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Old 12-04-2012, 04:15 AM   #16
No Marks....
buls4evr's Avatar
Joined: Sep 2009
Location: Michissippi & Nuevo Mexico
Oddometer: 2,318
It sounds to me as if you might be missing the most obvious thing here...

The carbs have not changed. It probably ran well once, so if they are clean and flowing the pilot circuit then...

Is the engine sealing properly? Bet that mag side crank seal if pulling air like mad. That will also cause a hot condition and make really erratic running. Got to pull that flywheel and replace that 60 yr old seal I think. Maybe the primary drive side too.That seal is probably not rubber anymore.
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Old 01-21-2013, 06:21 PM   #17
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Joined: Nov 2007
Location: Phoenix
Oddometer: 217
Agree with response #16. As for mixing ratio, assuming the jetting is the same, it was set for a 20:1 ratio. You aren't hurting the engine by running the same ratio unlike some are implying if the bike was originally jetted for 20:1. Just because modern synthetics can be run leaner, it's also assumed its in conjunction with modern liquid cooled engines. Air cooled motors have greater piston to cylinder wall clearance. More oil helps fill the gap. Dyno tests on a DT 250 using castor oil demonstrated more oil increased horsepower (reduced friction). The test demonstrated peak HP was found at 15:1. The trade off was decreased plug life due to fouling. Wear increased with less oil coincident with decreased horsepower. If I recall 32:1 caused measurable scuffing. Your 1966 motor more closely resembles a DT 250 than it does a modern liquid cooled motor. De-gummed castor based oils are still considered to be excellent 2-stroke lubricants when used at temperatures above 32F. (At lower temps the oil tends to separate from the fuel). I still give that study credence when applied to vintage motors. It would be interesting to see a modern unbiased study with synthetic oils on both air-cooled and liquid-cooled motors. If anyone knows of a link please post it.

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