Problem tuning up a 1970T

[steve911T]

Been having an ongoing problem. Actually for several years. Problem is when trying to adjust carbs, usually have several unresponsive cylinders. When removing the plug wires from the plug, idle does not drop which seems to mean it is not firing. Car stumbles a bit on acceleration but kicks in all pistons. Car has been seen at a primo Porsche shop in Baltimore and they did not seem to know what was wrong. Engine was rebuilt 800 miles ago and was hoping we would find something wrong with the motor, but motor was fine. So, this seems to be an ignition problem. The car has new wires, new plugs, new distributor cap, new rotor, rebuilt distributor and rebuilt carbs. I am eliminating the Permatune and the coil thinking that if they were going bad, nothing would fire. I have an extra permatune and coil for swapping out if need be. I believe that it is the distributor. I will pop the old Marelli back in to see if it fixes the problem. The most obvious symptom is when the engine is running, any gear, except 1st, the car shakes between 23-2800 rpm under acceleration, kind of like the clutch is slipping which I think it is. Power is down, running about 80% of power.
Any ideas? Timing and dwell are fine. Steve

[Avanti]

If a Permatune is a brand of electronic ignition, I have seen some units drop individual cylinders causing a problem like yours. Your power balance test of removing plug wires is a good one but also connect a timing light spark plug wire pick up on each plug wire and see if the light flashes the same with each wire. This "poor mans scope" shows visually
intermittent cylinder firing from an ignition standpoint. Revving the engine sometimes makes a wire show activity when it didn't at idle. BTW, don't overlook the plug wires. How old are they?

[steve911T]

Wires are new!

[lrodri64]

Zenith?
I had the idle circuit completly plugged with old gasoline converted to varnish.
On two cylinders.
Also verify the firing order. Cables wrong installed
Also, the valve adjustment , too tight. No clearance.
All those things happened to me !!!!

[lrodri64]

Points or pertronix?
Try another dizzie!!

[lrodri64]

Don't use the small square fuel pump.
No fuel volume at all.

[steve911T]

Webers, permatune, points,and valves done by professional. Steve

[steve911T]

Yea, dizzie will be replaced next week to see if that is the problem. Steve

[1QuickS]

Sounds like a lean idle issue or lean transition.

Fuel gallery for idle jet is probably blocked so fuel isn't available for idle and progression for the offending circuit. Once on the mains then fuel is supplied by another circuit.

Follow the procedure "Clearing "Hidden" Fuel Gallery" on my web site to check this out:

Performance Oriented

Also, check your jetting to see if it is somewhere close to compatible to what I show is good for your engine. Be aware that idle jet sizes and mains also probably need to be up-sized for today's fuels. Look for "Happy Jetting" chart on this web page:

http://www.performanceoriented.com/performance-tuning-part-2/

[Trackrash]

Have you looked at the plugs? I have a similar problem. I believe it is oil fouling of my plugs. Have your rings seated?

Also what plugs are you running?

And you didn't say if the motor is completely stock and what carbs you are running.

[Laneco]

Grab a timing light and set the timing in the ballpark - I assume this has points and if so, I generally set the exact timing with a dwell tach. If this is converted to pertronix or other, then set the timing per specs. Then use the timing light on each plug wire (one at a time). You aren't looking for timing at this point, you are looking to see if each is firing consistently. This is the easiest, fastest, safest way to check for spark on each plug. If all 6 are hitting, and you have 6 plugs that are not oil fouled, your most likely culprit is a plugged fuel circuit(s) in the carburetors - se 1QuickS's post.

I assume you are running Zeniths - they are great little street carbs but the tiny passages definitely get mudded up with fuel.

angela