I went looking for information on "reading" spark plugs to assist me in learning how to tune the carburetor on my chainsaw. From what I learned in the following video I am now wondering if it is applicable to improving the fuel economy in my truck.

What are your thoughts on the following video, only good for racing, or relevant to a daily driver as well? https://www.youtube.com/watch?v=MecCoercp-s

I would install a wide band o2 sensor and get the fuel mixture in the ballpark. The o2 sensor would show the average. Then start reading spark plugs to fine tune. But he is right, reading spark plugs only makes sense at the end of a drag stripe pass or on a dyno. And I guess it helps if you have a lathe to cut them apart. Otherwise you are no better off then just using an o2 sensor.

All of this only makes sense if you have a carburetor the you can actually tune.

Thanks kesteb, you make good sense.

I have a 1945 with a brass float. My plugs are a bit dark, and the truck gives a puff of grey smoke upon startup after a hot shutdown. Thinking I can check to see if my float is bit high.

Agreed that an O2 sensor is a good thing, and I already have one.. but I would like to wait until the Dutra duals are installed before having the O2 sensor nut welded into the exhaust.

Agreed - the wideband will tell you a lot more than spark plugs. (A narrow band O2 sensor can get you some useful info on fuel economy, but not nearly as much.) The one thing reading the plugs can do that an O2 sensor can't is tell if individual cylinders have issues.

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Matt Cramer
1966 Dodge Dart turbo / EFI project

I have almost never seen differences between plugs on a Slant 6 and the distribution is quite even on a well tuned/adjusted engine. WBO2 sensor is your best bet for sure.

Lou

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Home of Slant6-powered fun machines since 1988

Ok, How close to the manifold does the wide band O2 sensor need to go? Maybe I can find a place that will allow the front of the Dutra duals to join in a place that does not interfere with O2 sensor.

It should be something like 12" or more beyond the head port exit so it does not overheat. I put mine usually 18-24" past, just after my shorty header collector. For Dutras, I would put it on the front bank about 10 to 18" past the exit of the DD manifold. That should be easy to access but not get in the way of anything. You can weld the bung on the top of the pipe or on the side, but not on the bottom so there is no water collection/drainage issue.

Lou

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Home of Slant6-powered fun machines since 1988