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Help! "New" Truck

Discussion in 'Chevy Trucks' started by 76GMCK15, Jun 21, 2003.

  1. 76GMCK15

    76GMCK15 Junior Member
    Messages: 3

    I’m new to this forum and to turning wrenches. I just bought a 76 GMC K15 with a 350 4bbl (cali emissions, 4mv carb). It is not running well, to say the least, and barely made it home. My question is as follows. The hose coming from the throttle return control valve that goes to the carb is not connected and looks like it has been free for a long time. I think that the hose from the vacuum unit on the distributor is connected to the carb where the throttle return control valve hose should connect. This connection is directly above the fuel pipe connection on the carb. Second related problem: there is a plugged inlet on the front of the carb just below the throttle level actuator bracket. So, does the hose from the distributor go on this inlet, or …

    Any help would be greatly appreciated.
  2. Clemens

    Clemens Junior Member
    from Europe
    Messages: 9

    hey, try to get a shop manual (haynes or chiltons, or better yet, get both) and see if they have some vaccum diagrams in there...
  3. Arc Burn

    Arc Burn PlowSite.com Addict
    Messages: 1,141

    Welcome to the site,we have a handfull of gearheads here that can answer your question in a heartbeat but this site gets slow in the summer,be patient,they check in a couple times a week.If your in a hurry,i would PM Wyldman,good guy and knows his stuff:waving:
  4. wyldman

    wyldman Member
    Messages: 3,265

    Welcome to Plowsite.

    Not to familiar with California emission stuff,as we don't se them here,but I can help you sort some of it out.

    You will need a vacuum gauge to find ported and constant vacuum sources,and the timing of those ports.

    The distributor vacuum advance normally goes to ported vacuum,which comes in just off idle.So you would not see vaccum at that port,unless you just slightly crack the throttle.

    The EGR vacuum usually hooks up to a later ported vacuum,which comes in a little further off idle,and pulls less HG's of vacuum.It will run from the carb,through a temp vac switch in the t-stat housing and to the EGR valve.

    The thermostatically controlled air cleaner door,is routed from constant vacuum,through a temp vacuum bleed switch,to the heat riser door.

    I would disconnect all the throttle return control valve crap,and set your base idle manually,and start from there.

    Another good idea would be to chuck the California emission Rochestor Quadra-jet,and get a good aftermarket replacement,like an Edelbrock,or a Holley.Many of these have California exemption numbers to pass emissions.

    BTW - Thanks for the kind words again Arc :salute:
  5. 76GMCK15

    76GMCK15 Junior Member
    Messages: 3

    Wow! Thanks for the info Wyldman and Arc Burn. It will take me some time to digest your information. I'll keep you all posted. Thanks again.
  6. wyldman

    wyldman Member
    Messages: 3,265

    Any luck with your truck yet ?
  7. 76GMCK15

    76GMCK15 Junior Member
    Messages: 3

    Well...Kinda. The hoses were in the wrong places, according to my vacuum results and the vacuum diagrams I have found. But, that problem was just the tip of the iceburg and I could write a long list. The problem I am addressing first is the fact that the secondary cam lockout lever is missing and trying to figure out how the mechanisms of the carb work. As far as the carb mechanisms go, I'm stuck on the fast idle cam position, after the engine is warm and turned off. The cam is "locked" into position in a way that the choke lever is holding the choke open and even when the engine is cooled down, the choke valve is held open. The cam can be manually rotated in a counterclockwise position so the choke valve will close. Anyway...that's were I'm at. Any words of wisdom? Oh yeah...I found a rochester 4mv at the junk yard (25 bucks...could not pass it up) that is from a 350 4bbl automatic transmission van (G30) of the same year my truck is. Could this work in my truck (after a rebuild)? Just wondering...if anything it will be interesting taking it apart. Sorry for the long post.
  8. wyldman

    wyldman Member
    Messages: 3,265

    When you try to get the choke to close are you opening the throttle slightly ? It must be opened to allow the choke to close and the fast idle cam to clear the fast idle screw.

    It's also possible someone cranked the choke cap way off,so it won't allow the choke to close ? Maybe the cap is bad,and that's why it was done ?