[Chevelle-list] : OT - GMC TRUCK HELP

[Clyde]

Hello:did the truck doe this before the new carb?.If so there is a possibility the float level is low or the power valve is seized.check these out and let me know.
  ----- Original Message ----- 
  From: Larry Shouse 
  To: The Chevelle Mailing List 
  Sent: Wednesday, September 12, 2007 5:25 AM
  Subject: *****SPAM***** Re: [Chevelle-list] OT - GMC TRUCK HELP


  Clyde,

  The original air cleaner is long gone. It now has a 9 inch round by 3 inch tall K&N filter on it. The air filter has no ppes or lines going to it. I have oe vacuum line going from the carb (the one facing forward) going to the distributor, and that's it.  I will look into the choke pulloff, etc.

  Thaks,
  Larry Shouse


  ----- Original Message ----
  From: Clyde <ntauto at csolve.net>
  To: The Chevelle Mailing List <chevelle-list at chevelles.net>
  Sent: Wednesday, September 12, 2007 5:16:42 AM
  Subject: Re: [Chevelle-list] OT - GMC TRUCK HELP


  Hello:first off make shure the pipe from the exhaust manifold to the air cleaner is intact,also check to see if the little flap opens up when the engine is started cold.if not that must be fixed.H ow does the truck start when cold?does it start and stall?.On your cold start check and verify the choke pulloff is working as it should.There is a possibility that when you start to drive the choke pulloff is starting to close up,causing a rich condition(black smoke).The choke pulloff migh t be adjustible(set screw in the rear of the diaphram or on the side),some of them you have to bend the rod.If the flap in the air cleaner is not working,there is a possibility that the thermo vac switch that controls it is tired.If it is you maybe able to find another one or you can find another vac source to make it work.Give these a try and let me know,if i can help in any other way Clyde.   
    ----- Original Message ----- 
    From: Larry Shouse 
    To: The Chevelle Mailing List 
    Sent: Tuesday, September 11, 2007 7:18 PM
    Subject: Re: [Chevelle-list] OT - GMC TRUCK HELP


    Thanks for your reply Brad. Yes, a half ton.

    The carb is an Auto Zone rebuilt that I recently installed. I replaced the points, plugs, wires, cap, rotor, condenser and coil. Of course new doesn't automatically equal good, but all items listed seems to be functional. Can an old and possibly degraded distributor cause this type of  symptom? The dwell is running at 31 degrees and steady, which should be close enough. When I rev it up with the timing light on, the mark climbs up and off the gauge so the advance curve at least starts off correctly... The plugs are running  gaps of 40. 

    As a youth, I was taught black smoke means to much fuel, which means not enough air or too much fuel at those RPMs.... Is there an adjustment for the fuel/air mixture off idle on these carbs?

    Larry Shouse

    ----- Original Message ----
    From: Brad Olson <bdo_chevy at att.net>
    To: The Chevelle Mailing List <chevelle-list at chevelles.net>
    Sent: Tuesday, September 11, 2007 6:31:31 PM
    Subject: Re: [Chevelle-list] OT - GMC TRUCK HELP


    -------------- Original message ----------------------
    From: Larry Shouse <lpshouse44 at yahoo.com>
    > I'm hoping some of you my be able to help with a couple of questions
    > I have concerning my 1970 GMC truck. It has a straight 6 250 CID
    > engine with a 3 speed manual tranny and a 1 barrel MonoJet carb.

    Half ton, right?  My dad had that very same truck from '72 to '85.
    The shift linkage went bad in the column and he converted it to a
    Hurst "Indy" floor shifter.  I used to take it out on the back roads,
    wind it up, pop the clutch, and the back end would bounce around
    like crazy.  ;^)

    > First question is on timing. My service manual says to refer to the sticker 
    > under the hood for timimg, but my sticker is long gone. I did find one of my old 
    > tune-up guides from the 70's that says on L6 Chevelles, it should be 0 degrees 
    > on automatics and 4 degrees BTDC on manual tranny vehicles... Should I go with 4 
    > degrees BTDC? Also, each mark on the timing guide by the flywheel on these 
    > things is 2 degrees right?

    Yes, the timing tabs are marked in 2-degree increments.

    I checked my Haynes book and it too defers to the underhood sticker.  4 BTDC
    is as good a place as any to start, and if it runs fine then try adding a
    little more advance until performance degrades.  If you use it more as a
    driver and less as a hauler the original factory specs may be allowing for
    some engine loading that your truck doesn't see.

    > Second question is on my carb. While accelerating normally, it starts to spit 
    > and sputter at around 2000 rpms, then clears up at around 2500 rpms or so. While 
    > it's doing this, I see black smoke coming out of the exhaust. Before and after 
    > this rpm range, my truck doesnt smoke. Well, it does at red line but that's gray 
    > smoke and I thing an entirely different issue with this tired old engine. Do you 
    > think in the 2000 to 2500 rpm range, it's getting too much fuel? If so, how do I 
    > fix it?

    Sounds like a carb issue, especially if it's been years since the Monojet's
    been gone through.  If possible, put a vacuum gauge on the engine and
    observe what it reads in the RPM range in question.  Is the rest of the ignition
    system up to snuff?

    Brad



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