the Marelli points-style distributors. But, Centerline and IAP should carry them.

Installing a new distributor with your old wires & plugs might not fix anything.
 

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Discussion Starter · #15 · (Edited)
Thanks for the reply Alfajay. I have already replaced all and had discovered the difference in caps. The points has a clamp down cap where the electronic has a screw down cap.

All 4 cyclinders passed the compression test.

The new Pickup did not change anything.

I have replaced everything from the coil to the dist and from the rotor to the cyclinder. The guys at IAP are helpfull but no one is confident that a new dist will solve the issue.
 

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If you are getting good fire on 1 and 2 , I would check my rotor cap , even a new one can have a problem. Look for a hair line crack , maybe a scratch , around 3 and 4 inside .((I maybe wrong but I dont think so) . If you have done all you can to show that 1 and 2 fire ok. than the pick up will be fine. )) At lower rpms the crack or scratch might not be a problem, But with higher rpms this can cause the spark to walk down the crack, because of the path of least resistance. allso 3 and 4 are on one carb maybe this carb is way to rich. when a plug gets wet it is harder to fire, On mine when i had a problem with the car it would not take long for thr plugs to file out maybe two stop light, you might think you got them cleared out with a little rev, but down the road they start poping. Just thinking out loud. hope you get it running soon.
 

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IMHO there is only one reason an engine "backfires", i.e. fires thru the exhaust valve, and that is due to the timing being misadjusted and firing late in the cycle after the exhaust valve is open(ing).
 
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