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  1. #1
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    Default Spark plug question - 304 black motor.

    Hey guys,

    recently got a Torana with a 304 in it out of a VL and its a standard HEI ignition system, early heads, Holley 650DP and TP dual plane manifold.

    I changed the plugs recently and noticed that 4 were burning very lean and the other 4 were very rich black and and sooty but not wet.

    Timing is set at 12 degrees, compression is around 150psi on all cylinders and its not missing at idle and starts fine so dont think dizzy is 180.

    have changed the jet sizes multible times both bigger and smaller and it only seems to make a difference to to the plugs running lean (other 4 a rich regardless of the jets)

    This happened after driving for approx 5km maximum...

    Any ideas on what would cause half to burn rich and half to burn lean?

  2. #2
    Part of the furniture BasicQ's Avatar
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    What # cylinders are lean and what # cylinders are rich?


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  3. #3
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    2 = Lean (white) 1 = Rich ( very Sooty)
    4 = Rich (sooty) 3 = Lean (white)
    6 = Rich (sooty) 5 = Lean (but ok)
    8 = Rich (sooty) 7 = Lean (but ok)

    Fouls up very soon after changing the plugs.... When I say sooty they are completely black and covered in carbon but they are not wet.

    Any advice would be appreciated.

  4. #4
    Part of the furniture BasicQ's Avatar
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    Quote Originally Posted by winx355 View Post
    2 = Lean (white) 1 = Rich ( very Sooty)
    4 = Rich (sooty) 3 = Lean (white)
    6 = Rich (sooty) 5 = Lean (but ok)
    8 = Rich (sooty) 7 = Lean (but ok)

    Fouls up very soon after changing the plugs.... When I say sooty they are completely black and covered in carbon but they are not wet.

    Any advice would be appreciated.
    Hmm.
    If #7 and #8 were the other way around there is the layout of the two planes of a dual plane manifold.

    Still could be manifold related.

    More on the carb?

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  5. #5
    Do you ever leave? EH179's Avatar
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    Could be many things here, including manifold distribution, leaking carb, weak spark and timing.

    Is the carb in good condition? Leaking power valve.
    Are the leads good?
    Plugs fitted correctly?

    My pet hate... not enough initial timing (12) for any performance 308, i like em around 18-24 deg initial or locked out.

  6. #6
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    All good points EH179 and BasicQ and thanks so much for taking the time to respond with some great advice.

    Regarding manifold distribution, it does have a 1.5 inch ported spacer fitted to a Torque Power dual plain manifold so maybe an overkill for a stock 308 but a lot of people do fit these without issue. Just put a vacuum gauge on it and running around 18 so plenty of manifold vacuum... it did rise from 15 to 18 after tweaking the idle screws which all improvements coming from winding them in (more lean mixture) but the driver side rear idle screw didn't seem to make a significant difference like the other 3 screws.

    2) Carb is basically brand new so shouldn't have any issues with leaking power valve but if that was the case wouldn't all the plugs be running rich?

    3) Have ordered a new set of leads to see if it makes any difference and worse case it will rule this out as a possibility. The coil lead did seem to have an average connection and wasn't a snug fit on the terminal. The lead also doesn't match the others so this could be producing an average spark under load. (Hopefully this could be the culprit)

    4) There was a shitty wiring job that I just found with a single wire going from the + on coil to the dizzy being spliced and shared with another wire that runs to the firewall (presuming that goes to the ignition). Have fixed that and now running completely separate to the coil terminal just to eliminate that as a potential issue. (Hopefully this could be the culprit)

    5) Plugs are new and definitely fitted correctly!

    6) Timing is running at 12 degrees but will try and crank it up to 14 and see if there is any difference (wouldn't this effect the condition of all plugs)?

    Any other suggestions or feedback absolutely appreciated.

  7. #7
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    Weak spark or bad leads could do it but they generally appear as an electrical miss usually starting in the upper revs. I got a sparky mate to check leads once and we found a dud with too much resistance, but there was a miss. Assume your HEI is the big cap? if so check the terminals on the inside. I have 2 and the original has alum terminals and they are pretty corroded where the rotor jumps the spark. The replacement has chunky brass and is much better.

  8. #8
    Part of the furniture BasicQ's Avatar
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    As already mentioned cover all bases with ignition first. Plug vac advance into direct manifold source if you don't already and see what that does. When all ignition is up to scratch and the problem persist try without the spacer under the carb. If you can, see what the engine vacuum is doing at different road speeds.

    So this is a close to stock 308 build with the Torque Power manifold?

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    Hi BasicQ,

    will try the vac advance direct to manifold as its currently connected to the carb port at the base which i expect is ported vacuum. Will also hook up the vacuum gauge and take it for a spin to see what happens (what should I be looking for as I am presuming it will drop as soon as I accelerate?).

    Yep pretty much stock 308 from an internals perspective with a dual plain TP manifold.

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    The T/P manifold is pretty much overkill for a stock 308. They rate them to 383ci. A stock manifold or performer would suit it better. Not saying that's the problem but it is a mis match. Also from memory some? stock VL heads were rather smog compliant?
    Last edited by RedTaxi; 04-11-2021 at 12:01 PM.

  11. #11
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    Quote Originally Posted by RedTaxi View Post
    ............ Also from memory some? stock VL heads were rather smog compliant?
    As sometimes happens at the end of production of something, stock VL heads are the best early head you can get, stock they are the large valve variety
    with hardened seats for ULP (yeah smog heads) and port paths are marginally better flowing than the supposed 'real good' B Cast heads. They also not
    prone to the cracking and the smog exhaust gas crossover is slightly smaller than any other early (less heat transfer from the exhaust)

    I run a set on the engine in the race car plus have a spare machined/ported flowed but unassembled set as well...
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  12. #12
    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by RedTaxi View Post
    The T/P manifold is pretty much overkill for a stock 308. They rate them to 383ci. A stock manifold or performer would suit it better. Not saying that's the problem but it is a mis match. Also from memory some? stock VL heads were rather smog compliant?
    As is the 650dp carb on a stock engine. Will take some patience to get that induction setup running sweet.

  13. #13
    Do you ever leave? EH179's Avatar
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    Quote Originally Posted by winx355 View Post
    Hi BasicQ,

    will try the vac advance direct to manifold as its currently connected to the carb port at the base which i expect is ported vacuum. Will also hook up the vacuum gauge and take it for a spin to see what happens (what should I be looking for as I am presuming it will drop as soon as I accelerate?).

    Yep pretty much stock 308 from an internals perspective with a dual plain TP manifold.
    Carb port at the base is manifold vacuum, not ported.

  14. #14
    Part of the furniture BasicQ's Avatar
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    Quote Originally Posted by EH179 View Post
    As is the 650dp carb on a stock engine. Will take some patience to get that induction setup running sweet.
    Yep, it’s the kind of setup that has people rushing out to fit Holley Sniper kits these days.


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    Quote Originally Posted by winx355 View Post
    Hi BasicQ,

    will try the vac advance direct to manifold as its currently connected to the carb port at the base which i expect is ported vacuum. Will also hook up the vacuum gauge and take it for a spin to see what happens (what should I be looking for as I am presuming it will drop as soon as I accelerate?).

    Yep pretty much stock 308 from an internals perspective with a dual plain TP manifold.
    I am assuming vac will drop. If it does and you have manifold vacuum from the base of the carby to the advance canister then you lose timing. If you have 12* now with manifold vacuum advance and when driving it drops somewhat then timing becomes less than you think you have. Check the timing with vac advance disconnected and port on carby plugged.


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