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My motor pings, without getting on it too much. I have a small block chevy - thumper cam, aluminum heads, edelbrock carb and manifold. How do you set the timing correctly? I run 91 octane gas, but when I begin accelerating, the motor pings. Should I just keep moving it back, until it doesn't ping?
What type of ignition/distributor are you running?Quote:
Originally Posted by Simi Mike
first thing to do is to check the timing and see where it advances to total at 3-4000 rpm(what ever rpm it stops advancing at)
It should be less than 40 and probably you will have to back it down to 35-36 before you get rid of the ping--when you get it backed down enough that the ping is gone, check it to see where it is at at the higher rpm and also at idle rpm--you may have to recurve the advance in the distributor so it won't be lazy off the bottom rpm
Hey Jerry,Quote:
Originally Posted by jerry clayton
I know the old springs & weights method, and I know the spark map method of the ECM control method, but how do you accomoplish re-curving with an electronic distributor that's not computer controlled. I missed that piece in my ignition education.
Roger--the non computer electronic dist use the springs & weights--in fact, all the MSD dist use copy of the GM weights and springs just under the rotor!!! The Msd and similar boxes do allow/have the ability to retard the spark from the mechanical triggered number--like for starting, or boost related, NOS, etc
I have the timing running about 36 degrees, and it still pings. As far as my
distributor - I'm running a Mallory HEI Dist with a cross fire Dist cap. How would
I know, if I have it set too far back. The way it cranks over? Kinda slow?
You'll need either a timing light that you can dial in the advance on the light itself, or a degreed dampner that you can read the degrees on with a conventional light to see at what rpm the advance starts coming in, and at what rpm it is fully in to know what the advance mechanism in the distributor is actually doing. You also need to know what your initial timing (degrees advance at idle speed) is....
I would looking for total of 32 degrees or not much more than 34.
how old is the fuel in the gass tank? was TDC checked dammper to timming tab when engine was built . look at reworking the curve if msd there is springs and limit bushing you can re work it and are you using a vacuum AdV on the dist ,check vacuum running down the road
Hummm.Maybe check to see if it is one tooth off.......
Mike,
Pat asked about the gas. Is your 91 octane fuel an ethanol blend or straight gasoline? An ethanol blend will start phase seperation within two weeks of storage, and as it seperates you will lose 5 to 6 points (or more) on octane rating - your 91 will actually be 85 or 86. Are you using a good dial back digital timing light, where you can set your rpm at say 3500, and dial it back until your timing mark zero's out on the dampner to pointer? If so you should be saying, "It's running 36 degrees total timing", not "...timings running about 36 and it's still pining." If you have a good dial back light, run your rpm's up until the timing stops advancing, and dial it back to see what the actual value is for your engine. Rotor position (which tooth you hit on the cam) is only important if the adjustment of the distributor base is restricted in some way, or if your plug wires are too short to allow the base to be adjusted to compensate for the rotor/cam position. You can be 180 degrees out, and as long as you can spin the distributor base 180 degrees you can set your timing accurately. It may look goofy, but it does not really matter in the way it functions.
If you have good gas and know that the timing pointer & TDC mark were properly aligned during the build then I would start backing off the total timing a degree at a time until it quits detonating. Once there, check the timing at idle & no vaccum advance to see where you are. Depending on what you find you may need to re-work the timing curve with springs & stops like Pat & Jerry mentioned. If you don't have a good, digital dial back timing light then you need to either buy one, or find a friend who has one and knows how to use it. To me 36 degrees total timing is not a high number for the engine you describe. Old, phase seperating ethanol blend gas that's been in your tank for weeks/months is a really good possibility here, IMO. Let us know what you find.
Well - I might know where I'm going wrong now. I am using Shell 91 octane
gas. It seems to run the best, but the method, I set the timing, - - probably
isn't the right way, as you explain above. I'll try running the rpm's up, and then
set it, and see what happens.
Mike,
You need to set your timing at about 1000rpm, no vacuum advance, no computer input at say 10degrees BTDC. Once set run it up to 3500 to 4000rpm using a good dial back and see what your total timing is with the current distributor setup. Just my $0.02.
Thanks Roger