1. Anthony 71 Paisley

    Anthony 71 Paisley Member FCBO Gold Member

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    Good morning all, just curious how long you should run a plug before you try and get some information on whether it's burning lean or hot fouling Etc. I see some people say they take it for a 2-mile ride up the road pull the plugs and make adjustments. Is that enough time? Should it be 50 miles 200 miles? The reason I ask is my new 360 I have a 600 carb on it and it seems to be running lean. I jetted it up and I'm curious how long I should let it run before I make more adjustments.
     
  2. CBODY67

    CBODY67 Senior Member

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    Just curious, what gives you the impression that it's "lean"? What carb number? What main jets? What timing curve? What spark plugs? What rpm range? What engine condition and oil consumption?

    As for reading the plugs for a normal street car, I'd favor probably a good consistent highway run and then look at them after a tank of gas, provided the jet sizings are close to what the OEM carbs Chrysler used in a similar carb on a similar-sized (CID) engine.

    Ultimately, getting the car onto a chassis dyno for some "road load cruise" testing might be quicker and more accurate. Most allow about three pulls within a particular span of time, but after the first pull/time, the a/f readings would be there immediately.

    OR if you can find a shop with a Sunn engine analyzer which will test emissions gasses and air/fuel ratios in a no-load situation, that would work too, for what you're seeking. See what it shows at 2500rpm.

    Just some thoughts,
    CBODY67
     
  3. Anthony 71 Paisley

    Anthony 71 Paisley Member FCBO Gold Member

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    I'm running an Edelbrock 1406. Stock was .097 (I believe) I went to .101 . Running Autolite AP65. Right now I'm at 8 degrees initial to 30 total all in by 2k. I backed off , because I have been noticing what i thought was a ping but now I think it's a misfire. I'm going to a colder plug (tommorow) and replacing cap and homemade wires (hopefully after work today). Not burning any oil.

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  4. 413

    413 Active Member

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    Emission analyzer is a great tool. But doing an unloaded test at 2500 RPM tells you exactly nothing about your jetting. You need a loaded test for that.
     
  5. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    Last edited: Sep 10, 2019
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  6. Turboomni

    Turboomni Senior Member

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    You could go the wideband band O2 sensor route.
     
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  7. CBODY67

    CBODY67 Senior Member

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    With the Edelbrock and any other "metering rod" carburetor, you have to figure in the various diameters of the metering rods, too. The 'economy" (larger, toward the top) and the "power" (smaller, toward the bottom) diameters. Those plus the jet sizes and the "power valve spring" tension makes the calibration for the primary side of the carb.

    The "road load" and "unloaded" test at 2500rpm would give you the "economy" side of things, being that the engine manifold vacuum should be above about 17" Hg. "Road Load" would simulate what the engine would be at during a level-road highway cruise event. So no matter whether "road load" or "unloaded", the vacuum level should be high enough for the vacuum advance in the distributor to be maxed-out, with a total advance (vacuum + centrifugal + base timing) at this part-throttle situation near 50 degrees BTDC.

    The "loaded" situation would have enough load to put the intake manifold vacuum close to about 5" Hg, which would most probably be WOT. THAT'S when the 38 degrees (or a bit different for an LA motor) figure would be operative (centrifugal + initial base timing). Just to clarify things.

    How many miles are on the plugs? They look new, from what I can see from the pictures. A "leaner" mixture would keep the insulators "white", but when the mixture is too lean, it becomes a chalky white, rather than a smooth white.

    When plug reading was discussed back in the '60s, the racers had a special viewer/light that they used to look at the base of the insulator, rather than just the exposed tip.

    On my various 383s, the 2bbls spec'd Champion J-14Y, the 4bbl spec'd Champion J-10Y. The '72 400 spec'd J-13Ys. In normal daily driving, they'd all have a light tan/white insulator tip. With their stock jetting. The 360 had something like a "9" or "11 heat range Champion, I believe. Not sure how the heat range of your plugs relates to that, but as long as they are spec'd for it, whatever works.

    Once, I was trying to better adjust the idle mixture on one of my cars. I'd put an OEM-spec Holley on it with a Holley Z-Line intake, with a slight cam upgrade. I had it hooked up to the BIG Sunn diagnostic roll-around we had in the shop back then. I was trying to get the CO down to what they claimed it should be, BUT when I got close, the idle got a little shakey and the digital HC readout went nuts. I'd hit "lean misfire". Not a real "miss" but not a full "hit" either. As soon as I rickened it back to where it was, the readings settled down to normal. So, "lean misfire" is not the same as a bad plug wire miss, or similar.

    My own personal theory of plug heat ranges is to use the equivalent of the OEM heat range in whatever brand you like. BUT if you want to add a bit more advance into the mix, then going one heat range colder might be advisable. Which would keep the insulator tip a bit cooler with better combustion heat dissipation through the spark plug body.

    Keep us posted on your progress,
    CBODY67
     
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  8. Anthony 71 Paisley

    Anthony 71 Paisley Member FCBO Gold Member

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    Thanks all ,the plugs have around 300 miles on them ... I started with the Edelbrock 750 it felt a little doggish so I dropped it to the 600. The 600 ran like garbage as there was a tiny piece of what looked like speaker foam in it. It came out when we blew some compressed air through it on the bench. I have been running the 600 for about 200 miles. The fouling on the plugs I would say was probably when the 600 was just installed . Last night I put in NGK BRP8ES which apparently is 2 heat ranges colder. & new duralast wires ( eliminating the Homemade MSD wires) . Currently I have vac advance disconnected ( I wanted to eliminate that as well )I'll fill it up tonight and take it for a spin and see if any change
     
    Last edited: Sep 11, 2019
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  9. furious70

    furious70 Active Member

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    Generally you put fresh plugs in and then immediately go operate in the range you want data for and shut off to examine immediately after. Cruising around for 200mi is just going to give you an average of what's happening. It can show detonation, can show generally if your timing is right by where the burn is on the arc, etc.
     
    Last edited: Sep 11, 2019
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