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Jerky engine turn-over


Orgoth225
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Hello I ought a old yamaha xs400 a few days ago and when I bought it the bike rode fine. The problem now is that I think I flooded the engine by not turning off the pet cock properly. I checked the oil and when I drained it was brown muddy and smelled of gas. Before I completly drained the oil I tried to kickstart it and the bikes starter seemed more stiff then usual. Even with my full weight (250 lbs) it would go half way down then on the second it would go down but with a-lot of back pressure. I know I will probably have to change/clean the plugs and get new oil but I.m worried of internal piston damage. The engine turns over just with more force then it should.

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The carbs should not have overflowed into the engine in the first place. They have overflow lines out the bottom, make sure they are not blocked, or looped up to keep them from overflowing.

Pull the plugs and kick the engine over. You're really risking bending a rod trying to start it how it is if the cylinders are full of gas.

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Just the hoses or blocked them somehow? There should be a nipple on the bottom of the carb that will leak gas if you leave the petcock on and fuel leaks past the float needle. Make sure those are operational before you do anything else. Hydrolocking a motor is assured carnage. I've seen hackjobs where people block those off instead of fixing the problem with carb, and end up destroying the engine.

A wheeze from the cylinder is normal. If you don't have compression, you'll feel it in the kickstarter.

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I would pull off the float bowls and look at the brass overflow tubes that run up from the base of the bowl. Make sure they're clear, and make sure they aren't cracked on the sides. When the fuel level reaches the point of overflowing, fuel must be able to pass over the top of the tube and drain out the bottom. Otherwise, it has nowhere to go but down the intake tracts and into the engine.

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I would try taking the plugs out and letting the compression chambers air out - if there's fuel, you could really screw something up, or at the least, it just won start.

In some electrical systems, the battery acts as a voltage regulator as well - if it is dead, even with a jump (or kick start) the engine won't run.

Does it sputter like it's sparking and trying or just nothing?

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even if you have a kickstart is it possible for it to fail with a dead battery?

Yes, You have to have some juice to get spark. Points ignitions can fire on very very low charge, but it won't run for long since most stators need power going in to energize them before they can put power out.

Do you have spark? You might be smelling gas if you're trying a ton to start it with no spark, since the fuel is just gonna hang out in the cylinder and not get burned.

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