Col Wickham

My 1972 455 is pinging under power and running on when turned off. Classic advanced timing / low octane issues.
It has a Delco Remy HEI distributor and is running AC Delco R46SZ plugs set at .080. Sounds wide but I've seen in other threads where this is the norm for these plugs. The car has a fairly lumpy cam.
I'm running high octane fuel with a little octane booster in it. I've backed the timing from 8 deg to 5 deg and I'm still getting pinging and pre-ignition. If I go lower you can hear the engine doesn't like it.
One thing I don't understand is why the No1 lead is running from where the No4 lead runs from in a standard distributor according to the Service Manual. Firing order is correct from there, but why would this be the case? If you check section 6c-7 in the 72 service manual my leads are 2 spaces ccw of where they should be.
Does this matter?
The other thing that's bugging me is the fast idle screw doesn't seem to do anything no matter which way I turn it.
Ideas?

panos

What are the motor specs?comp,cam,etc? im not familiar with those plugs but it sounds quite big for a gap? sure someone will chime in on that.About your idle screw,did you check for vacuum leaks?
good luck with that.



Panos

joe_padavano

0.060-.0.080 is typical for plug gaps on HEI systems, but keep in mind that the whole reason for the switch to HEI was to satisfy the EPA requirements that cars be able to meet emissions requirements after 50,000 miles (and later, 100,000 miles) without a tuneup. The larger gap, in conjunction with the higher voltage coil, was intended to reduce the possibility of misfire with the leaner mixtures common in these early emissions-compliant cars of the 1970s. If your carb is stock and you regularly tune the car up, you can probably back down on the plug gap.

The only thing that matters is that the rotor is pointing to the plug wire for the cylinder that is on the compression stroke. The fact that no. 1 is clocked differently from stock just means that the distributor was installed at a different position from stock. That's really not important so long as the plug wires reach the appropriate cylinders.

Keep in mind that the fast idle screw is only functional when the choke is closed and the fast idle cam is rotated into position. Once the choke opens, the cam is rotated clear and the fast idle screw does nothing. To set the fast idle to spec, you need to manually rotate the cam back into position so that the screw sits on the appropriate step on the cam. The CSM will tell you which step to sit the screw on for the adjustment.

dc2x4drvr

I would start by verifying that the outer ring on your balancer hasn't slipped, do you have access to a dial back timing light? That would allow you to check timing at say 3000 rpm. Any idea how much compression you have?

Col Wickham

I only have a standard timing light. I don't have a compression guage either. It's supposedly 10.5 :1
I'll head back up the shed with the CSM today and tinker some more. Think I'll be handing it over to someone who knows what they're doing. I've knocked it back to 4deg last night so I'll take it out and see what difference that made.

Joe: Thanks for your clarification on those issues mate. The choke was open while I was twiddling with the fast idle so I'll play with it again with it closed and the cam follower set properly. I was trying to get it idling at 1100 like the good book says before timing it but it idles at around 850-900 when hot in park.

joe_padavano

Be aware that you want the choke open when setting the fast idle to spec. What you have to do is hold the throttle lever slightly open with one hand, move the fast idle cam into the right position with the other hand, then release the throttle lever so the fast idle screw holds the cam in position. The specs are written assuming this configuration with the engine fully warmed up and the choke open and allow for the fact that the speed will actually be different with the engine cold and the choke closed. Also note that different years may have the screw in different positions of the fast idle cam. If you look at the cam, you'll notice that it has several steps to knock the idle speed down as the choke opens. Usually the CSM directs you to set the fast idle screw on the second highest step, with the screw up against the step to the highest speed.

Col Wickham

Hey hey thanks Joe. I'm learning about these carbs and I did try setting the fast idle then the timing with the cam on the first step and choke closed. Was fine until the car warmed up & the automatic choke cut out. Timing went to somewhere around 3deg after tdc...not good. You explain it a lot clearer than the CSM so thanks again.