Athena fuel mix
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@SpookDog (100/6000) x 100 = roughly 1.7% (1.666666667); not enough if Athena recommend premixing at 3%.
If everyone premixing at 3% is experiencing spooge dribbling over their swingarm/wheel/rear brake, to my mind what that shows is how clean and convenient Autolube really is for road-going two-strokes as it varies the delivery rate from something like 120:1 at tickover and low load applications to around 20:1 when you're flat out with the throttle pinned. And it works very well on road bikes which have a much more complex set of requirements than competition bikes. Consider a 17-year-old full licence holder, in 1994, buying an RGV250 as their first big bike; they're getting performance and technology that would be enough to win an IOM TT a generation earlier, but because they've stretched themselves to buy it, they'll probably need to use it for everyday transport, commuting etc. meaning it will actually be ridden like it's in a race possibly 5% of the time. The rest of the time it will be sat in traffic or at highway speeds at part throttle and this is where an engine like that doesn't need anything like 3% oil premix, it's just oiling everything up. And this is where Autolube excels as it's literally mechanical engine management which alters the oil delivery rate according to the way the bike is being ridden at the time.
If then people running premix start discussing whether to drop their premixing ratio to 2% to avoid oily mess and Athena specifies 3% (they also state the 170 kit is for "race use only"), what that equates to is a very serious compromise being made, namely your engine probably won't be getting enough oil under high load conditions.
Premixing is great for competition bikes as in most cases they're designed to perform one isolated style of riding very well. So a modern trials bike can get away with 100:1 as 99% of the time it's being run at low rpm, most of the riding is extremely technical and precise so low engine speed is where you need the crisp responsiveness. Conversely a YZ125 being ridden properly spends most of its time at 11,000rpm so a 35:1 ratio suits it just fine as it's very difficult to oil up under those conditions (watch the 1994 MXDN where Paul Malin beat Jeff Emig and crossed the line 4th overall when they ran the 125s and 500s together in one race; he doesn't shut off anywhere). It's top entertainment anyway:
https://www.youtube.com/watch?v=RZFvdzH9M2Y&t=129s
One more example; when I was a teenager, something which is not part of the Human Race decided it would be rather amusing to disconnect the oil delivery pipe from the reed block on my 1990 DTR when it was parked outside a pub on a Friday night. Obviously I didn't know this and rode home whereupon it seized. But here's the thing; I rode through town at 30mph/low rpm for about 3 miles and the bike ran perfectly as far as I could tell (the oil pipe stub must have a check valve as it didn't show any signs of running lean), it wasn't until I got out onto the open road and twisted the throttle it actually seized. So even the residual oil from the the bike being ridden before its subhuman interaction was enough for a short distance all the time the engine was under low load conditions.
I really don't know why Athena recommend ditching the Autolube, they say this even when you fit their 125cc kit. Bikes with plated bores and Autolube include the KMX125 (and these are much faster than the DTR when properly derestricted), RGV250, KR1-S etc. I think if I fitted a 170 kit to a DTR I'd be looking at comparing the oil pump delivery rate of the DT125R, DT200R 3ET, DT230 Lanza etc. and making a decision about how to shim the oil pump based on that and my riding style, what type of riding I'm planning on using the bike for etc. You can measure the delivery rate quite accurately by running premix temporarily, then putting the female part of a syringe on the end of the oil delivery pipe and watching/timing it fill up at a given engine speed.
I've no real experience of living with an Athena-kitted DTR of any kind so this is just my opinion, but the chap who bought my '93 3NC with reconditioned Autolube pump, Athena 125cc kit, Zeeltronic etc. reports excellent performance and reliability in over a year of ownership.
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Athena actually recommend premix? Wonder why?
I started on premix when I was still sorting out the previous owners jetting. Accidentally ran the oil pump dry (was on a closed loop) and haven’t gotten around to rebuilding one of my spares (I honestly think they turn up in the night and ‘huddle’ I’ve never bought one but have three or four!)Commiserations on your experience with the species. I had one pull off my petrol pipe and light it up. I’d just spent 3-4 months doing it up for the mot (on a £17.50 a week giro) rode it half a mile into town to get a celebratory kebab. I heard the tank blow, it’d swollen up like a dustbin size before it popped!
The local asshole had even stuck around to watch
…Was a gs125. Back then I bought another one for £25 and had it built and back on the road in a few months
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I switched to premix as I was having problems with my autolube. I also run, probably, the wrong grade of oil. Premix works well for me on the DTR have been that way for around 10+ years now.
I also had to remove the thermostat as it was just running WAY TOO hot. Vapor unit claiming 110 degrees in the summer. Whipped out the thermostat and now sits at 60-70 under load.
My DTR has been so reliable that it's been a joy to own. Every other bike gives me anxiety about taking it out, but not the DTR. I have no hesitations taking that bike out. Brilliant bike.
