Helping son with his 1986 IROC. Car has LG4 with T-5 Stick. All stock. Car has the original E4ME Rochester and HEI Distributor.

I have done a complete tune-up and rebuilt the carburetor. Getting ready to mount the carburetor and do final tuning. Want to check timing as well..

Need following info. I have the Chevrolet FSM for car.

1. Timing Pointer is rusted. The timing pointer on the timing cover is rusted and I cannot read where the zero mark is. The Hood sticker tells me to set timing at 0 deg BTC at 700 RPM. The FSM does not provide an accurate picture of the timing mark. The pointer on the timing cover has four saw tooths and there is a wide VEE between the left side and second from left side (facing front of motor). Is the Zero mark one of the points or in the middle of the wide VEE?

Where is the zero mark?

2. Cannot find the wire that needs to be disconnected to disable the Electronic Spark Timing. FSM says it is tan wire with black tracer near the rear of the right valve cover that has to be disconnected before setting timing with a timing light. I was able to find it on my 1990 L98 TPI Vette, but cannot find it on this carbureted 1986 IROC. Is the FSM wrong and it does not exist on the carbureted engine? The picture in the FSM shows a TPI motor but the write-up on setting timing that I am reading is for the E4ME Carbureted LG4.

3. The MCS Solenoid DWELL test connector. In order to tune the carburetor, I need to measure the dwell on the MCS solenoid. The FSM says there is a dwell test port in the right corner near the blower motor. I have located a green plug in that location with nothing connected to it,. It is coming out of the wire harness that goes to the ECM. Can anyone confirm if this is the MCS solenoid dwell test port?

To measure the dwell, do I put my dwell meter to this port and ground and measure on the V6 setting?

Thanks in advance.


Green plug near blower - blower is currently removed to clean vents


Thanks in advance.

 

OK,

Watched a few YouTube Videos....

1. The bottom of the wide VEE is zero degree BTC

2. The electronic spark timing connect (tan with black tracer) is in the left corner under the fan relay/vacuum pressure switch. FSM had it totally wrong.

3. I suspect the green connector is the MCS Dwell port but would appreciate someone's verification.

Thanks again.

 

on the large cap HEI disable EST control by disconnecting the four pin connector to the rear of the dist body. your FSM may be referring to the EST connector for the later small cap dist.

that green connector is the dwell diagnostic lead you need

 

EFFFFF all that crap about "mark", "tab", "book", "rust", "light", "EST", and EVERY OTHER BIT of that.

Set it to where the motor runs the best. Best thing about that is, YOU get to decide what "best" is. Could be any imaginable combination of max power, best throttle response, best gas mileage, easy starting, freedom from pinging, low running temp at high speed over long stretches, lowest emissions, fuel grade tolerance, ... WHATEVER is important to YOU.

We call it "tuning". Obviously there's LOTS of more handles on "tuning", in a general way, than just twiddling the distributor underneath a stock tune (ECM program); but if that's the only **** you have available to twist, then twist it to your best advantage.

Never forget the simplest axiom of engine tuning. Since YOU aren't the ENGINE, and nobody else is either, give THE ENGINE what it wants. It will tell you in no uncertain terms what that is, per the list of important parameters mentioned above. THE ENGINE knows better than YOU (or anybody else) ever will, what "timing" setting it needs, to deliver YOUR "best" performance.

In the words of one of the GOATs in a totally unrelated field, but that I can paraphrase to apply to engine tuning:

"If it RUNS good, it IS good."

Too simple, too eeeeeezzzzy. Don't outsmart yourself.

If you're REALLY concerned about "mark" and all the rest of that useless monkey-spank and bishop-buffing, then AFTER you get it to run THE BEST IT POSSIBLY CAN according to YOUR ordered priorities, whup out "light" and look at "mark" and "tab" and write down what you see, so that if some arrogant self-important yutz ever changes it, you can out it back where it belongs. Assuming of course that "mark" doesn't move, which it almost always does. Butt at least that'll give you some reasonable starting point for UNDOING whatever "improvements" some "mechanic" made to it.