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If thats a piston port then reed valves would be the best idea to getting EFI working reliably, with some other issues to overcome. Then you need expansion chambers on the exhaust Without reeds on the inlet carbs would be way easier to setup for it. Main reason is blowback, the mixture can travel through the carbs twice or more depending on RPM. With reeds blowback is eliminated. If it was mine I'd ditch the auto lube as well and go premix, get a set of 30mm flatslide mikunis, make chambers and fit reeds. Injected 2 strokes are rare, I think its only Bombardier/Rotax doing them with their E-Tech setup. Its direct injection as well. As 2 strokes are total loss lubrication the oil in the exhaust will upset the 4 cycle exhaust sensors, Also air cooled two strokes don't like running lean at all, they overheat & sieze, wrecking the barrels. I think you will kill it with EFI, sensors & computers unless you keep a very close eye on exhaust temps. Main reason is its not just air & fuel, Its oil as well and without knowing the oiling ratio how will it know how much fuel to squirt? Premix would help here. 2 strokes can be fine tuned with oil ratio. But the method tuners use is plug colour & exhaust temp. They also tune up differently depending on oil type, mineral, synth or castor. If you could get an oil tolerant sensor, ran the same oil at the same ratio and got a specific two stroke map it might work, but I would try it on something less rare than that first. Set it up using Gordon Jenning's guide, use exhaust temp & plug chops to set the mixture. Select carb sizes based on the tables in his bible. Also 2 stroke carbs are setup differently to 4 stroke carbs https://www.amrca.com/tech/tuners.pdf Many years have passed since Gordon Jennings first published this manual. ... Let's journey back to 1973 and read the book that was the two stroke bible of that ... wildemere fucked around with this message at 11:31 on Apr 4, 2015 |
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Apr 4, 2015 11:04
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I'm a bit of an old school two stroke user, I made a bit of an effort post here earlier. I'm glad you got it running on EFI. But I'm still worried about that little vintage two stroke running modern four stroke induction. Without reed valves, fueling and oiling will be a big issue. I see it has crankcase oil injection (controlled by a cable from the gas pedal) as standard and that was designed for 16-20 or so HP on a piston port motor. If you are hoping to increase the output then better lubrication will be critical. I would either delete the Subarumatic oiling system completely and go 30:1 premix on synth or 25:1 on castor. Or overhaul it completely paying special attention to the little end/cylinder bore crankcase bypass and supplement with at 10:1 or so in the gas tank. Make sure the oil pump is still operational from the gas pedal. A long run downhill with the throttle shut can kill an air cooled two stoke. I'd hate to see that little guy lean out and sieze. Locking up the wheels at highway speed... Ask any two stroke guy how he knows... With oil use fully synthetic Silkolene or Motul bike oil, or even better, castor oil for that sweet smell. (only two stroke guys know this) Actually running castor can give as much as 10% more power under high load conditions and its varnish combustion byproduct is also a lubricant. This also gives a few seconds of control under the previously mentioned full throttle seizures, Mineral oil is instant death, Synth less so, Castor is a 3 or 4 second rundown. The downside is ring sticking and more frequent rebuilds. I do it for the aroma and the safety. Read that Gordon Jennings book, its right in this era. Raise the exhaust ports and keep an eye on exhaust temps. Smooth out the transfers as well. Get a pyro kit like the Kart guys use, go for 1100 degrees Celsius about one inch from the head. These old two strokes are more like musical instruments than any other motors, they run on special resonance and tuning like artists and are as temperamental as such. But when performing well they are the dirty, screaming, smelly works of art I admire... The two stroke 500cc bikes from the eighties & early ninties pulled well over 200mph on carbies... around 180+hp Mercury 2 liter V6 outboards made over 300+ hp. on carbs, with methanol though.  This stock oiling setup would not do much more than 30hp tops, when adjusted correctly... Especially when your running lean. Or if that crankcase to top end lube passage is slightly blocked. Both the fuel & oil systems were gravity fed and the oil pump is attached to the throttle somehow. I'm not trying to rain on your parade just prevent a possible failure. The oil system is always total loss with two strokes and usually the failure mode when you get it wrong. Most power with old style two strokes comes from fuel type, expansion chamber design, exhaust port heights compression ratio, squish band setup. Then its the art of tuning... Ignition timing is fairly static until you get above 5 or 6 thousand revs. Then read the book. Its the opposite of four strokes... Then came variable height exhaust ports & digital ignitions... Hence the crazy power from 500cc GP bikes & Motocross bikes from that era. Still used carbies then as well. In my opinion a pair of 30mm flat slide carbs & 30:1 synthetic premix & a good two-stroke tuner would make more power than any "adapted from 4 stroke tech EFI setup" on that old piston port motor. Two strokes have a "big gulp" in-out type of induction without reed valves. Its very different from the constant vacuum of your average four stroke. wildemere fucked around with this message at 06:55 on Jun 4, 2015 |
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Jun 4, 2015 03:18
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