Ignition timing 401 1966GS

I recently purchased a 1966 GS. I have very little knowledge on the 401 nailhead engine. The car idles well and sounds good and drives at part throttle neighborhood speeds well. The problem is when I floor it from any speed it bogs and doesn't want to rev, starts to sputter and make sputtering noises. It does this out in park as well. I have visually verified the accelerator pump is squirting 2 streams. It smells rich at idle. I have compression tested cylinder 2 with a gauge that will not hold, from the seat I could see it reach more than 125psi less than 150psi. I believe my problem lies in the timing. I pulled the vacuum advance line while running at idle with no apparent change. I put a vacuum gauge on where I removed line from carb (ported) and got 5 inches vacuum that went up as I opened butterflies. I attempted to check with a standard timing light on cylinder 1 (pass side under ac pump) and cannot see the mark anywhere near the timing indicator. I verified correct plug wire and firing order for all cylinders. I found the timing mark with the light by laying down on the ground. It is at approximately the 7-8 o clock position indicating so much advance I can't believe it is running. Pulled all plugs R43S and the only one that was different was #4 very black, the rest tan to medium brown. I brought the tdc mark on the balancer to 0* and piston 1 appears to be at tdc when a straw is inserted into the plug hole. I pulled the distributor cap at this time and it appears that at tdc the rotor is halfway between cylinder 1 and 2. I think this confirms too much advance. I would be unable to rotate the distributor enough clockwise to correct this as the vacuum advance is nearly touching the firewall. How do I resolve this to get the timing corrected.

I will be ordering a new compression tester to check all cylinders.

 

i think if it was advanced it would be between cylinder 3 and 1. am thinking it' retarded.

 

Entirely possible your timing chain is stretched. My 66 401 had a very slack chain.

 

I have read 401 nailhead firing order is 12784563, is this corrected? If so with the rotor past 1 and half way to 2 at tdc on 1 is that advanced or retarded? I dislike ignition stuff as it confuses me.

 

Would a stretched chain cause advance or retard issues?

 

It would retard cam and ignition timing in relationship to piston position

 

Set your distributor cap off to the side, so you can see the rotor. Put a socket on the crank bolt. With a breaker bar on the socket rotate the engine until you see the rotor move stop and go the other way. If it moves immediately you should be good on the timing set. If the crank moves a bit before the rotor you have at least 1 issue.
Let us know

 

And be aware #1 cylinder is on the passenger side.

 

You would have to pull the distributor, turn the oil pump shaft back ccw with a screwdriver a few degrees, then reinstall the distributor. It may take a few attempts to get it all aligned properly.
It would be helpful if one of us could take a pic of our dist at tdc (any volunteers?). I'm rained out for the next two days....

If you are not getting a difference in advance with the vac line connected/disconnected, you may have a bad vac advance canister.
These are pretty much a requirement for testing. Harbor Freight has them too:

 

The harmonic balancer/damper is a two piece with rubber isolator, and old units can slip and that will move the timing mark.

You need to be 100% TDC on number 1 and verify the timing mark on the damper if on zero.

Make sure you move forward and back on the crank and note when the piston moves on both sides of the dwell so that you can "split" the difference and be in true TDC and see where the timing mark and zero on the tab are in relation to each other.

If it is within a couple of degrees, you should be OK. If it is way off, that indicates the damper ring may have spun, and you will need to deal with that.

Then you can start one checking for chain stretch by how much "slack" there is between moving the crank and when the rotor moves, same thing, back and forth to get the total.

 

Thanks for the replies. After work I am meeting another buick friend and will check out his 401. The points, condenser, cap and rotor appear to be new. I wonder if the shop that did the work removed the distributor and put it back in a different position. The car had sat for a long time and was towed to a shop to be looked over. They replaced fuel tank and rubber lines for sure, brakes, and a dew other things. I do not know this shop. I have heard of people pulling the distributor to spin the oil pump after long periods of sitting.

Josh

 

you said you removed the line from ported side and got 5 psi, you should have no vacuum on the ported side, if that is really so seems like your carb throttle blades are open to much from turning idle screw to far in because of a vacuum leak or retarded timing and you trying to compensate by turning the idle screw to far in. if you were getting vacuum to the vacuum advance and then pulled the vacuum line of with no change to the timing or your idle rpms does not go down then your advance is not working, check to see if your mechanical advance is even working. start by putting your hand or rag over the carb and if your idle speeds up you have a vacuum leak that will eliminate one thing anyways.

 

just read your post again you said your trying to turn dist clockwise that is retarding the timing, nail heads go counter clockwise to advance timing

 

There seems to be little to no slack in the chain. When I go back and forth a bit on the pulley the rotor seems to move at the same time. Waiting on compression tester to show up. Also waiting for a helper this weekend. I checked out a friends nailheads and the vacuum advance was in a much different position. I am leaning towards pulling the distributor and resetting according to the chassis manual.

 

Ok got a helper today and confirmed compression stroke cylinder 1 (pass side) by holding finger over plug hole while it was cranked, balancer mark coming around to tdc at the same time. Again appears to be little to no slack in chain as crank is moved back and forth to get to 0* on tab. Rotor double checked as past terminal for 1 and half way to 2. Got the chassis manual out and the pictures show rotor and vacuum advance in a much different position. Going to pull distributor and realign according to manual. I can only think that it was installed off by a tooth or more before I purchased the vehicle.

 

good luck, your not reading my posts #2 and #13 . 1 and half way to 2 means it's after top dead center ATC, retarded. after 3 and just before 1 is before top dead center BTDC that's where you should be plus your turning the dist clockwise and that is retarding it. if am wrong someone please correct me. either way good luck over and out.

 

You are correctthe rotor is past 1 when 1 is tsc. If the piston is at tdc and the rotor is long past the firing point for 1 wouldn't that mean that I fired long before tdc 1 making it advanced? If I try to turn the distributor counter clockwise to retard the timing it seems as if the cap would rotate towards terminal 2 and farther from 1. Please help me understand where I am making my mistake in logic, I only want to do this once and if I am wrong I want to understand how. I believe the engine rotates clockwise and the rotor does too.

 

I think I have cause confusion with my clock references. When I said 7 o clock that is where the balancer mark was when the timing light flashed. The rotor when cylinder 1 is at top dead center is between plug terminal 1 and 2 approximately 9 o clock if looking at the picture Larry posted. Rotating counter clockwise would then make #2 terminal get closer and farther from #1.

Or am I still confused?