I have a very strange problem with a '78 351M motor with a 2 barrel carb.
The motor itself is sound and very good as far as I can tell. But here is
the problem. I can start the motor and get the motor up to normal running
temp. shut it off and restart with no trouble. But if the motor sits idle
for more than 1/2 hour it will not start again for 5 hours (or until cold).
It is as if the motor floods itself while sitting for this period of time.
I have tried a new carb on the motor, but still the same problem exists.
I am totally baffeled as to what the problem is. Can anybody shed some
light unto this for me? I would like to keep this motor as it is in great
shape for a '78 block
As you don,t have anything to test with the spark should be blue in color not
yellow or orange.But your coil shouldn't sound as if it has water go to the
auto parts and shake one of there coils:) If it sounds dry inside buy it.
It should be an oil-filled coil. If it has leaked, it may
not be able to stay cool enough. A coil for that is fairly
cheap and, coils frequently fail when hot. The coil should
have a nice blue spark capable of jumping at least a 1/4"
gap in open atmosphere.
I vote for the ignition module also, the next time it won't start, pour a
pitcher of ice water on the module and/or beat it with a ball peen hammer.
If it starts then, replace it. If it won't, replace it anyway and see if
that cures the problem. Mine had a habit of just dying on the highway.
Then you put it in neutral, turn the key and it would start right back up.
('76 460 same module)
I have a 400 in my '79 F-250 with a 600 holley double pumper and a Jacobs
omni pak aftermarket ignition unit. The same motor with stock ignition and
carb could be flooded and not start. With the above modification (Bosch
platinum spark plugs also) I cannot flood this thing. It always starts even
with several pumps on the pedal. The carb is tuned well so it starts
immediately with out the extra gas, but I tried one day to see what it would
do - even with the extra gas it started up just fine (with a healthy belch
of dark exhaust). I don't know if Jacobs Electronics still makes a product
like the OmniPak, but it's pretty slick since it bypasses the stock ignition
but leaves it in place. If the Jacobs ignition bites the dust then you can
bring the original ignition back online in less than a minute. Mine has
been trouble free for about 7 years or so. The hotter spark also improves
the engine's pickup - I can dump the holley with no bog, although that's
partially due to the carb setup.
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