Mike,
The full advance was 54 degrees total.
Diagnosed as 16 base, 20 degrees mechanical, and 18 vacuum.
The shop said I had a "high speed timing miss-fire, probably too much
advance".
They suggested,
1. Retime to 10 degrees base,
2. Eliminate or restrict the vacuum advance
3. Clean the plugs
Per my previous post, I've tried 10 and went back to 16 advance.
I've eliminated the vacuum advance. That should get to 36 total.
Per shop, "The engine is too rich, 5.5% CO at high speed."
The carbureter was just rebuilt and may need to be rejetted. The shop wants
to rejet and check the power valve after the timing is fixed (done).
More details.
This is the Motorsport 5.0L GT-40 SVO, M6007-B50, with B303 cam.
The distributor is MSD 8352 with vacuum advance, no external boxes.
The motor has 500 miles on it.
When I pulled the plugs, they were all very sooty black but not fouled.
I have a bad surge at low speed in lower gears, which is why I wanted the
carbureter checked for rejetting or adjustment. That surge is there in
higher gears, just less noticeable.
MSD installation notes offer the following:
FACTOR ADVANCE TIMING RETARD TIMING
FOR FOR
Cylinder Pressure Low High
RPM Low High
Vacuum High Low
Energy of Ignition Low High
Fuel Octane High Low
Mixture (air/fuel) Rich Lean
Temperature Cool Hot
Combustion Chamber shape Open Compact
Spark Plug Location Offset Center
Combustion Tolerance Low High
Load Light Heavy
Since I have restricted the advance timing I will return to the shop for
rejetting and check the results. Any advices are always welcome. I will
post results as available.
Thanks,
Curtis
At 11:06 AM 8/5/01 -0700, Mike Sutter wrote:
>What is your full advance timing?
>
>What camshaft are you running?
>
>I had recently been experiencing a slight rise in operating temperature with
>my Motorsports crate. The first thing I checked was the timing, sure
enough it
>was off. Too much advance. The distributor was allowing the timing to advance
>to about 42 degrees total.
>
>Consulting with wiser members of the list, I have heard that 36 -38 degree
>BTDC is where a small block Ford wants to be at full advance.
>
>When I originally assembled my ignition system I went with a full mechanical
>(no vacuum) advance system. The distributor was curved to 1 degree at 1000
>RPM, 16 degrees at 2000 RPM and 26 degrees at 3000 RPM. With this set up, all
>advance was in by 3000 RPM. I static timed it at 10 degrees for a full
advance
>of 36, all in by 3 grand.
>
>I have heard of guys running as high as 50 degrees full advance and they
claim
>"that's where it runs the best". I assume that the further you advance a
spark
>in the cylinder the more you are prone to ping or prematurely ignite the air
>fuel mixture. This causes the engine to run hotter.
>
>I would also like to hear other opinions on this subject.
>
>Mike Sutter
>'66 Tiger
>
>
>Curtis Fisher Wrote:
>
>"I was having carbureter work done and they said the base timing was too
>high, 16 degrees. I know the Motorsport sticker said 10 degrees BTDC and I
had
>tried that but it ran much better at 14-16 advance, where I left it.
>On advice of the carbureter shop I reset it to 10 degrees advance. Not only
>does it run worse, it runs hotter, in the 195-200 range. I called Motorsport
>and the tech suggested 16 was where he always sets his. Back to 16, no
>problems, better cooling, better running."
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