MTD 18.5 lawn Tractor Vapor lock


Old 03-28-12, 12:35 PM
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MTD 18.5 lawn Tractor Vapor lock

My 1996 MTD Lawn Tractor with a 42A707 B/S engine appears to start and run okay. Until running approx. 20 min. Then dies , and will not restart til later after some hours. Then starts up and runs good again.
Any possibility of Vapor lock? Parts breakdown shows the last 12" of fuel line to carb shows the line insulated. which I installed, after rebuilding carb. It also has the heat shield installed between carb and exhaust.
any suggestions other than cutting open some of the side panels? Or is it possible other gremlins are causing this.
BFHFixit we must be neighbors, with very similar backgrounds.
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Old 03-28-12, 06:27 PM
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Hello Dickij13,

From your description it sounds like you could have a ignition coil heating up and dropping spark, This can be easily detected by running the engine until it quits. Then remove both spark plug wires, Apply the parking brake and put a screwdriver into one of the wire boots. