I want to give as much info as possible so please
bear with me..
My 351C has a mild rebuild, with a RV cam
.030 over.. stock 2v heads , 2bbl motorcraft
carb.. ( for now..)
I just installed a set of dynomax headers
and 2.5 inch pipes, along with cats and
mufflers...
started the engine and she fired as always
so I let her warm up for awhile.. then shut herr
down and retighten all the header and exhaust
bolts..
restarted the engine and let it idle for a
bit, then started to bring up the rpm,, when it
reached around 1700 rpm she wanted to
just die....
I did not touch anything on the motoor d
during the header install... I rechecked everything
the I reset the time to 6 deg BTC..
After starting the engine again and loolking
at the timing marks, the engine is edleing at
about 20 deg btc.... so I backed off the
idel screw almost down to nothing.. still
show at about 20 btc... I did set the t timing
agian with the vacuum line off the dist.. at 6 deg,
but when hooked up to vacuum the timing is
back to around 20 btc... and no vacuum
at the carb ....
the dist is a ford duraspak, from the original
351m ...
any ideas...
by the way I did get the rpm up to around 2100
today...
but engine is running very rough..
Thanks
Best

ps.. the carb has F57 jets....

 

Are you sure it is Carb vacuum, not manifold vacuum?

You said it is a 351C and it has Cats? What year and model is it?

 

Hi Dan...
the Ranchero is a 77, the cleveland
is out of a 1970... you had me thinking for
a minute, but then I realized that I do
have break pedal, which is off the intake
manifold... but I will double check that this
morning...
Would not think that cats would effect
the vacuum of the engine....
I was talking to a guy who use to build
engines at Carrol Shelby's in Carson Cal
and did not think that should have an y
effect, but who knows, I have not done this
stuff in a long, long time...
thanks
Dave.
ps: but why is the advace so far ahead
at idle..... Damn, Damn, Damn.....
it seems easier to work on someone
elses cars then my own....

 

Leave the vacuum hose off the distributor, plug the hose with a screw or small bolt. Run the motor, see how it runs. Then remove the plug from the vacuum hose and check for vacuum. If there is vacuum from the hose at idle, then it is manifold vacuum not carb vacuum.

 

20 degrees at idle isnt too bad (including vacuum advance). Is it automatic? You might have pulled or burned off the vacuum hose to the modulator.

 

this morning I reset the timing at
6 deg BTDC. then hooked a vacuum gage
to the vacuum port for the dist... No vacuum.
Then I hooked the gage up to the intake
and it shows a steady 15 " vacuum at
around 600-650 rpm.. but the
harmonic show about 25-30 deg advace..
this is way to much... could it be that the
cetrifugal springs on the dist might have broken\come off thus advancing to fast?
I just can not explain how I can go from
6 deg to nearly 30 with such a small
rpm increase..
But then why is there no vacuum at the
carb port??..
I did not find any vacuum leaks ....
Best
Dave

 

There will not be any vacuum at the carb port at idle. The carb vacuum only come in when the throttle starts to open. The manifold has vacuum at idle and steady 15" isn't too bad. Put your vacuum gauge on the vacuum line at the dist.

Is it carb vacuum (0), or manifold vacuum (15").

 

Hi Danlee
well I'm pulling my hair out, this is
not very good....
I've reset the timing about 5 times
now and still can not get the car to idle
correctly or get past 1700rpm, once I
got up to 2100...
I may have left a point out.. I am
running a duraspark Dist.. (cir: 1977)
in fact the other night I rebuilt it.. so I
no its good, and the gear drive was in very
good condition.
I am leaning more to the Mallory
Hy-fire VIA... it seems to be the only
logical point for this to be happening....
Even thought maybe a rev limiter was
coming on, but this model does not have
a rev limiter.... but I think it would be one
reason why the harmonic balancer timing
show 30 deg advance when the car is at
about 600 rpm... ...
hate to go out and spend any money on
a new ignition box, when I don't know what the
problem is..
Do you have any idea on how I could
by pass the malory and just run a stock
type ignition circuit??? its been so long.
and of course I have disconnected all the
old dura spark wiring...
Best
Dave

 

I don't know what I did this morning, but
the cleveland pulled to 3500rpm .
I again reset the timing , ito factory 6 deg
BTDC, then got it ideling.. at around
600rpm... then I advaced the dist a little
untill she smoothed out..
At idel she seems a lttle rough, and loping
but I'll work on that... these are the same
steps I have done for the last week,
Anyway, Thanks to all for your help..
Best
Dave
PS: I hope this works out.. have not
driven it yet.