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the air/fuel mixture gauge

Discussion in '1969-1972 K5 Blazer | Truck | Suburban' started by ed rex, Sep 16, 2002.

  1. ed rex

    ed rex Registered Member

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    So, finally installed my Nordskog (analog) A/F mixture gauge. Setup was fairly easy, heated O2 sensor threaded into the exhaust pipe where the four header pipes come together.

    Problem is it's always pegged out 'RICH'. I suppose it backs off from pegged rich a wee bit if I'm performing a very fast decelleration down a steep hill, but other than that....at idle through WOT, it's pegged. Was wondering what other's gauges are like?

    The engine does however, run rich, but I didn't think that it would be 'off the scale' rich. Maybe that's where it's suppose to be gauge-wise? In any event, is re-jetting with smaller jets the only way to lean the motor out running? Should I lean it out at idle according to the new A/F gauge, then re-jet pending the results?

    Truck setup is: 454 w/75K miles. Edelbrock Performer intake. Holley 4150 series 750 double pumper. Headers. TH350.

    Is this too much carb for this setup? I have been back and forth between this carb and a Holley 600 single pump, but the 600 just doesn't give the desired uuuummmpppphh that the 750 does. Huge difference in acceleration 'feel'.

    Thanks!
     
  2. jc71355

    jc71355 1/2 ton status

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    Have you adjusted the mixture on each side of the carb. If I remember correctly these will lean or richen your motor. If everything is hooked up correctly (all connections sodered) and you don't have any exhaust leaks before the sensor I would definately tune with the guage. It's you best bet at getting it right IMO. How do you like the guage? I have looked at getting one of those for my '72 but that is farther down the list in things to do. I can't stress enough to soder those connections. I used a double crimp in my 91 with headers and I continually got lean errors. I thought it was exhaust leaks and I sill have a little but I sodered the connections where I had to lengthen the O2 Wire and since I've only gotten two lean codes in probably a month, which is many many times better than what I used to get (5-10 a day).
     
  3. ed rex

    ed rex Registered Member

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    I've attempted to adjust the A/F mixture screws on the side (primary & secondary, 4 total). I was however under the impression that these screws adjust for the idle a/f ratio? And that in order to adjust 'running' a/f ratio, you need to re-jet. True? In any event, it would appear that adjusting the idle a/f ratio produces best results when it's rich. If I adjust it to 'stoich', then the thing runs like crap! Also, the relationship of primary to secondary a/f mix (it's a double pumper) seems to be very key as well. Like if the primary is turned all the way out, the secondary needs to be all the way in. Right now, I have it so that all 4 are relatively evenly turned, and it runs rich with 'vibration' felt around the 2000RPM area. Any suggestions?

    I DO like the analog gauge. Not only does it have cool red night illumination, it's easy to read as the needle doesn't hop around, leastwise not on mine as it's always bent around the rich pin. I have mine mounted in the bezel, in one of the lower 2" spots. I will likewise take your advice and solder the connections. Currently crimped.
     
  4. lizard

    lizard 1/2 ton status

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    That A/F meter you have most likely uses a narrow band O2 sensor which works like an on / off switch. Unless it cost $1000+ and uses a wideband O2 sensor.

    It is kinda hard to tune with a narrow band O2 and carb since it will be nearly impossible to maintain stoich across the rpm band. I suggest you purchase a jet set, some new plugs and start hacking - that is read the plugs and tune from there!!! Your A/F meter might help get you pointed in the right direction. You are gonna need to run a little rich for best performance anyway...
     
  5. Robin

    Robin 1/2 ton status

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    There's some pretty good info @ GagetSeller .
    From that, I've deduced that for carb engines your going to have to pick where (in the rpm range) you want your stoich tuned to. I'd suggest your normal cruising speed (3000 rpm). WOT will likely alway be rich. I'm thinking of just wiring up a digital volt meter with a 2V scale to do this.

    It's very important that you don't go too lean (think holes in pistons), so favor the rich side.

    To change the running mixture, you'll need to swap jets, which are located inside the fuel bowels. Get a Holley carb book from Summit Racing, if you really care to optimize your A/F.
     
  6. K85 Octane

    K85 Octane Tacklin' Fuel Premium Member GMOTM Winner

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    I'm bringing this back.
    I'm in the same boat right now. I've been looking at running an Autometer gauge but don't have room for it in the dash. I also don't need to see it after the carb has been tuned. So I've also been looking at the FAST systems:
    http://www.summitracing.com/parts/FST-170401/
    http://www.summitracing.com/parts/FST-170402/

    I don't really know much about these systems or which one is best for me. I don't need dual sensors, I just need a method that's more precise when tuning the truck. It's either this, or take it to a dyno tuner thats local to me.

    opinions?
     
  7. K85 Octane

    K85 Octane Tacklin' Fuel Premium Member GMOTM Winner

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    from Scuba_Steve in an older post. Interesting stuff. And whoever posted this link about tuning. Scroll down some:
    http://www.bob2000.com/carb.htm
     

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