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@HOTSHOT-III said in Athena fuel mix:
@SpookDog (100/6000) x 100 = roughly 1.7% (1.666666667); not enough if Athena recommend premixing at 3%.
Would that mean that Athena recommend 150ml 2T per 5litres of petrol?!…
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@SpookDog Yes mate, spot on
Sorry to hear what happened to your GS125. We used them as workshop bikes when I did the motorcycle mechanic's course at Merton College in south London (supplied by Heron Suzuki) and they were nice bikes to work on. I used to ride up there two days a week on my '88 3DB and it handled the 60-miles-each-way commute extremely well. Once I was on my way home and got knocked off by the proverbial right turning black cab so I had to wheel it back to the college and get the train home via the tube to Waterloo. Eventually got home about 10pm but with the state of the railways now, that would probably be quite an achievement these days!
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Any idea what ratio 200’s run? I can’t imagine the Athena needing more than 50:1! Especially with the synthetic oil we have now. That’s like belt and braces plus steel toecaps!…
60 miles is enough to want to make sure you have decent seat foam! I was getting fidgety halfway through a 70mile round trip!
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@SpookDog The DT200R also runs Autolube. Because of the way this thread has gone I've asked on the Aussie and North American DT200R FB groups if someone can check the oil delivery rate in their service manual so it can be compared to the DT125R.
https://www.facebook.com/groups/2895277973902854
https://www.facebook.com/groups/1580516368941309
It's a very interesting question though. At the MX track near Puddletown, they sometimes have an Enduro practice and I know of several people who've had problems with MX bikes oiling up when they try and use them for this; threading through the trees and riding over logs etc. you'll be spending a lot more time at part throttle than going full bore round a track so it can be necessary to reduce your oil ratio in this situation if you're premixing.
Some of the newer KTMs and Husky Enduro bikes have oil pumps but these are electric and linked to the fuel injection systems so the delivery rate will be mapped just like the EFi. The equivalent MX bikes don't have this in most cases, and not everyone likes it as it's just another onboard computer to go wrong. Although I have to say I loved it when I had my 250EXC as I could just treat it like a DTR, i.e top up the 2T oil, go to the garage and throw some fuel in, rock up at the track and do a few sessions and ride home. Had planned to repeat the experiment with one of the DTRs to see what it would do but I never got around to it unfortunately, gutted because my 3MB was faster than the other two and had road legal MX tyres and those suspension mods.
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@SpookDog OK I've just been directed to a free DT200R 2YY (Australia) service manual download. The Autolube pump specs are:
Minimum Stroke: 0.20-0.25 mm (0.008-0.010 in)
Maximum Stroke: 1 .85 - 2.05 mm (0.073 - 0.080 in)
Minimum Output: 0.50 - 0.63 cm3 per 200 strokes
Maximum Output: 4.65-5.15 cm3 per 200 strokesCompared to a '91 3MB DT125R the specs are almost identical:
Minimum Stroke: 0.15-0.2 mm (0.008-0.010 in (they give the same imperial figure for this!))
Maximum Stroke: 1 .85 - 2.05 mm (0.073 - 0.080 in)
Minimum Output: 0.30 - 0.50 cm3 per 200 strokes
Maximum Output: 4.65-5.15 cm3 per 200 strokesSo just the minimum output is different really. To this end I'd be inclined to set the Autolube near the upper end of the min/max output scale for the 170 kit as a starting point.
There is however another side to this; the 2YY DT200R runs the same TM28SS carb as the '89 onwards DT125R but as standard comes with a 150 main jet, a good deal leaner than the stock 210 or 240 found on the 125 (and a #25 pilot which is richer). So it may be that the 2YY is meant to be ridden at lower rpm, i.e it's assumed that because the likely owner will have more of an interest in "proper" off road riding rather than being a yoof, they probably won't cane it quite as much. In the 80s and 90s it was common knowledge that a properly derestricted KMX125 was faster than the KMX200, although the 200 was the better off road tool due to having a wider spread of power.
So I guess make of that what you will, it's a common feature of big bore kits that they don't really boost top-end power as much as midrange so you might find you don't really need to rev it as much.
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Absolutely! The low to mid range is really quite something. I’m cruising at 55 @ 5K rpm so nicely, I’ve just got a new 18T front sprocket to try. I’m hoping it’ll make me rev it more. I’m riding it like a 4/ single at the moment!
I’ve upped the oil to just about 2.5%. I’ve been limp mode riding before now. I’ve just gotten over a spell of the pilot jet and main jet being partially blocked! (I thought the new CDI was failing!) it seems the paper-like filter was shedding micro fibres!
New tap, new pipe, new filter!…Now that I can say it’s running properly! I’m going to get the auto lube refreshed and put back on…
Thanks for the info! Priceless!!
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