timing issues

Discussion in 'General Chevy & GM Tech Questions' started by jkel09, Dec 26, 2010.

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  1. jkel09

    jkel09 New Member

    i have a 1985 s-10 blazer that i put a 267 v8 out of a 79 malibu into. i am having trouble getting my timing set as too every reference i look up gives me different specs. i am curious at to what the actual spec for the 267 in 1979 would be and also what end of the vacuum hose do i plug off when i remove it from the vacuum advance to set timing. my goal with the truck is to optimize mpg rather than power and speed. i recently installed a summit ignition box and lost about 2 mpg which i dont quite understand why. i put the condensor back in and am going to run some tests to see if this improves my mpg. i have installed new plugs,wires,coil,cap,rotor,fuel filter,fuel pump, and i intend on droping from a 650 cfm carb to 500 cfm. i would like to reinstall the ignition box but not if its going to decrease fuel economy(which i was told would actualy increase mpg). after installing all the new parts and making adjustments i actually lost mpg which i find rather odd because through the mountains on my trip down i was getting better mpg than i did once i hit the flatlands. i am rather confused by all this atm so any advise you may be able to offer would be greatly appreaciated.
  2. stephan

    stephan New Member 1000 Posts 100 Posts

    Hey JK welcome to the GM club. Is your Summit ignition box a multiple discharge ignition box? Describe exactly which box you have.
    As far as the timing, you should disconnect the vac hose from the dist advance pot & plug it with a golf t or a screw (whatever's handy) If you disconnect the other end then you just have to get another piece of hose to plug the port & the end of the hose too so it is just easier to disconnect at the dist.
    For your initial timing setting (@ the crank) try between 8 & 12 degrees advanced. If it pings on acceleration retard it. If it cranks slow, also retard it. The key for mpg is more advance, but not if you suffer either of these 2 maladies. You will want about 10 to 15 degrees of mechanical advance, but if you don't want to mess with it, just make sure it is free & not binding & go with the stock mechanical. Also if you have a dial back light so you can check the total advance, you will want 40 to 45 degrees.
  3. mfleetwood

    mfleetwood Moderator 1000 Posts 100 Posts

    Welcome to the Club!! You're in good hands with Stephan......
  4. jkel09

    jkel09 New Member

    thank you for the warm welcome. i have been searching for a good site for some time and am glad to have found this one. as for the box it is a summit racing street and strip digital cd ignition box. part no. sum-850610 (though i dont see anything digital on it) i do not have a adjustable timing light either.right now i believe im at 12 btdc but that is by taking the vacuum line off at the carb that leads to the advance and blocking that end. atm i am still doing milage tests with the original condensor back in the dist.
  5. stephan

    stephan New Member 1000 Posts 100 Posts

    12 degrees initial is good, but you need to beg, borrow, steal, or buy a dialback timing light so you can check your total advance (initial + mechanical + vacuum + total). You can't really check the total without it.

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