Hi again fellas.

I been tinkering w/the carb and timing w/this 454 trying to get the smoothest idle possible.

GMPP recommends timing at 4* BTDC. Why is this so far off from the 16-20* that everybody here is running? I also noticed that the 502 is to be 8*.

One more question. What make for better idle: Lower initial timing/higer idle speed screw, or more initial/less idle speed screw?

Thanks

Vince, that 4 deg initial assumes you are using the GM HEI that they have calibrated for that motor. You should really time the motor for full advance (about 36 deg) and let the initial fall where it may. The way I have done it is to mark the balancer at 36 deg ( your balancer is marked I think). Disconect the vacuum advance and rev the motor until it reaches max timing (36 deg mark reads at TDC on the timing tab). Adjust as necessary.

Vince,

Hi Vince,

If you don't mind, I would like to just add a few mis items onto what is stated above.
As I understand it, using the full 36 degrees, is for max performance. This is normally done when you have changed from the stock cam, etc.
If the engine is stock, keep it right where GM recommends. That will most likely give you the best idle. If it's not stock, then you may have to play with the setting. The last 383 that I built, didn't like a total of 36, but ran much better at 33 total. My 396 runs great at 36 total, but it clearly hurt the idle a bit. I also have a bit of a surge now and then at 36.

If the idle speed screws have already been set, I would leave them just where they are. After you get the timing set, set you idle to an RPM you like and you should be good to go.

Fred.
SS 396 Blue Chevelle

timing can be set at idle by ear basically its not the most correct way but can be done turn distributar slowly when idling listening for the highest idle you can acheive then back it off a hair lock it in and your ussualy good as fas as idle mixture screws go dont do them till timing is done then crank them in until it stumbles bad then back out a turn in a half... the correct way to do your timing is as stated above by someone else with engine at 2,800 to 3,000 rpm and vacume advance diconected try for 36 to 40 total if you are using a regular light with no advance dial on the back you will need timing tape so there are numbers from one to 360 all the way around your balancer can be had at any speed shop for around 5 to 8 dollars and just sticks right on rather easy and a good 5 dollar investment unless ya have the good light

I set my GMPP 454 at 14* BTDC. It falls at about 34 degrees total and runs great.