Jetting chart

[rich1]

View attachment 9485

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.

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.[/QUOTE]

 

[tfaith08]

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 !

They will work on 4 strokes, no doubt. But before you can measure air fuel ratios on a 2 stroke by measuring the head temperature, you better have a pretty good grasp on several variables, all of which will vary from application to application, therefore making it an unsuitable solution for the rest of us if one person figures it out for his/her application. If cooling capacity is increased, head temp will change, but nothing has been done to affect the AFR or AFR requirements.

As for an EGT reading, again, variables. Acceptable AFRs are going to read very similarly across several applications whereas EGT readings will vary drastically. An engine with only a pipe is going to generate less heat than a full build generating 3x the power. With performance 4 strokes, you are absolutely correct. EGTs will be very close throughout several variables.

Arlan Lehman uses plug chops to get accurate fuel requirements, that's all I'm saying.

the rest is like you said ...a JOKE.

Say what now?

 

[rich1]

Arlan Lehman uses plug chops to get accurate fuel requirements, that's all I'm saying.
Who is that ? Does he have a chart too ?

 

[tfaith08]

I'm all for an in-depth discussion, but for you to tell me what I'm saying is a joke? Got it.

I'll tell you why EGTs on a 2-stroke don't work as a perfect AFR gauge, which is what this thread was meant for. I have an 86 LT250R that I installed an EGT probe on. I built it during the winter and got the jetting really close to being too lean, but still fine and wrote the EGT reading down. That next summer, I took it out and rode it and had EGTs that were over 200f higher, so I upped the jet size. It dropped by about 60f lower than the winter reading. So I did a plug chop. The plug was on the dark side of good, but it was white specked so I got some C16 and mixed it 75/25 pump/C16 at 40:1. It dropped back down again. I put the previous jet in it (small) and it came back up higher than the winter reading, but the plug was fine now. After abut 10 min of riding, the EGTs were back up to about 150 over the winter reading, so I pulled the plug and it was colored fine, but white specked again.

After the increase in AAT, it started to knock, raising the EGT reading. After I reached operating temps, it started to knock again, raising the temps again. If I was using only the EGTs to measure AFRs, I'd have been 20 kinds of screwed up on jetting. In the end, a plug chop got it right. IIRC, the range for the ordeal was 255f and a 182 and 185 main for a 39PWK. 255f is quite a gap for a 1 size difference in jets. It tells of too many things to try and get you one answer.

If you go off of EGTs to set your jetting, good luck.

For every reason you have to use an EGT, I have 50 other forum members who recommend a plug chop, which was the original method I recommended for gauging fuel requirements.

 

[tfaith08]

I'm sure someone will come along to tell you who Arlan is before too long

 

[Blaaster]

Arlan Lehman is a person who uses plug chops to get accurate fuel requirements.

If iI got anything out of the former posts, it was that the best way to select the correct jets is to to rely on a plug chop.

 

[MrTwoJay]

You have to go old school with a 2poke, unfortunately. .. the oil will ruin the pricy o2 sensor and that is not something you want to replace often....

Monitoring plugs, temp is perfectly acceptable practice.

 

[Awk08]

i know who arlen is, he wears a lab coat

 

[DUALSTROKE]

Nobody is setting there jetting by egt on a single cylinder 2 stroke.. It is all done on a plug chop and temps. The guy that is derailing your thread tfaith only knows keihin carbs, not mikunis. If that makes any sense. Not knowing who Arlen is tells you what he knows. Hell he had to put a junk ass mikuni on cause he had to WAIT to jet his keihin on his blaster. Make sense? NO!!! I am always up for a good read but not some clown derailing the thread over a chart and his previous folded dealership days. Believe me he is not using an egt probe either. He is the joke....

 

[rich1]

Nobody is setting there jetting by egt on a single cylinder 2 stroke.. It is all done on a plug chop and temps. The guy that is derailing your thread tfaith only knows keihin carbs, not mikunis. If that makes any sense. Not knowing who Arlen is tells you what he knows. Hell he had to put a junk ass mikuni on cause he had to WAIT to jet his keihin on his blaster. Make sense? NO!!! I am always up for a good read but not some clown derailing the thread over a chart and his previous folded dealership days. Believe me he is not using an egt probe either. He is the joke....

I still have more respect for the OP than you, at least he can site reasons/examples for his opinions and knows the difference between winter and summer tunning.You rather take stabs at me or my families previous 1.5 million a year Honda dealership.FYI..Bussiness did not fold , both father and son of my wife died, then her mother had a stroke that paralyzed her, sold it to take care of her. I care about knowing who Arien is about as much as you and youre so called backyard racing exploits.Like the OP said this was a discussion about A/F and EGT measuring devices that real racing teams use. Plug chops are the easiest way to check but not the only one. You are right though, no EGT probe just going to use a HTS and RPM ! Thanks for your concern .

