Alfa Romeo Forums banner

1 - 12 of 12 Posts

·
Registered
Joined
·
115 Posts
Discussion Starter #1
I've got an intermittent and annoying problem with my 74 spider. When accelerating and rpms around 4000 I my engine jerks and seems to miss and sputter. Fuel filters are new and the low pressure light doesn't come on when this happens so I'm tentatively ruling out fuel feed as a cause. I've got a Pertronix electronic ignition module giving spark. Is it likely that my distributor advance is not working sometimes and this is what's causing it? Not sure how to verify and what else to consider so I thought I'd ask the Alfa braintrust.
Thanks,
Chris
 

·
Registered
78 Alfa Spider
Joined
·
94 Posts
Hey Chris,
I'm curious to hear what others recommend, as I'm having the same issue with the same setup as you.
 

·
Registered
Joined
·
77 Posts
Check fuel level in carburators. If level in carburetors bowl is too low may occur fuel starvation. Depending on the brand of your carbs different level of floating chamber apply.
 

·
Registered
Joined
·
115 Posts
Discussion Starter #4
I forgot to mention that it's a Spica equipped engine so no carburetors and the tank is clean and full. I keep thinking about the advance mechanism in my distributor but don't know how to verify if it's properly working.
 

·
Registered
Joined
·
1,271 Posts
Can you provide some additional background? Did the problem appear suddenly? Concurrently with the Pertronix install? Are you using the stock Marelli distributor and coil, presumably with a ballast resistor? You say the problem is intermittent. Does this mean there are times when the engine will rev to 6000 rpm or so without any issues?
 

·
Registered
Joined
·
77 Posts
I forgot to mention that it's a Spica equipped engine so no carburetors and the tank is clean and full. I keep thinking about the advance mechanism in my distributor but don't know how to verify if it's properly working.
Using a timing light you can check if idle advance and maximum advance are maintained as per the marks on the pulley according to RPM.
 

·
Registered
Joined
·
115 Posts
Discussion Starter #7
Can you provide some additional background? Did the problem appear suddenly? Concurrently with the Pertronix install? Are you using the stock Marelli distributor and coil, presumably with a ballast resistor? You say the problem is intermittent. Does this mean there are times when the engine will rev to 6000 rpm or so without any issues?

Sorry for the lack of details. It's a stock Marelli distributor but an aftermarket coil (Flame-Thrower is the label) with ballast resistor. It was installed this way when I got the car but I only drove it a couple of times before I tore the car down to restore it. Maybe that's a mismatch of coil-Distributor-Ignition or maybe the coil is losing it's snuff? I'm more of a mechanical guy and limited electrical knowledge. It doesn't exhibit the problem every time I rev it to 4K or beyond but more often than not.
 

·
Registered
Joined
·
1,271 Posts
I would begin by looking at the ignition basics, plugs, wires, cap, and rotor. Do a visual inspection and if indoubt, consider replacing parts. Plugs and wires would be first on my list unless they have been charged recently.

I don't think a problem with your advance mechanism will cause misfires and stumbling. You can remove the distributor cap and turn the rotor by hand to confirm the advance is free to move.

There are different Pertronix ignitors available that have different coil impedance requirements. You'll need to do some research on the Pertronix website to confirm what impedance is required for your particular module. If your coil and ballast resistor provide three ohms of resistance then you will not likely damage anything. Even if you have a mismatch, I can't imagine how it could cause a misfire. In my experience, when Pertronix units fail, they fail completely. You may wish to do some research to determine if there are other failure modes.
 

·
Registered
Joined
·
317 Posts
I had a similar problem to this but after changing from NGK B7ES to B6ES the problem disappeared.
 
  • Like
Reactions: Aris64

·
Richard Jemison
Joined
·
7,593 Posts
I suspect it has nothing to do with ignition, but an over rich fueling mixture at 4000-5000 RPM.

The only way to know mixtures is with a wide-band O2 meter.
 

·
Premium Member
Joined
·
960 Posts
Will the " cut the engine at speed, coast in and look at the plugs" be a method that may work in this case? Cost = free
 
1 - 12 of 12 Posts
Top