Jetting with EGT's

[RemeberMe]

I might have the chance to get my hands on some EGT equipment to help determine the correct jetting on my bike this spring. What I'd like to know is if this is a viable method for tuning the jetting for the different circuits of the carb.

Once on the bike you can run 1/4,1/2, WFO, whatever, and it will read and display (and even record!) EGT and RPMS. A lot of the snowmobile guys I know run them with a lot of luck, but I was wondering if this would be a desired method on a bike. Also, what temp range would I be gunning for? Is this method better than reading the spark plug? All comments are welcome, please let me know what you think.

Thanks,
Andrew

 

[A.J]

Hello Andrew, there are a lot of variables that come into play with the EGT as well. It is not the end all of jetting but just another tool to use from my experience. Probe placement and desired/target temps are the 2 biggest and in a nutshell you still have to do plug readings to match what the probe readings are trying to tell you. It is tough to pull a number out of the air and say that is the optimum temp I should be running at.
I have a set on an old sled and they work great on it ( sustained to the bar riding) for telling you how hot you are running but I feel if you have an accurate "butt dyno" that you are better off doing that on a mx bike.

 

[RemeberMe]

Thanks A.J,

I'm new to this jetting thing, so the more tools/monitoring equipment/feedback I can get, the better it'll make me feel about doing this :). I feel like I can probably tackle the main jet with confidence, but its tuning the part throttle circuits that tend to scare me a bit. That's why I ask, will the EGTs help me tune partial throttle openings, i.e. 1/4, 1/2, ect.?? Like I said, I have access, and it's free to use, so getting it to use isn't the problem, it's just determining if the information presented will be worth my time that it'll take to fit it to the bike. I noticed that you seem to shy away from the idea, but for a jetting newbie like myself I feel that it might be worthwhile providing the information it gives is usefull. Any thoughts considering the criteria? As if jetting doesn't already have enough variables, I'll have to admit that I'm just another one without the experience/confidence.:)

Thanks for your time,
-Andrew

 

[cujet]

I use EGT probes on a twin two stroke. My opinion is that they are only useful at full song. The reading varies largely at various partial throttle openings. I think the only way to use EGT as a partial throttle tuning tool would be to calibrate the throttle position in an accurate manner, such as in a lab. Otherwise the temp changes with slight load changes.

Chris

 

[RemeberMe]

Thank you Chris.

So in order to tune part throttle with EGTs the load has to be consistent otherwise the EGTs will fluctuate. How much fluctuation have you seen between various conditions?
I would think that rejetting would be required if the conditions were to severe because the bike would require more fuel under more load (like switching to sand after it was set-up for hardpack track/trail, even with all other conditions being equal) which would bring EGTs back down to a desireable temp. Am I wrong in assuming this? Seems like a truck towing a trailer (i.e. more load) is going to use more gas as opposed to one that's empty.

 

[A.J]

All good questions, Andrew, however developing your butt dyno is the way to go on a mx bike. Experience comes from doing and observing and no one was born knowing a whole lot, lololol.
Save the hassle of installing the EGT and go and buy a few jets both ways of what you are running now. Make sure you keep notes and change one jet at a time and see what difference it made.The needle and pilot to needle transition is the most important on a mx.It takes time and patience but it's worth it. After some changes and note taking you'll get a handle on it. Also there is a really great jetting thread either in the KDX Forum or at the very bottom of the Forums page and it makes some great reading to see how those guys dialed in the jetting on their bikes. Lot's of good info in that thread, it's pretty well an online jetting course..........check it out!

 

[RemeberMe]

Thank you A.J, I appreciate the feedback. I really need to get this down because of the different riding I do. Temp ranges between 30-100 degrees depending on the time of year, and I do trails, dunes, and would like to start beginer MX. I thought that EGTs would help simplify the procedure and remove some of the guess work. Oh well, I'm not new to learning the hard way if you know what I'm sayin':)

Thanks again,
Andrew

 

[RemeberMe]

A.J,

Any idea where that thread was? I find a lot of stuff when I do a search on 'jetting', even if it's forum specific.

Thanks in advance,
Andrew

 

[Rich Rohrich]

Here are a couple of threads that cover EGT and tuning :

http://dirtrider.net/forums3/showthread.php?s=&threadid=37556&highlight=EGT

http://dirtrider.net/forums3/showthread.php?s=&threadid=12179&highlight=EGT

 

[RemeberMe]

Um, WOW! Thanks for the insight Rich, I appreciate the links.

That's a lot of info to digest so I'm going to go sit in my corner now and maybe I'll understand most of it by Thursday. Thanks to all that commented, but I think I'll be steering clear of the EGT monitoring equipment.

Happy New Year!:)
Later,
Andrew

 

[A.J]

Andrew, I do not know how to post links so go to the technical forum (pretty sure it is the next to last forum) and punch in "show all posts from the beginning".
Check out the RB Designs Emergency jetting info post. It covers needle and pilot selection and slide cutaway/needle interaction.It is a great jetting thread.
Rich also has an excellent spark plug reading thread under the "need jetting help fast" heading in that same forum. Also a very good discussion about humidity and jetting in there.