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cam timing

Discussion in 'The Garage' started by BIGBIRD, Apr 18, 2002.

  1. BIGBIRD

    BIGBIRD Registered Member

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    Can't get my 350 to run clean. After going through the carb and ignition decided to call the guy that put the motor together (couple of previous owners). He said it was set up like a race motor. When I asked him why the motor wouldn't run anywhere near correct timing he said the cam was degreed and that you could no longer set the timing by stock marks. I thought maybe the balancer had slipped.. To me that means the cam is dead nuts on but that the motor should still run per spec. I was shooting for 12 BTDC @ 900. Timing marks now show up on the opposite side of the motor with the timing light on them. I would say that its advanced about 40 - 50 degrees BTDC at idle. Motor has a stage 2 cam with 1.6:1 rockers, stock HEI with curve kit.

    Am I missing something ? Do they screw with valve timing that much ? Motor runs good but is always rich.
    Anyone have any suggestions?
     
  2. Twiz

    Twiz 1/2 ton status

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    <blockquote><font class="small">In reply to:</font><hr>

    Motor runs good but is always rich

    <hr></blockquote>
    Care to elaborate?

    Does it ping or miss? Hard to crank? Back-fireing? (might indicate possibe ignition problems)

    If he degreed the, it means he advanced (or retarted) the cam in relation to the crank, the timeing marks should still line up, TDC is still TDC.
    If the dis was off a tooth, you might not be able to line up the marks. -maybe-
    Was the vacume advance removed before setting the timeing?
    Is the vacume advance hose pluged into the carb in the correct location?
     
  3. Thunder

    Thunder 3/4 ton status

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    If the cam timing has been modified the best way i know of to adjust the timing is with a vacume guage.
    Hook up the guage to a port that gets get full manifold vavume.
    Disconect and plug vacume advance.
    Adjust timing to get the highest reading on the vacume guage at idle. That will get your timing very close to right on.
    Your timing marks may be off because who ever built the engine may have used a harmonic balancer whos timing marks did not match the timing indacator on the timing chain cover.
    Changing the cam timing will not change TDC.
    If the motor was built as a race engine it may have larger jets in the carb than it needs. mabt that is why it is running rich.
    What kind of a carb are you running?
    If you have a holley you may have a bad or the wrong power valve.
     
  4. BIGBIRD

    BIGBIRD Registered Member

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    Thanks for the replies. It's really weird, the motor runs too good to run bad if you know what I mean. Smooth, no pings or misses. There is sometimes a slight skip that I don't think most people would ever detect. The distributor advances correctly, replaced the pick up due to skip, had no effect. Right now I advance the timing until motor gets real crisp and won't take a load well, never really detect any serious pre-ignition, diesel sound, like I think I should. Then I just back it off about 10 degrees. I rebuilt the stock quad carb, idle needles work good. Screwed them in till I noticed a change and then backed them out one turn. At idle you can smell the raw gas coming out, but when your driving and open a window, if I have the timing a little retarded is smells like rich carbon exhaust, if I move the timing way up its about the same but even makes your eyes burn. If the ignition timing was even close, I would sum all that to the staion wagon effect.
     
  5. BIGBIRD

    BIGBIRD Registered Member

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    Thanks,
    I'll try that vacuum idea, that might tell me a lot about what's going on.. I guess I'll pull the balancer and have a look. I think It's just a standard 8". Friend of mine has heard of them slipping at the rubber joint. I thought that the balancer might be the wrong one but motor and heads are supposedly out of a '72 Z-28 so whichever balancer they used, '72 or '75 I think they're the same. In talking with the guy that built it, could be that if he really thought you couldn't time the engine with a timing light he never put the key in the crank when installing the ballancer. What about a wipped out cam ? Could that make you change your timing this much to make it run.
     

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