Via the formula racing team, I learned that an aftermarket free-flowing exhaust will make an engine run lean. Our dyno bike went from 1 lambda on stock exhaust to 14 lambda with our exhaust, on a carburetor.

This made me think about my Go-cart that i'm trying to sell... It has an open header, and I'm wondering if I need to re-jet it to keep from grenating the motor (it has probably 100-150 hours with the header). I read that most O2's read half a volt at a lambda of 1, so what would I have to do to get an accurate A/F ratio indication to see if it needs re-jetting?

It tops out at 45 MPH, it has 22" tires and a 6.70 chain ratio with a 1:1 max CVT.

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Open exhaust may lean out the system but not that much as to change the jets. You should have adjustment screws for the mixture. Just adjust that.

 

Like i said, on our dyno bike we went from stock exhaust to our straight through exhaust (on a 250 single) and it went from 1 lambda to 14 lambda. so, i'm not sure... hence I'm asking what it would take to ge an estimated O2 reading. We had to go up 3 sizes on the bike's jets (went from stock to a 3" pipe and titanium muffler 12"x5").

 

I read a couple articles, so an O2 operates over 600 degrees F and can be bench tested by recording the voltage between the output lead and the casing.....

did I understand it right?

edit: found these

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What is lambda?

 

http://en.wikipedia.org/wiki/Air-fuel_ratio#Lambda

^^ for the not-so-engineeringly minded here.

 

Okay. I may not be an automotive engineer, And I am sure your not. I am a ASE certified master mechanic, though it is not my profession.

 

no, i just have my head in the formula racing club we don't use AFR at all...everything is in metrics and lambdas.

a better link: http://www.hondata.com/techlambda.html

table on right: http://www.techedge.com.au/vehicle/wbo2/wblambda.htm

1 lambda = 14.7:1 A:F ratio

so our bike dyno was in the 150-200:1 AFR range with the open pipe...hence having to go up three jet sizes and being 10 HP off of the stock number (24 HP mod vs 34 HP stock)

 

So I'm thinking- could I put a voltmeter on the O2 sensor on my truck while it's warmed up and running to see where the truck ECU has 1 lambda at voltage-wise, then remove it from my truck and set it next to the exhaust stream of my go-cart and see what voltage I get then and go from there?

 

the engine is a Tecumseh HM80-155678S per the riverted serial badge. But I can't find any information on this specific engine model, only the HM80. The carb says "516" on the side but that seems typical for all.... I don't see any obviously adjustable screws except for the idle speed screw. There's a bolt on bottom of the bowl, apparently on the newer carbs this is an adjustable jet screw, but I think on mine, it's simply the bolt that holds the bowl on the carb.

Also, I know it is lean, because it will only start on starting fluid unless I pull the start cord 20 or 30 times, with choke full closed and throttle 1/4 open either way.




Above and below, I think these are the micture screws maybe??? I stuck an allen in them and didn't feel anything...?