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Technical Timing Trouble with a SBC 350

Discussion in 'Traditional Hot Rods' started by showpony, Jun 14, 2017.

  1. showpony
    Joined: Apr 25, 2017
    Posts: 13

    showpony

    Hi all. New to the community and to car building in general. I have a 1949 Ford Club Coupe that has a 1972(?) Small Block Chevy 350 and TH350 transmission. Right now, I'm having trouble with timing.

    After reading this forum for days, I've learned a TON from all of you. I know that SBC's "like" about 12 degrees BTDC initial timing and you should end up with a total timing of about 35 degrees BTDC, without the vacuum advance hooked up. By 2500 - 3000 RPM, the full amount of mechanical advance should be in showing you your total timing.

    Here's the problem that I am having. When I set my initial timing at 12 degrees BTDC, my idle speed is around 1400 RPM. There's no room to lower the idle on the carb so to get it to my desired idle speed of 700 - 800 RPM, I need to move the distributor clockwise to get the RPM's to where I need them to be. When I do this and then hit the timing tape with the timing light, the 0 degree setting on the damper timing tape is, well, somewhere else, not registering any numbers on the tape. All I see is bare damper. Because of this, I don't have a start point for my initial idle speed, nor does a number show up when I rev the engine to 3k RPM or wherever the timing stops advancing to find the total timing.

    It should be noted that I (the rookie) was the one that had to find TDC on the #1 cylinder and add the timing tape to the correct spot on the damper. With this initial setting, it did allow the car to turn over and run, but I'm stuck with not being able to time it because of what can only be described as a misplaced timing tape. But I don't think this is what the problem is. I'm reluctant to even check for TDC on #1 again because I went through the procedure for setting TDC like 4 times, to make sure it was right. Coupled with the fact that this initial setting made the engine run pretty well too is making me think this is something else than that. But, like I said, I'm a rookie at this and I'm looking to figure out where I went wrong. I'm hoping someone here can provide me with the correct insight into this. If you need more info, please ask. Thank you!
     
    Last edited: Jun 14, 2017
  2. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    Are you setting the timing at idle, with the vacuum advance line disconnected, and plugged, transmission in drive, and idle set?
     
    54vicky likes this.
  3. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    Oh, and what carburetor is on this, and have you checked for vacuum leaks?
     
  4. lippy
    Joined: Sep 27, 2006
    Posts: 4,317

    lippy
    Member
    from Ks

    How did you find exactly TDC? Lippy
     
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  5. Terrible80
    Joined: Oct 1, 2010
    Posts: 730

    Terrible80
    ALLIANCE MEMBER

    You should be able to lower your idle to the point the car dies.
     
    Truck64 likes this.
  6. showpony
    Joined: Apr 25, 2017
    Posts: 13

    showpony

    I did the method where you screw a fitting into the #1 plug hole and through that adapter is another threaded section that allows for an internal threaded rod to be used as a stop for the piston. Rotate the engine clockwise slowly until you hit that stop you threaded into the #1 cyl. Mark this line on your damper at 0 degrees. Rotate the engine counterclockwise very slowly until the piston travels down and then back up to meet the stop threaded into the cyl and mark this other stop point on the damper. Depending on how far down the cyl #1 the stop was, you may have two marks pretty close to one another. The center distance between these two marks should in theory be TDC.
     
    Last edited: Jun 14, 2017
    Engine man and pat59 like this.
  7. showpony
    Joined: Apr 25, 2017
    Posts: 13

    showpony

    Lower on the carb or on the rotation of the distributor? I tried it on my carb but there was no adjustment left to lower the idle. The only way to get the idle where I wanted it was to rotate the distributor clockwise. Rotate it far enough and yes the engine stalls.
     
  8. showpony
    Joined: Apr 25, 2017
    Posts: 13

    showpony

    I am setting the idle first but I'm only able to achieve my desired idle by rotating the distributor clockwise (retard?). The vacuum advance line is disconnected and plugged. I've never heard of setting timing with the transmission engaged. Is this something you are supposed to do that would require an extra person to hold the brake while the trans is engaged? All the videos I watched on this subject, the timing was set while the vehicle was in park to find your total timing.
     
  9. Dick Stevens
    Joined: Aug 7, 2012
    Posts: 2,721

    Dick Stevens
    Member

    You don't need it to be in drive to check timing, I suspect you have a vacuum leak causing too fast idle speed.
     
    jeffd1988 likes this.
  10. showpony
    Joined: Apr 25, 2017
    Posts: 13

    showpony

    Sorry. The carb is an Edelbrock 650 cfm Performer series
     
  11. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    If you can't lower idle on the carb, you may have other issues.
     
  12. showpony
    Joined: Apr 25, 2017
    Posts: 13

    showpony

    Dick, the more I think about it, the more this makes sense. Now how the F^#@! do I track down a vacuum leak like this one? I guess I'll stand over the engine tonight for a few hours and look at hoses, caps, cracks, looseness in carb mount, etc. Any other usual suspects you have as some favorites to check?
     
  13. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 2,012

    2OLD2FAST
    Member
    from illinois

    Either you have a linkage problem [something not allowing the flaps to close completley] or a vacuum leak [I've had good luck w/ a peice of 3/8 fuel hose asa stethoscope to listen for a hiss]
     
  14. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    Well, which manifold is that Edelbrock on? You can bolt a square bore Edelbrock to a spread bore manifold (and some combo spread/square bore manifolds), bit it will not seal, without the thin plate, and two gaskets designed to prevent that exact leak.


