Jetting chart

[tfaith08]

I see a lot of questions rotating around jetting and power production and the manipulation of the latter by altering the former. Don't do it. Jet for accuracy, not power.

This is how your jetting works. Well, it's more of a means of getting the point across rather than showing extreme accuracy, but the idea is there. You want to get your jetting as close as possible to the best ratio of heat and combustion possible, which can be determined by stoichiometry. More fuel doesn't mean more power, unless you're too lean. Less fuel doesn't mean more power unless you're rich. If you have an engine that is set up properly, leave it alone.

The general rule of thumb is 12.5:1 amongst most circles. However, I have yet to find an air/fuel ratio that all builders agree upon, though most are between 11:1 and 13.5:1. The reason for this is that there are many more things in play than just air and fuel. A plug chop and knowing what to look for are going to get you where you need to be. For further information, refer to the plug chop and jetting guides in this section.

Trust me on this; I have a chart.

 

[rich1]

So you are saying to use an air fuel ratio instead ? How do you measure it ?

 

[jus_me]

by the plug....

 

[rich1]

I see a lot of questions rotating around jetting and power production and the manipulation of the latter by altering the former. Don't do it. Jet for accuracy, not power.

View attachment 9485


The general rule of thumb is 12.5:1 amongst most circles. However, I have yet to find an air/fuel ratio that all builders agree upon, though most are between 11:1 and 13.5:1.
Trust me on this; I have a chart.

How is the plug going to show 12.5:1 fuel ratio ?

 

[tfaith08]

A plug chop and knowing what to look for are going to get you where you need to be.

The plug will tell you how everything is going in your cylinder, just as a stoichiometric calculation will. The methods are quite different, but the end state is the same.

Are you asking how to do a plug chop or read plugs?

 

[motoman159]

How is the plug going to show 12.5:1 fuel ratio ?

Dude, trust him, he's got a chart

 

[rich1]

It doesn't. The plug will tell you how everything is going in your cylinder, just as a stoichiometric calculation will. The methods are quite different, but the end state is the same.

Not exactly ! I ve got a 04 Mach 1 Mustang that I ran at the strip for 2 years . I run a Compucar Nitrous kit on it and spray 100 hp to 125 hp. When you first set it up, you check plug readings to get you in the ballpark .Then you change the fuel and nitrous jets to get it right ! The plug readings from 100 hp to 125 hp look almost exactly the same . I can not rely on the plug readings to save a 32 valve v8 motor that costs 7 grand to replace. The only option is to use an A/F meter,I use an Innovate Wideband that costs $500.00 . The fuel ratio normally is set at 13.5 and with nitrous it goes to 12.0 I run 12.5 @115 in the 1/4.

 

[jus_me]

So put an air fuel meter on the blaster than.. Were talking about a Blaster here. Best thing you can do to read how your engine is doing is read the plug.

 

[tfaith08]

In your instance, you are using an additional fuel, which is going to cause your mixture to burn differently because the amount of hydrocarbons per volume has decreased. The fuel can (on average) attach to 13 oxygen molecules, leaving one more to be open because oxygen exists as O2. To more accurately describe the instance, a 25:2 ratio would be best because you can't exactly split the fuel compounds and retain the same properties.

When you introduce nitrous oxide (N2O), you are adding more oxygen to the cylinder and a corresponding increase in fuel has to be given. At the end, the remaining byproducts will cause discoloration of the plug in a different way than without the nitrous.

In addition, once you increase the pressure under combustion to that extent, you have to increase fuel flow to further reduce the inlet air temperature so as to fight knock, but the plug reads well with a 10:1 AFR because you're packing a great deal more heat into the cylinder and the plug can clean itself of the excess fuel as if it was at 12.5:1. This is why forced induction cars run lower than 10:1 and make optimum power.

 

[tfaith08]

The end result is the same. You want to make as much power as possible without excessive heat. However you do that is up to you or whoever else is tuning it. Whether you shoot for a plug color or run individual header O2 sensors, it doesn't matter.

It doesn't matter how you inflate the tires so long as you can ride the bicycle.

 

[rich1]

So put an air fuel meter on the blaster than.. Were talking about a Blaster here. Best thing you can do to read how your engine is doing is read the plug.

So put an air fuel meter on the blaster than.. Were talking about a Blaster here. Best thing you can do to read how your engine is doing is read the plug.

Point is an A/F meter wont work on a Blaster, so how can you use a chart ? I roadraced 2 strokes for 8 years . Those engines had Mukuni carbs with adjustable low and high jets able to set on the fly. The only way you could do it was by cylinder head temp and /or exhaust temp . The plug reading on a Blaster is one way but not the only way.

 

[jus_me]

It doesn't matter how you inflate the tires so long as you're kid can ride the airbus..

 

[rich1]

Are you asking how to do a plug chop or read plugs?[/QUOTE]

No, Ive been doing it longer than most... I want to see " The Chart "

 

[jus_me]

This seams like it is becoming more of a debate over who did what when and why.. I think what the guy was trying to say was. If you happen to jet a bit lean and you seam to have more power you better check your plug because you might just blow it up.. Better safe than sorry.. I am sure the drag bike guys ride a very fine line of to lean and just right.

 

[rich1]

This seams like it is becoming more of a debate over who did what when and why.. I think what the guy was trying to say was. If you happen to jet a bit lean and you seam to have more power you better check your plug because you might just blow it up.. Better safe than sorry.. I am sure the drag bike guys ride a very fine line of to lean and just right.

He said he had a chart.... that's not a debate ! What you just said above made more sense than what he said.

 

[tfaith08]

Point is an A/F meter wont work on a Blaster, so how can you use a chart ? I roadraced 2 strokes for 8 years . Those engines had Mukuni carbs with adjustable low and high jets able to set on the fly. The only way you could do it was by cylinder hear temp and /or exhaust temp . The plug reading on a Blaster is one way but not the only way.

Agree 100%. But...

An O2 sensor will work, but no one has come to an agreement on what the optimum AFR is.

A EGT probe will work, but you have a varrying loss of intake gasses into the exhaust port all over the RPM range, which is going to lower your readings quite a bit.

A head temp reading will work, but heat dissipation is going to vary with different head styles, compression ratio, overall power, and other things.

You can use several readings to get it spot on, but who's to say what spot on should be for all of those? For the Yamaha Blaster, a plug chop is the way to go to measure AFRs.

 

[rich1]

Dude, trust him, he's got a chart

OK !

 

[tfaith08]

Wait, can you guys see the chart I drew? That's the chart I was referring to. That last sentence in the original post "I have a chart" was a joking comment.

 

[jus_me]

I see a chart..

 

[rich1]

Agree 100%. But...

An O2 sensor will work, but no one has come to an agreement on what the optimum AFR is.

A EGT probe will work, but you have a varrying loss of intake gasses into the exhaust port all over the RPM range, which is going to lower your readings quite a bit.

A head temp reading will work, but heat dissipation is going to vary with different head styles, compression ratio, overall power, and other things.

You can use several readings to get it spot on, but who's to say what spot on should be for all of those? For the Yamaha Blaster, a plug chop is the way to go to measure AFRs.

An 02 sensor will not work on a 2 stroke..........An EGT probe works .....A head temp reading works.... these are established FACTS in the real world. Ive used them all in my job, racing and my hobbies !
The only thing I agree with you is.... a plug chop on a Blaster ...the rest is like you said ...a JOKE.