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Post by 190mech on Nov 24, 2020 18:58:46 GMT -5
I dont think EGT is a good indicator unless we are talking super kart or 2stroke gp racing,,Ideal race iggy curve is high initial,then tapering as revs increase,so the pipe gets hotter and works as a shorter pipe..Problem with race curve is on the street a part throttle will give high advance and cause meltdown of the piston,,we sure dont want that,so your 14 degree flat liner is a safe street number and watch the CHT,then tune from there..2strokes are soo simple!!
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Post by 13brx3 on Nov 24, 2020 19:00:41 GMT -5
I have the capability to adjust the timing at any point, I'm just keeping a flat curve for simplicity, at the moment.the problem I'm having, is even with the main jet as large as I can go, and it still come on the pipe, the cht and egt are higher than what I'm reading they should be.
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Post by 190mech on Nov 25, 2020 5:09:22 GMT -5
Jet needle too fat?What kind of cooling fan does it have??
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Post by 13brx3 on Nov 25, 2020 8:18:32 GMT -5
It's the shallower of the two needles that are available for the cp carb. I'm running the oe Yamaha fan.
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Post by ThaiGyro on Nov 25, 2020 17:49:32 GMT -5
Hey 13brx3...just read the thread and responses. All good stuff, as these guys know their shite. Not sure how new you are to this forum or what you have read. My tuning is somewhat old school. Maybe because 2T's are?
On my engines, via my own and others bad and good experiences, I have come to always tune ignition timing first, then fuel/air tune to it, (and the pipe) and lastly CVT tune to get the most poop to the ground.
Ignition timing is as hard to get right as anything I have done...but it it the most often overlooked. SO, I think you asked the right question. When racing TZ's, I never had a problem with tuning on the West coast of the US, but always had problems at Daytona. I simply had too much advance. Atmospheric pressure and humidity screwed my brain sideways. Even morning (practice and qualifying) were so much better than the afternoon races.
Not sure if your desire for the right combo is near those limits, but I suspect you are on the right track. If you have good records and know the best setup to date...sneak up on timing with the OEM setup. A tenth of a degree advanced...when the power is on the pipe, is a lot.
If you can map your ignition curve, or at least read it...you can get a visual of what it's doing. Not sure what is available today. I am fairly sure that no ignition manufacturer will provide their units specs.
A good data acquisition system will record it...likely along with a dyno setup. It can be quite different under load than static.
An EGT probe? Nice. Consider the method of ignition bumping with no other changes...until you are scared. Then back it off by half of your setup and try air/fuel tuning.
BTW...I am not a fan of tuning an air box with no snorkel..it is the device that adds air volume/pressure to your box. The tuning parameters for 2t fun and pleasure are snorkel length and girth. (and more)
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Post by 13brx3 on Nov 25, 2020 19:22:05 GMT -5
Hey 13brx3...just read the thread and responses. All good stuff, as these guys know their shite. Not sure how new you are to this forum or what you have read. My tuning is somewhat old school. Maybe because 2T's are? On my engines, via my own and others bad and good experiences, I have come to always tune ignition timing first, then fuel/air tune to it, (and the pipe) and lastly CVT tune to get the most poop to the ground. Ignition timing is as hard to get right as anything I have done...but it it the most often overlooked. SO, I think you asked the right question. When racing TZ's, I never had a problem with tuning on the West coast of the US, but always had problems at Daytona. I simply had too much advance. Atmospheric pressure and humidity screwed my brain sideways. Even morning (practice and qualifying) were so much better than the afternoon races. Not sure if your desire for the right combo is near those limits, but I suspect you are on the right track. If you have good records and know the best setup to date...sneak up on timing with the OEM setup. A tenth of a degree advanced...when the power is on the pipe, is a lot. If you can map your ignition curve, or at least read it...you can get a visual of what it's doing. Not sure what is available today. I am fairly sure that no ignition manufacturer will provide their units specs. A good data acquisition system will record it...likely along with a dyno setup. It can be quite different under load than static. An EGT probe? Nice. Consider the method of ignition bumping with no other changes...until you are scared. Then back it off by half of your setup and try air/fuel tuning. BTW...I am not a fan of tuning an air box with no snorkel..it is the device that adds air volume/pressure to your box. The tuning parameters for 2t fun and pleasure are snorkel length and girth. (and more) Very great post, thank you so much. The ignition I am ruining is fully programmable but universal, I'm running the same ignition on my rd, except for it's a 2 channel unit. I'm starting with a flat curve for now, but once things start to act properly, I'll start to add an off pipe timing curve, maybe even pull timing on the top end to bring the pipe back into resonance. That being said, I feel like the timing is already excessive for the fuel I'm running. I want to get a good baseline with the stock timing, and have enough time to make changes all on the same day. I plan on trying to get the CHTs in check with timing, then start to pull fuel until I get to the upper "safe limits" on both cht and egt. I'm not looking for the absolute maximum power, but I would like the most power than I can get, without compromising reliability. As for the snorkel, I could not find any data on how to calculate the snorkel length or diameter. I'm familiar enough with the Helmholtz Resonance, but not enough to pull a formula from thin air 😁. Thanks again for the post, when I finally get to do all the testing, I'll post my results so everyone can laugh with me or at me. Allen
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Post by ThaiGyro on Nov 29, 2020 16:17:45 GMT -5
I would say you may not need much help...sounds like you have a good plan. I can only offer that, in general, we have set initial advance setting in the +20.5 to 21.5...or higher, depending on pipe and carb tuning. Must get it fired off!
How you back off/retard your advance is the hard part. Mild tuned, non adjustable ignitions tend to only back off to ~16 to 18 degrees in a gradual recession from 2 to 3k rpms until a low-ish redline.
We have seen moto-crossers that initially peak above 24 degrees, yet back down quickly as they reach pipe happiness fast due to short range gearing. They might be at 8 or 10 degrees at 10,000 to 12,000.
I think you can safely set something like initial 20.5 degree tapering down to 12-ish after maybe 3 or 4000 rpm. Just a guess, but having the ability to adjust it is part of the fun...and adventure!
If you can measure AFR at specific rpm's...maybe you can set your map pushing those targets.
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Post by 13brx3 on Nov 29, 2020 20:46:03 GMT -5
Great info! Regardless of how it seems, I need all the help I can get. On my rd, I have the base timing set to 17*, then it peaks at 3500rpm/27*, then tapers back to 17* by 9000rpm. I figured my scooter being much higher cylinder pressure and a much smaller bore wouldn't require nearly that much timing. I holed many a piston on my old kawasaki triples, and I think it was largely due to excessive timing. I may be thinking about it wrong, but hopefully pulling timing will bring down the CHTs, and allow an added safety margin so I can try to pull fuel until the EGTs peak. It's nice having all the data, to see what effects timing and jetting make. If it doesn't help at all, at least I know what not to do.
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