Irv Korey wrote:
> > Thanks for all of the prompt replies to my firing order inquiry! The
> > saga continues: I suspect my timing marks are off as the car runs awful
> at
> > 4 degrees after TDC (doesn't run smooth without backfiring until the marks
> > say 6 degrees before TDC)... Measurements taken with vacuum advance hose
> > removed. I just came in to grab a coat hanger to try to verify my
> marks...
> > If the marks are right, what could I be doing wrong?
>
> Not much. US spec cars were timed for emission control, not to run well. The
> 4 degrees after timing spec is correct for my 74 but I haven't had it there
> for years, and the car passes emissions tests here. Go ahead and advance it
> some.
The 4 degrees ATDC timing was almost always (AFAIK, always) for cars
with vacuum retard units, and that was dynamic timing at idle, all
vacuum units in operation.
The timing only SOUNDS horrid until you remember that, at idle, the
vacuum retard unit is retarding timing by a great deal, and as soon
as you are off idle the retarding stops.
So essentially, with the vacuum retard unit fully retarding,
4 ATDC makes sense, as soon as you hit the throttle it goes into
a more sensible timing range.
All too many times cars are "desmogged" by some cowboy who
doesn't learn what everything does, and then surprise surprise,
it runs like hell, which they then blame on emissions junk.
Check the vacuum line, it's likely retard. If it isn't, something
has been changed.
If it's retard, leave it on, time at 4 ATDC, that should run
well. If you want to advance it a few degrees from there, the
usual disclaimers apply, some gains to be had, some losses, but
have fun with it. But start with what the factory intended.
Face it, who really knows more about these cars, the guys
who designed them EVEN THOUGH they had to deal with emissions
laws? Or the greasy monkey down the street who keeps telling
you he loves your car because he's always had a soft spot
for "these little Italian cars".
--
Trevor Boicey, P. Eng.
Ottawa, Canada, tboicey@brit.ca
ICQ #17432933 http://www.brit.ca/~tboicey/
"You can't crush cars with a university degree."
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