    I would wager that every single one of the members of this board, that has installed a gasket, has had one just not quite seal. It happens.

    If you have power brakes, disconnect that hose on the booster, and plug it, to see if you have a booster leak.

    You can try spraying a little starting fluid, or carb cleaner around sealing areas, while the engine is running. If the idle speeds up, look there. Don't over-do it and start a fire.
     
  15. showpony
    Joined: Apr 25, 2017
    Posts: 13

    showpony

    I will have to go back over the exact part numbers of intake and the plate/2 gaskets, but It's an Edelbrock Performer Carb and Performer Air Gap Intake. I don't have the exact part numbers for you right now, but I will post them later when I get home.
     
  16. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    I always set them in drive, with the idle speed properly set.

    No-load idle is not an accurate or meaningful place to set timing. You cannot drive the car like that.
     
  17. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    It's probably a fine match in terms of components. Just make sure that any unused ports for vacuum are capped, and if you are not using the one in the back, that it has a plug in it.
     
  18. DDDenny
    Joined: Feb 6, 2015
    Posts: 13,093

    DDDenny
    Member
    from oregon

    Welcome and extra credt for being so articulate in your descriptions, we rarely get that, much easier to help when we have this much information.
    Never had a problem finding tdc using the finger in #1 hole and having helper bump starter over. Just to be sure, #1 is right side front facing engine, but you knew that.
    Are you sourcing vacuum from above or below throttle blades?
    Is there a bolt-on timing pointer on the timing cover or the spot welded version?
    These should be plenty dependable for the average street engine as long as they match the correct keyway location on the harmonic balancer.


    This vvvvv

     
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  19. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    ^^^^This^^^^. This is an excellent point.

    If the engine has been gone through, and you don't know the history, there could be a parts mismatch.

    GM moved the timing pointer, thee times, over about a 40º range. It all bolts together, but you could easily end up with a timing mark/pointer misalignment. Toss in some aftermarket parts, and who knows what exactly could be going on.

    [​IMG]
     
    tfeverfred likes this.
  20. I'm guessing vac leak also. Is the motor warmed up and the electric choke set right?
     
  21. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    X2 on this. Normally, we have to extract about every little detail, one post at-a-time.

    Clarity is king. Thank you!
     
    Flatblack 31 likes this.
  22. phoenix5x
    Joined: Dec 26, 2007
    Posts: 219

    phoenix5x
    Member
    from Ohio

    Like gimpsy said..spray around the engine..What I thought was a vacuum leak once was actually an intake gasket that hadnt completely sealed on the intake runner...so spray around the intake to head surface too..just lightly like he said dont over do it. I also saw you said you had no more room to rotate the distributor. Is this due to a physical restriction in the engine compartment? I have sometimes also had to try and lift the distributor up and try and drop it in 1 or 2 teeth over from what I thought was actual TDC to allow me a little extra room to regard the timing...I would try this if you find no vacuum or gasket leaks.

    Sent from my VS995 using The H.A.M.B. mobile app
     
  23. bonzo-1
    Joined: Oct 13, 2010
    Posts: 328

    bonzo-1
    Member

    Make sure the choke high idle cam is not holding the throttle open.
     
    54vicky likes this.
  24. Russco
    Joined: Nov 27, 2005
    Posts: 4,087

    Russco
    Member
    from Central IL

    I assume you have the vacuum ports on the carb capped off?
     
  25. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,796

    tfeverfred
    Member

    I've run into this a few times and it was a nightmare, until we figured out what was happening.
     
  26. Black Panther
    Joined: Jan 6, 2010
    Posts: 1,520

    Black Panther
    Member
    from SoCal

    Are you running a throttle rod or cable? Either way you should be able to adjust the idle down as others have said...look at the idle screw...is it touching the linkage arm on the carb like it's supposed to? In other words...is the idle tang on the carb arm resting on the screw? I'd disconnect the linkage and see if you don't have enough travel in your accelerator linkage. Disconnect it and see if the idle screw does something then....
     
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  27. gimpyshotrods
    Joined: May 20, 2009
    Posts: 16,581

    gimpyshotrods
    Member

    Also, make sure that the idle tang is not bent, propping the throttle open.

    [​IMG]
     
  28. BJR
    Joined: Mar 11, 2005
    Posts: 6,105

    BJR
    Member

    When you say you plugged the vacuum advance, did you unplug it at the carb and plug the port on the carb or did you unplug it at the carb and plug the hose? The carb needs the port plugged not the vacuum advance. Just checking.
     
    54vicky likes this.
  29. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    TDC in relation to the timing plate on the engine was determined by the piston stop method so it doesn't matter which timing plate is on the engine.

    At 1400 rpm the centrifugal advance is probably already advancing the timing. You need to get the idle down.
     
    54vicky likes this.
  30. Disconnect linkage. Back off all idle screws. Hold a couple fingers over the carb primaries, like you're choking it . If it doesn't try to stall, you've got a big time vacuum leak. Most likely at the mounting flange.
     
    jeffd1988 likes this.

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