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post #1 of 3 (permalink) Old 02-03-2009, 09:19 AM Thread Starter
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Read your plugs to determine mixture

Found a good tutorial on plug reading. Pretty informative!!

Reading Spark Plugs

2011 Teryx Sport
2011 50" STD RZR LE
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post #2 of 3 (permalink) Old 02-03-2009, 10:24 AM
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Great info.

Everyone should learn how to read their plugs. I worked for 5 years at ACCEL DFI doing tech support and training for the DFI programmable EFI systems. One of the most common mistakes people made was relying exclusively on an oxygen sensor for tuning.

I hear this even today - "You need an oxygen sensor and dyno to tune EFI" - well that's not absolutely true. Anyone telling you this doesn't really understand EFI, or they're selling oxygen sensors. Sure an oxygen sensor and a dyno make it easier, but it's not required.

Working on engine development projects, you rely on the best engine dynos (not chassis dynos) with the latest data logging equipment (far exceeding a wide-band oxygen sensor). This equipment is maintained and calibrated on a regular basis. Why - well that's the only way to get reliable data. Experienced dyno opertaors use the gauges, but will also take the time to read the plugs.

The best first-time EFI tuners that I spoke to at DFI were old-time racers. They'd say, "I don't know anything about computers, but I've been jetting carbs and reading plugs for 30+ years." This made thing easy, as these guys already knew how to tune an engine, they just needed to learn to use a computer instead of a jet wrench.

The absolute worst first-time EFI tuners that I spoke to were IT guys or electrical engineers who had no experience tuning an engine. These were the guys that expected the computer and sensors to tell them what to do.

So, back to the subject: I'd strongly recommend that everyone modifying their carb or EFI engine (even pipes and other common bolt-ons) should learn to read their plugs. Go out and run it wide open, kill the ignition, coast to a stop and read the plugs. As I was told many years ago by an well respected dyno operator "Yeah, I know what the gauges say. Now get in there and read the plugs! The plugs don't lie." Yeah, he was kinda crabby , but he knew his stuff .

Last edited by Thunderhawk; 02-03-2009 at 01:07 PM.
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post #3 of 3 (permalink) Old 02-03-2009, 06:04 PM
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Then tell me how to do it since we don't have leaded fuel and we can't turn our engine off and push in the clutch capturing the plug in the right state?

By reading a plug in a CVT vehicle the piston will pull fuel in on decel and change the look of the plug making it look richer than it really is.

Think I will stick with the air/fuel ratio myself, I'm a computer geek though.

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