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yamsuzpolaris, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 156
Experience:  service technician on yamaha suzuki polaris products since early 70's. currently own and manage deal
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1979 yamaha XS1100 doesnt start and acts like it is not getting

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1979 yamaha XS1100 doesn't start and acts like it is not getting fuel. petcocks rebuilt, diaphragm rebuilt, carbs rebuilt. how do I know the vacuum advance is working? the vacuum advance and diaphram will hold vacuum with a tester. when trying to start I never see the vacumm advance move. just the spinning of the timing plate.


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hello. the vacuum advance has nothing to do with starting or not. the vacuum advance system will only really move when the engine is revving, it stays stationary when engine is starting and idling. first question is does it have spark, and then when cranking and checking spark plugs sparking be careful and manually move the timing plate to the advance position. see if it still sparks. a long time ago I seen this model where the wires broke completely inside the plastic insulation where wires curve to give slack to allow movement of the pulse coil plate. I found this by pulling on the wires really hard at the loop and the insulation just stretched cause wires were frayed and broke inside. if this isnt the issue you can squirt a little gas down each spark plug hole and reinstall the plugs and then quickly crank it to see if it fires off. when we test these bikes in the shop we use another gas tank held up high, hooked to carbs with a long fuel line and cap off the vacuum line to petcock. you can also cap off the vacuum advance hose, doing this allows you to access carbs, plugs, wires, coils, etc with the tank out of the way. rule of thumb: if you have gas, spark, compression, and exhaust the engine should run. and all this is taking into account who did the carbs was careful and did a good job and made sure choke circuits were clean. plugged choke passages and it wont start no matter what you do. if it fires and goes VROOM only with small amount of gas poured down the plug holes, then that means you have plugged choke passages.
yamsuzpolaris, Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 156
Experience: service technician on yamaha suzuki polaris products since early 70's. currently own and manage deal
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