 

[rich1]

I'm all for an in-depth discussion, but for you to tell me what I'm saying is a joke? Got it.

I'll tell you why EGTs on a 2-stroke don't work as a perfect AFR gauge, which is what this thread was meant for. I have an 86 LT250R that I installed an EGT probe on. I built it during the winter and got the jetting really close to being too lean, but still fine and wrote the EGT reading down. That next summer, I took it out and rode it and had EGTs that were over 200f higher, so I upped the jet size. It dropped by about 60f lower than the winter reading. So I did a plug chop. The plug was on the dark side of good, but it was white specked so I got some C16 and mixed it 75/25 pump/C16 at 40:1. It dropped back down again. I put the previous jet in it (small) and it came back up higher than the winter reading, but the plug was fine now. After abut 10 min of riding, the EGTs were back up to about 150 over the winter reading, so I pulled the plug and it was colored fine, but white specked again.

After the increase in AAT, it started to knock, raising the EGT reading. After I reached operating temps, it started to knock again, raising the temps again. If I was using only the EGTs to measure AFRs, I'd have been 20 kinds of screwed up on jetting. In the end, a plug chop got it right. IIRC, the range for the ordeal was 255f and a 182 and 185 main for a 39PWK. 255f is quite a gap for a 1 size difference in jets. It tells of too many things to try and get you one answer.

If you go off of EGTs to set your jetting, good luck.

For every reason you have to use an EGT, I have 50 other forum members who recommend a plug chop, which was the original method I recommended for gauging fuel requirements.

What ever works the best for you as you stated above .
The EGT/ CHT I used in roadracing since you had to race for 1 hour on a roadcourse. Im not calling what you said a joke it was the way you presented it and said you were joking ! Plug reading will only get you in the ballpark , but gray ,tan or black all have many shades of lighter and darker .Piston crown and combustion chamber reading will tell even more but take time and effort than a normal person will not undertake. Meters , analog and digital CAN tell you whats happening in real time. If they were not useful tools then most every R&D programs by manufactures would be useless.However I don't disagree with you that the plug reading are easy/ useful for the Blaster .I try to find a different way to do things... if they work or not..,you wont know till you try. But now with FI entering into the dirt bikes more those above measurements are the even more useful, in fact , vital. I deal with this all the time at my job with OBD 1,2, repairs on cars and am Certified for FI too. Thanks for youre insight !

 

[rich1]

I'm sure someone will come along to tell you who Arlan is before too long

Found him on the web....Is he the guy that builds those pipes that leak ?

 

[tfaith08]

Found him on the web....Is he the guy that builds those pipes that leak ?

Yeah, the guy that holds those 2 stroke building records. That's him.

 

[Larry's Shee]

Your chart is slightly flawed. Power doesn't drop off that fast when you go from ideal A/F to lean. That's the problem, you won't/can't notice the drop, and it will be running GREAT, for a little while.
Worse yet is the ex temps start to soar, which will melt a piston. And it might not even have signs of deto.
This is why it's best to jet on the rich side, plugs are cheaper than pistons.

 

[Wifesblaster]

LOL at this thread!

 

[tfaith08]

Your chart is slightly flawed. Power doesn't drop off that fast when you go from ideal A/F to lean. That's the problem, you won't/can't notice the drop, and it will be running GREAT, for a little while.
Worse yet is the ex temps start to soar, which will melt a piston. And it might not even have signs of deto.
This is why it's best to jet on the rich side, plugs are cheaper than pistons.

Agreed. It was meant for the guys that come around asking about jetting for more power (only jetting, at that). It isn't an accurate chart; I just tried to be somewhat informative in one aspect.

Wifesblaster, see what happens when I try to do something nice for the community? Lol, how are those shocks coming along?

 

[Wifesblaster]

The problem is you can't argue with a "Know it all" type of person.

I should be able to look at the shocks this weekend. I havent forgot about ya.

 

[tfaith08]

I wouldn't say that rich is a "know it all" kind of guy, just that his wrench time comes from 4 strokes, or so it seems. Might I be right, rich?

 

[rich1]

I wouldn't say that rich is a "know it all" kind of guy, just that his wrench time comes from 4 strokes, or so it seems. Might I be right, rich?

Stated my background before, Ive been on both sides of the 2 and 4 stroke fence.However, I could tell that you knew more than you joked about too. As far as me " knowing it all" .Its a web-site..." Why So Serious" ? No offence , just opinions that should be openly discussed not attacked.

 

[rich1]

The problem is you can't argue with a "Know it all" type of person.

I should be able to look at the shocks this weekend. I havent forgot about ya.

Ok here is youre chance, whats this 2 stroke tool used for ?