Hi. I have an IROC '86 with a modified (heads, manifold, exhaust) LG4 (305 cui, computer controlled carburetor) that seems to need timing.

The book says that I should check a label in the engine compartment for the correct advance, but there is no such label there. And I see people on the net claiming it should be everything from 0° to 15° advance.

So what is correct? And how do I measure it?

I should yank the connector with the orange cable that reside close to the window washer fluid cistern, right? It disconnects the computer?

With the strobe lamp dialed to zero and the car idling below 1000 rpm the advance should be ??? degrees?

Then people speak of raising the rpms to 3000 or so, and adjusting the strobe lamp to say 30° and then the marker on the harmonic balancer should read 0° or something with a distributor vaccum hose disconnected? I get lost here.

My guess is this applies only to non-CC cars, right? So I only need to set the base advance on my car?

Grateful for any help.

 

If it's been modified, then the original factory timing spec won't be "right" for the motor.

But if you're one of THOSE that's just gotta see a number lit up by a blinking light, then this is how to do it.

Shut the motor off. Disconnect the large Weatherpak connector that hangs out of the base of the carb; has 4 wires in it. (Not the harness with 3 wires that goes to the cap, but the other one). Crank the car up. It will run like hammered dog plop. Set the timing to whatever number peels your banana. I'd suggest 6° BTDC as a starting point. Shut the motor back off, hook the 4-wire Weatherpak back up.

Then adjust the timing properly for WHAT YOU'VE REALLY GOT. Give the engine what it wants. It'll probably want to be advanced somewhat more than the factory "spec". Just as a clue, advance it until it starts to ping, then back it off until it quits. That's probably going to be too much; but it'll give you an idea of what range you have to work with.

 

I appreciate your advice, but the "twist the dist by ear" method is what left me with a snarling and coughing sick engine.

When it sounds good at idle it starts to stutter at load. When I make it run clean at load the idle is crap.

Putting a new dist cap and rotor improved things, but it is still no good and I want to blueprint the settings before I proceed to troubleshoot other components, like my carb which I suspect is faulty.

When I pull the computer cable (?) I mentioned and set the timing to 6° or so, it still advances when I push the throttle and rev a little, albeit only a few degrees.

When I put back the computer cable the advance jumps to like 12-15°. Ain't that a bit much for idle? And what does it ought to be when I rev it at 3000 or so?

 

When you unplug the CORRECT connector and set it to 6°, and then plug the connector back in, it should go to more like 20° at idle.

The connector you're talking about isn't the right one.

Sounds to me like whatever is wrong with your car is not a function of ignition timing. Put it where it belongs, or some reasonable approximation, and leave it alone; and troubleshoot the car.

People ascribe WAY too much significance to the "number" that their timing light says. The engine will run perfectly fine over quite a broad rangewhen all is working right. If it doesn't, then there's something else wrong; and dinking with the ignition timing won't fix it.

At 3000 RPM it should be at around 36° with the correct timing setting plug connected but the vacuum line to the MAP disconnected; and around 46-50° with no load on the engine, and everything connected and working normally.

 

I much appreciate your advice in general and some numbers to go after in particular!

I do suspect that my carburetor is out of whack, it will be the next thing I will address after changing the ignition coil and module now.

Thanks!

 

Strange thing:

When I start the engine it runs okay for a while, but after 10-15 minutes of driving it starts to cough, stutter, make exhaust explosions and behave VERY badly.

When I unplug the orange cable (now verified to be the ECM power) the car runs great, albeit a tad tired in the upper rpms and the occasional irritated weak cough in the lower with lot of throttle.

When I measure the advance with the ECM unplugged, it's 6-8° and increase to some 20+ when I rev it. This makes me confused, I would think it should not move at all with a CC distributor?

Something is messing with my ignition advance, and I don't know where to start looking. =( Help?

The distributor coil, cap and rotor is new, the carburetor is old, the EGR is replaced with a block-off plate.