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Normal cold compression range on mc43 earthquake 2cycle cultivator
Few 2-stroke engines produced in these modern times aren't exhaust tuned which means it is difficult to test the compression pressure with any accuracy at cranking or starting speed - most are exhaust tuned so a much greater power output can be produced from a small and lightweight engine. Peak compression happens at the engine speed when the reflected exhaust pressure wave effectively blocks the exhaust port. At this point the engine capacity grows, the compression ratio increases and the power output increases.
I don't know what the compression pressure should be but I would be slightly worried if it was less than about 90 psi and expect to find a reading of 100/120 psi. As it is a twin, the real test will be the difference between the cylinder pressures which theoretically should be identical though for practical purposes a variation of about 10/20 psi would be acceptable.
The best test of engine condition is how it starts, runs and sounds. When considering a 2-stroke engine it is important not to forget there is also compression under the piston. Sometimes after wintering unused a previously good machine will be down on power and difficult to start. It should not be ignored how if the crankshaft oil seals have lost flexibility, air could be drawn past them into the crankcase reducing the quality of the induction through the carb.
11 hours ago
I am trying to adjust the idle and high rev on my dx d830 straight shift trimmer but don't seem to have any set screws like the ones on line can you help tell me anything about setting idle and high rev on this one and what the gas ratio in for this trimmer
Not sure about the fuel/oil ratio. Modern 2-stroke engines are designed to run with less oil due to concerns about pollution and 50:1 isn't unusual. That was the recommendation for my strimmer but I added a little extra oil to maybe 30 or 40:1 and it gave good service for 30 seasons.
The fashion for anti-pollution measures also spread to the fuelling of small engines especially in some areas. In this case the fuel/air adjustments are either hidden behind plastic or metal plugs or deleted from the carb altogether.
If there are no screws it is a preset type and if dismantling and a thorough clean doesn't restore performance it is reasonable to make one of two assumptions (or maybe both) - either the carb is faulty in some way (diaphragm perhaps) or the crankshaft seals are failing and allowing air into the crankcase preventing a good induction.
It isn't unknown for a small 2-strokes to perform well all season and then be next to useless after standing idle all winter. If this is the case it is worth suspecting those seals have lost flexibility...
on May 27, 2020
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