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Discussion Starter · #1 ·
1975 351W w/50k or so miles on it. just fininshed swapping it into an 80 F150 - replacing the 300ci straight 6.

351 is stock and tolerances are within specs.
2bbl card and pointed distributor to keep it simple.

under power the thing runs very strong.
has a bit of a rough idle - about 700-800rpm
puttin down the road with light throttle she runs rough - almost a jerky feeling...

tested for vacumn leaks (several times) using carb cleaner - didn't find any. new plugs, wires, cap, points and rotor and coil....

i *KNOW* there's a simple resolution and these symptoms point to an easily resolved "tweak".......
just can't quite pull it out of my cobwebbed memory...
your feedback is much appreciated.....
 

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Did you use dielectric grease on the plug boots? Sometimes they'll back out of the cap if you don't burp them. Make sure that they are all fully seated.

And regarding vacuum leaks... Courtesy of TheOldWizard... Don't forget to remind folks to check the PCV valve, hose and grommet !
 

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Did you make sure the mechanical advance AND the vaccum advance were BOTH operating correctly/moving freely?
 

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i have been reading alot about plugs on here that some motors only like motorcraft plugs. Second, i would try a fuel filter, the one at the carb, older truck may have sent some crud up there but not enough to interfere at higher speeds of third fix it "like they do in mother russia"(Armageddon) beat it with a big hammer till it works
 

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Discussion Starter · #6 ·
what i've done so far.....

Thx all for the input ..... so far.....
-- dielectric grease / spark plug boots. never used the grease. all plug wires are well seated..

- pvc valve - just sitting there on the valve cover - not connected to anything yet. Only power brake booster & vacumn advance are used in this installation. - also installed a new EGR valve.

-- distributor - is new - not remanufactured. pulled it/spun it & validated mechanical advance functions. sucked on the vacumn port to validate that advance works too...

-- aluminum carb spacer plate - not on this engine. carb with a couple gaskets sits right on the manifold. new gaskets, new bolts

-- motorcraft plugs - always use'em in FOMOCO products, Champion in Mopars, DELCO in GM and only NGK in my japanese vehicles.... just what i've found - over the last 30 years - works best

-- fuel filter - removed "stock" filter at the carb and drilled it so it's straight-thru. installed in-line clear plastic filter so i can see the fuel flow and any crud from the tank. no issues there...

anyway -- the struggle continues.......


here's one more item that caused me a lot of headaches....
adjusting the valves on this engine......
There's a special "trick" for the 351Windsor engine -- can't use the normal pre-load rules...if you do (spin pushrod, tighten until no movement then another half turn) rocker arm nuts loosen in about 25 miles and the valves don't open ...... anyone have a clue??? took me 6 weeks of deep digging to find the resolution...
 

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Are you running manifold vacuum or ported vacuum to the distributor.it makes a difference.
 

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351

here's one more item that caused me a lot of headaches....
adjusting the valves on this engine......
There's a special "trick" for the 351Windsor engine -- can't use the normal pre-load rules...if you do (spin pushrod, tighten until no movement then another half turn) rocker arm nuts loosen in about 25 miles and the valves don't open ...... anyone have a clue??? took me 6 weeks of deep digging to find the resolution...
I normaly do it with engine running, adjust each rocker till the lifter quits chattering, then three quarters more, one quarter at a time. but i thought the 75 motors used positive stop rockers. just torque to specs.
hope this helps
 

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I have a 1994 4.0 Ranger and every now and then it will pop off the right rear plug wire and start skipping. Even a computer could not find it. So, check it in the dark and you can see it sparking at the block area. :)-O)
 
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