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Fixed my rough warm-up problem (FYI)

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blue85b, Mar 5, 2001.

  1. Blue85b

    Blue85b Registered Member

    Mar 5, 2001
    Likes Received:
    I have had a problem this winter with the truck running rough until it was warmed up. So I looked into the choke. My Q-Jet is set up with a rear "vacuum break" (this part is mis-named, but oh well..), but no front vacuum break and an electric choke. When you first tap the throtlle, the choke plate closes all the way to supply super rich mixture for starting (since most of the gas liquifies in the manifold anyway). When the engine starts, vacuum pulls on the rear vacuum break and it pulls the choke open slightly to lean it out from starting mixture (8:1?) to cold running mixture (12:1?). As your vacuum drops (opening the throttle), the vacuum break relaxes and the choke closes more, richening it up. All the while, the electric choke is warming and it's coil is slowly opening the choke up, so that the mixture continues to lean to about 14.7:1 when the engine is at normal operating temperature.

    What my ride was doing was to start good, idle nice for about 5 seconds and then start to sputter a little and blow some black. This would continue for a minute or two, after which the idle speed would come up and it would idle great. Obviously it was either running rich or had ignition problems. HEI problems are usually worse on a warm engine, so I turned to the choke. I bent the little rod that connects the vacuum break to the choke to shorten it up. This leans it out just after starting, until the coil starts takes over. Runs nice now and I no longer have to warm the thing up before I take it out. Just thought that this might help somebody else out.

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