Dave: A few things come to mind here. I'm not sure why the timing
variation in itself would cause a "misfire" if the cylinders are all
still seeing spark within 4 or 5 deg. Still, if you have tried different
distributors, let's assume that the problem is before the distributor
drive. A sloppy and/or worn out timing chain can give the distributor
imprecise rotor position, so here's a way to check this:
a) Remove the distributor cap
b)Take out the spark plugs and move the engine forward by hand to where
the cover pointer is right on one of the timing numbers.
c) Note the exact location of the rotor.
d) Move the engine backwards, and see how many degrees it takes on the
pulley before the rotor starts to also move backwards. (It should follow
within two deg.)
If it's much more than this, there is lost motion between the cam's gear
and the distributor drive gear.
The Pertronix claim to nullify distributor shaft wobble (Point/timing
variation) should exclude your timing variation.
Other tidbits....If your timing is set to fire at, say, 12 deg. BTDC at
idle, your rotor should be nearly centered under the cap terminal. If
the rotor is obviously between cap terminals, the spark then has a
choice of where to send a spark. Not good. You can also check this when
doing d) above.
Let us know when you get this sorted out!
Dick
From:
murr32@shaw.ca(Dave Murray)
I have a timing stability issue at high RPM. The timing varies by 4 - 5
degrees at engine speeds greater than 3000 rpm. I have tried 2 different
distributors, 2 different drive gears, points, a Petronix, and a Crane
XR700 ignition module. This high speed misfire/timing problem is the
only thing keeping me off the road, any suggestions?
Dave
|