Athena 170 dyno session
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Today me and the DT had a date with the dyno
First I convinced myself to put in a exhaust temp probe, I don't have much experience from that and thought I could learn something. I tried it on the moped once, and it was mounted too close to the port, and temp went low on full throttle. So, this time I mounted it maybe 15cm from the cylinder piston face, and it worked very good.
I started with running with the power valve in 10% steps to see the effect, and used that to make a map for it. It closes a lot more than the stock setup, and does almost nothing in 0-30% area, but I left it like that with full stroke anyway, and start opening it at quite low revs, since it seems to do some good around 3k. It also seems to make the bike slightly quieter when 'creeping'. Open power valve makes a lot more exhaust noise than a closed one, that's for sure!
After I had the PW map, I made a static ignition curve at 10deg, and then added 5 degrees per run, so 10, 15 and 20 to find where the engine responded to more ignition advance. Based on this I made the ignition map. It did a lot on the over-rev to increase the advance again after the engine was 'off the pipe'. I found the same on 23cc rc-engines I tuned before. After this I could increase the rev limit from 11 to 11,5k. Before it was 'dead' at 11k, but now it's usable to 11,5k. I could also see that the stock curve ignition retard made the exhaust temp rocket at over-rev, but with the added advance on top it stayed more constant. I had a short reading of almost 900deg once with the 'stock curve' in the Zeeltronic around 11k, that scared me a bit.. I think advance was around 5deg at 11k then. Max exhaust temp is 700-750deg now. If I try to lower it I lose power, and there is not much power anyway (it's not a high strung 2-stroke). The 1,5mm sensor seems to react very fast, faster than the meter that updates around 1Hz. Short blips on the throttle, and the temp jumps up instantly.
Finally I tried some main jets, but I could not improve on the stock main jet. I left in a slightly richer jet that gave almost the same curve as the stock setting, just to have some margin. Stock was Mikuni 125, and the slightly richer was a 'no-name' 140 (probably from china). 'No-name' 130 seemed to be same or slightly leaner than Mikuni 125.
The stock carb is 26mm, and maybe it could make some more power with a bigger carb. I have a 28mm that fits on the reed-side, but it needs another 'snorkel' to the airbox, because the connection is bigger on the carb. Maybe I could find something from some old motocross bike that I could modify. I think the original 'snorkel' is a bit small in diameter too, so putting something bigger could also help.
Not sure if it is worth the effort though?I made s quick test drive after the dyno, and it feels just like the curves indicate, more usable rev range, pulls better from the bottom all the way to the top. I thought I heard some knocking around 8k when driving, so I backed the ignition a little bit in that range, but I need to do some more testing.
I posted the pictures in another forum for those interested: https://www.warp7.se/forum/viewtopic.php?p=36158
Please note that the rpm/torque on the graph for the 125cc cylinder is wrong (rear wheel power is correct though), because I changed the gearing after I installed the bigger cylinder.
The setup is the following:
-88 DTR
Athena 170-kit (cylinder raised 1,5mm and reworked/bigger combustion chamber, squish area 50%, 0,8mm squish)
Athena pipe
Zeeltronic CDI
Stock 26mm carb and airbox -
@Rallyfinnen Cool write-up, very interesting.
If you're doing dyno work with temperature probes, ignition advance experiments etc., you've explored this further than I have. But based on the fact Yamaha completely redesigned the DTR after only one year in production including changing bore and stroke and adding the TM28SS flat slide carb, if you have one it would absolutely be worth trying it. Not only that but early versions of the DT200R (3ET) also run the TM28SS so I would suggest it is appropriate for a DT125R even with a 170 kit fitted.
Perhaps getting a carb-to-airbox rubber would be as simple as ordering the later version which fits the TM28SS carb? It would be good to take a look at this anyway as when the DTR was new, Yamaha didn't make a very good job of sealing where it joins the airbox; this is of course downstream of the filter element which means your engine could suck dirt when riding off-road. I sealed mine with a product called Seal-All which is a petrol- and oil-resistant glue:
Unfortunately to make a really good job of this it is necessary to remove the airbox completely so the part you've glued can sit horizontally until cured but it's well worth doing for peace of mind.
Aside from the Zeeltronic ignition, what is your full setup, pipe/silencer, airbox, reeds etc.?
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That's quite low power readings to be fair. I think you have a lot more potential out of that motor.
Definitely need a bigger/better carb on that.
I run the VHSA 32mm carburettor found on the TZR 125 RR Belgardas which ran an altered 3MB engine, which is about as close to the DTR engine you can get really.
It's a really good fit and I find my 170 absolutely flies along! I am going to have a dyno session soon and I'll post up the pics as well as Carb tuning, and Zeel timings.
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@HOTSHOT-III Sounds good if the new version would fit the other carb I have! What's the diameter of the TM28SS connection on the intake/airbox side? Maybe somebody has a spare carb and could measure? I used 'car windshield glue' for doing similar glue joints before, that held up well too.
Basic spec is in the end of my first post. Reeds are carbon I made myself from 0.3mm sheets (Polini I think). I bought some online, but I thought they were too thick and stiff. I always want as thin as possible (without getting flutter) for throttle response. Reed cage is standard, I thought it looked like it would flow good enough. I'm not sure changing the reeds made any difference either.@Calum For sure, max power is not a lot, but pretty happy with the wide band on the engine. Getting a higher revving pipe, widening the exhaust, raising the cylinder more etc would probably get the power up, but would probably sacrifice some of that power band too. I need to drive it for a while to make up my mind on that.. The dyno gives realistic to low readings, and this is rear wheel power, so crank power will be a couple of horses more.
Please be aware that the Zeeltronic tunings depends on the 'calibration' of the power valve and ignition. I tuned the end points of the power valve to maximum stroke, so that can vary from servo to servo, and bike to bike. Zeel recommends some other end point values, but I prefer doing things my own way
When checking the ignition advance with a (known good) timing light, I found I had to change the 'trigger angle' from 80 to 67deg to get the actual ignition advance to correlate with the set value in the Zeel. Seems this can vary from bike to bike too. According to Zeeltronic, this should be 80deg on the DT, but not on my bike, this means set map values would be way off from reality. I made a static advance map (constant 10deg) and made markings on the flywheel to check the actual advance with a timing light.
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I did a bit of googling, and it seems the TM28 has a 50mm diameter connection to the air filter, can somebody confirm this?
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It sounds right. I’ll measure one when I get to my shed in a few hours…
Definitely could do with the 28 fitting, no reason not to…
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I think there could be some benefit of a bigger carb too. The 28mm Keihin I have is 50mm too, so if the TM28 is the same, I should be able to use the newer 'snorkel' to the airbox.
I wrote down my settings as they are at the moment, so I thought I would post them here too
Ignition:
1000 17
2600 25
5000 18
8500 16
9000 12,6
10000 14
11000 24PV:
2300 0
3900 30
5900 50
7000 75
8000 100Will not apply to any engine for reasons I mentioned before.
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Thank you! Then the newer snorkel will not fit the Keihin..
