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What air fuel ratio's do you guys see when riding along the trail?

Octanee

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Hey guys, as the title says, what air fuel ratio's do you guys see along the trail? I have a new to me turbo pro and I noticed she likes to run lean on light cruising throttle/speed, anywhere from 14-17:1 air fuel, and a certain spot Itll hover closer to 17, it's outside of. Boost so I cannot add fuel. When I roll the throttle to start into the power it of course dips down, I shoot for 12:1 in boost just from my knowledge coming from a 4 stroke., what do you guys shoot for while in boost? there was a YouTube video of a trail rider with a a/f gauge put on and his ran lean the same way, however it had no description so I was unsure if that's because his had an issue or not?

Thanks!
 

TRS

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Where your sensor is located and what type of fuel you are running has a very definite effect on your afr reading. Not all sleds are created equal and must be tuned accordingly. We had this discussion a few years ago. You must read your plugs and piston wash to get an accurate reading and correlate that to what your afr reads. Same as you would do for EGT gauge readings. I know this isn’t what you want to hear, but there is not a simple answer. If you don’t have the expertise to tune it accordingly, please find someone that is competent. Your wallet will thank you for it, along with less frustration.
 

Octanee

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Thanks for the replies, the a/f sensor is located right after the turbo, approx 10 inches up from the outlet. It's an aem, the turbo kit is boost it with their xic fuel controller. I do understand plug color and piston wash, I do have a bore scope. I've ran approx 30% av and 70% 94 pump gas so far. Mainly I'm wondering out of boost trail riding what you guys are seeing? Id think it should be OK? Since it's our of boost, should be behaving like stock? Hmm
 
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sledhead9825

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I had a Boost-it Pro. On the trail a 15-17 AFR is pretty normal. Thats factory stock numbers . It concerned me at first but never a problem. Try not to look at the AFR gauge unless your at full throttle under load. Shoot for 12. 2 -12.4 and your all good.
 

Octanee

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I had a Boost-it Pro. On the trail a 15-17 AFR is pretty normal. Thats factory stock numbers . It concerned me at first but never a problem. Try not to look at the AFR gauge unless your at full throttle under load. Shoot for 12. 2 -12.4 and your all good.

Thanks for the info! I was thinking it's gotta be normal since it's out of boost, I know my fuel injectors are good, I had them out and checked.
 
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Like previously mentioned, AFR is just a number that depends on a lot of factors. Tuning a 2 stroke is not the same as a 4 stroke. 2 stokes are more sensitive to heat and thermal management. Therefore, a best practice is to enrich the fueling until the sled starts to misfire and sputter at WOT. At this setting, the sled should color the snow with the unburnt fuel in the exhaust. From there, start to lean it little by little until the combustion cleans up...you may still be painting the snow with fuel at this point. Then, I personally like to go a little further until the sled stops painting the snow with exhaust. At that point, I stop. You can tune fuel up or down a little depending on power, which you will feel the sled getting stronger as combustion optimizes. However, stay on the rich side to keep the pistons cool while climbing. Finally, the larger the piston bore size or increasing boost, the richer you should run it.

I run a 600 cc turbo at 12.8 to 13.0 on the gauge, not because the number, but because that is what the sled wants. It has been happy for may years at 12 psi. Comparatively, most 4 stroke engines achieve MBT (maximum best torque) at 12.8. My 400 hp capable viper is setup to run 10.8 to 11.0 at 30+ psi to cool the pistons. From 12 to 16 psi, that same sled runs 12.3 to 12.5 all day because that is where it is happy without going to lean. It makes more power at 12.8, but the lower number keeps the engine cooler without sacrificing much power.

In short, tune the sled to what it wants, not a number. It will tell you what it needs, from there stay on the side of extra fuel without sacrificing throttle response or crispness. Also, the sled will be lean on light throttle, 15 to 17 is not uncommon. But, keep in mind, lean is not bad in that situation because there is relatively no load on the motor to create heat. Lean is not what melts pistons, it is heat generated under load without sufficient fuel to cool the pistons.
 
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Octanee

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Like previously mentioned, AFR is just a number that depends on a lot of factors. Tuning a 2 stroke is not the same as a 4 stroke. 2 stokes are more sensitive to heat and thermal management. Therefore, a best practice is to enrich the fueling until the sled starts to misfire and sputter at WOT. At this setting, the sled should color the snow with the unburnt fuel in the exhaust. From there, start to lean it little by little until the combustion cleans up...you may still be painting the snow with fuel at this point. Then, I personally like to go a little further until the sled stops painting the snow with exhaust. At that point, I stop. You can tune fuel up or down a little depending on power, which you will feel the sled getting stronger as combustion optimizes. However, stay on the rich side to keep the pistons cool while climbing. Finally, the larger the piston bore size or increasing boost, the richer you should run it.

I run a 600 cc turbo at 12.8 to 13.0 on the gauge, not because the number, but because that is what the sled wants. It has been happy for may years at 12 psi. Comparatively, most 4 stroke engines achieve MBT (maximum best torque) at 12.8. My 400 hp capable viper is setup to run 10.8 to 11.0 at 30+ psi to cool the pistons. From 12 to 16 psi, that same sled runs 12.3 to 12.5 all day because that is where it is happy without going to lean. It makes more power at 12.8, but the lower number keeps the engine cooler without sacrificing much power.

In short, tune the sled to what it wants, not a number. It will tell you what it needs, from there stay on the side of extra fuel without sacrificing throttle response or crispness. Also, the sled will be lean on light throttle, 15 to 17 is not uncommon. But, keep in mind, lean is not bad in that situation because there is relatively no load on the motor to create heat. Lean is not what melts pistons, it is heat generated under load without sufficient fuel to cool the pistons.

Thanks for the reply, I understand what your getting at, I know the 2 stroke is much more sensitive to heat than a 4 stroke, on my ol apex I ran it at 11-11.5 all day. I've unfortunately melted down a 2 stroke engine before due to it running too lean, so seeing the lean numbers down the trail is a bit scary to me and what had me worried so I wanted more input on that. I get what you mean with the a/f down the trail, it's safer to do so due to no load as you mentioned I want to add more fuel to be safe, safe is cheaper than an engine, it will also help reduce the chance of detonation.

Good point on over fueling it until it sputters then cut back, I had it at about 10. 5, it didn't like that, I've pulled it. Back to 11.5 and it's ran alright at that. Unfortunately it's been a dry winter with little snow so far so I haven't been able to do the tuning I'd like. I know I'll need to check the plugs, but I'll play on the side that's safer than leaning back. Also in a longer pull the engine heats up more and more even with the same a/f so to start a bit lower would be safer as well in a long pull.

Good info guys I appreciate it all and I'm sure for anybody wondering the same stuff this is all valuable! :thumb:
 
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