Athena 125 with Athena pipe on dyno
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@Rallyfinnen All pretty interesting stuff, thanks for posting. I bought an Athena 125cc cylinder kit to do a DTR engine build last year, the bike is now sold but I still have a full set of Athena 125cc A, B and C piston kits (there's like 0.01mm difference in size between them). Replacing the piston often on cylinders with plated bores helps preserve the roundness of the bore for longer (hence why I bought them), if you'd like to buy them from me let me know and I'll do you an eBay listing.
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@HOTSHOT-III Thank you for the offer on the pistons, but I don't think I'll be needing them.
@Calum
I have a 170-kit on the way too, I think the bike needs a bit more power (mostly low/mid band) to make it more enjoyable to ride.I used photobucket extensively years ago, until they ransomed the pictures. I refuse to make the same mistake again.. Maybe limited image size would be an alternative? 1MB images or even smaller should be pretty sufficient. People tend to upload the mega-resolution pics that phones do today, but if resolution is scaled down they are still good enough for forum pics.
How are the engine vibrations with the 170-kit, compared to standard? Have you adjusted the balance factor (crank & balance shaft) to the new piston weight? I don't like engine vibrations, makes it tiring to ride the bike, so I worry about that with the 170-kit. The plan is not to open the engine atm, just install the kit.
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Those 19 hp - are they on the back wheel or crankshaft?
Original spec is 23 hp (crank), so if 19 hp is wheel then that would suggest 21% loss in transmission which sounds a bit high for a motorbike.
Of course a 35 year old bike is expected to lose some, I'm just wondering.
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The 170 kit on my setup is bloody awesome! I love it so much I bought 2.
Is it as fast as my RS or Cagiva... No. But I learnt long ago that the DT just isn't that type of bike. I have had my Athena ported and the bikes tuned and it rides just lovely. Pulls really well and is so much fun to ride!
With regards to vibrations, yeah that could do with dialing out. After long rides it feels like I have haptic feedback on my phone switched on. But I ride invariably so it's something I can live with.
I will get my bike dyno'd this year and post up the results...
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Piston and crankshaft counterweight should match each other. Increase the mass on one keeping the other the same causes more vibrations.
In fact, there are two optimums regarding the counterweight - one gives the least vibrations but a bit more bearing load, the other the least bearing load but a bit more vibrations.
Extra balance shafts are typically removing secondary vibrations from the conrod, so if the mass of those is the same they should still be right.
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Interesting, I would love to be able to dial away some of the vibration. It’s such a high frequency it sets my bones on edge sometimes…
I had a really strange thing happen a couple weeks ago. I was waiting on a roundabout to pull away and a car came by towing a huge caravan. It had the absolute worst squealing brakes that I’ve ever heard! The strange thing is my bike seemed to ‘pick up’ the frequency! The rest of the ride home my engine & expansion chamber was ‘ringing’ with weird harmonics! I Shit you not! 🫤
It sounded kinda like an overhead camshaft that was lacking oil! WTF?!… -
I have the Dellorto VHSA 32mm Carburettor as found on the Rotax series of engines. I originally source a 4DL carburettor and saw another VHSA on eBay. I made a very good one from both of them, thinking at the time they were the same. They were not and therefore jetting on my DTR is WAAAAYYY different to that of the 4DL VHSA.
All I will say is, jet to suit, what works for my setup (bearing in mind how unique my setup is) may not be good for you.
But in essence, it's like a 140 main jet with a U13 needle (IIRC) But I bought the whole range. I don't run oil pump and have advanced the ignition + ported barrel with VForce4 Reeds and airbox delete with an underslung pipe. All of those will have factors on jetting so kinda take my setup with a pinch of salt.
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