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Post by Deleted on Jul 2, 2017 7:36:07 GMT
Extra oil in the air fuel mix leans the ratio off. You are wrong this time Dont be fooled into thinking it is only air being pulled in that will lean the mixture. Too much Oil does the same. But, as He's unlikely to ride it like Bill Ivy across the top of the mountain it will likely be OK. I can't see how oil being pulled into the crank through the seals could lean the mixture. Could you explain the process? Too much oil in the petrol, yes I can see that would lean the mixture, but in the case we're talking about the correct mixture will be pulled through the carb, to which is then added a small amount of gearbox oil. Nope, I can't see how that could lean the mixture. And bear in mind that as described, it's not pulling in much oil, the smoke is coming from oil that's seeped through the seal during hours and days of being stopped. A two stroke relies on crank case compression to transfer the fuel/air mixture into the cylinder for combustion to then take place. If an oil seal is letting by it leans off the mixture. How much by depends on the state of the seal. In this case not very much! They are simple things with only 3 moving parts. We got away with running on a retired sidecar competitors donated 25:1 when we became separated from our service crew with our correct 40:1. But squeaky bum time but it was the choice of retiring on the spot or keeping your fingers crossed.
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Post by Telemachus on Jul 2, 2017 7:41:57 GMT
I can't see how oil being pulled into the crank through the seals could lean the mixture. Could you explain the process? Too much oil in the petrol, yes I can see that would lean the mixture, but in the case we're talking about the correct mixture will be pulled through the carb, to which is then added a small amount of gearbox oil. Nope, I can't see how that could lean the mixture. And bear in mind that as described, it's not pulling in much oil, the smoke is coming from oil that's seeped through the seal during hours and days of being stopped. A two stroke relies on crank case compression to transfer the fuel/air mixture into the cylinder for combustion to then take place. If an oil seal is letting by it leans off the mixture. How much by depends on the state of the seal. In this case not very much! They are simple things with only 3 moving parts. We got away with running on a retired sidecar competitors donated 25:1 when we became separated from our service crew with our correct 40:1. But squeaky bum time but it was the choice of retiring on the spot or keeping your fingers crossed. If an oil seal on the generator side is "letting by" it leans the mixture by sucking in air - agreed. If the clutch side seal is leaking it doesn't pull in air, it pulls in oil. A much smaller quantity due to the viscosity of oil vs air. Thus a clutch side leak doesn't lean the mixture, well not until the oil level is depleted such that air starts to be sucked in.
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Post by Clinton Cool on Jul 2, 2017 10:30:45 GMT
I've tried a couple of motor bike forums but had very little response, much better here. There seems to be no limit to the knowledge of Thunderboat members The other problem I have is that the float valve and needle are slightly worn. I've given both a thorough clean but when I watch the action of the needle it has some sideways movement, as well as up and down. From time to time either the needle sticks down, petrol pours from the carb overflow, or up, the engine starves of fuel and dies. The only repair kit I could find in the U.K. was for the 76 model (mine's 82). Bought it but the thread diameter of the seat is different. I'm now faced with the problem of sourcing a part with no legible size markings on it. Bit of a nightmare! Look at DT 125 MX bits, they were in production until '82 I'm half certain they used the same motor. Good shout that one. There are plenty of rebuild kits for the MX, less than a tenner. Applying my brand of logic to this, the only crucial thing is that the diameter of the thread that goes into the carb body should match the existing one. Then, if the hole inside the valve is different it doesn't really matter, as all it's doing is starting and stopping petrol coming into the carb, rather than doing any tuning. Obviously the fitted valve should protrude the same or very similar amount to the existing one as well. Does my logic hold good? Also thinking through the possible damaged crank seal: If it has gone, and the engine relies on compression from the crank area, should I expect to feel air being sucked, if I remove the gearbox dipstick and put my hand over the hole?
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Post by Deleted on Jul 2, 2017 14:29:28 GMT
Look at DT 125 MX bits, they were in production until '82 I'm half certain they used the same motor. Good shout that one. There are plenty of rebuild kits for the MX, less than a tenner. Applying my brand of logic to this, the only crucial thing is that the diameter of the thread that goes into the carb body should match the existing one. Then, if the hole inside the valve is different it doesn't really matter, as all it's doing is starting and stopping petrol coming into the carb, rather than doing any tuning. Obviously the fitted valve should protrude the same or very similar amount to the existing one as well. Does my logic hold good? Also thinking through the possible damaged crank seal: If it has gone, and the engine relies on compression from the crank area, should I expect to feel air being sucked, if I remove the gearbox dipstick and put my hand over the hole? Unlikely. You can pressure test two stroke engines but it's a lot of arse aching about. Here's the basics of how your motor works 👍🏍 www.animatedengines.com/twostroke.html
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Post by Deleted on Jul 2, 2017 14:50:54 GMT
To be honest, this is a question probably best asked on a forum for motorcycle mechanics rather than a forum of sweary, chip shouldered bigoted weirdos. Oi! I'm not chip shouldered !!
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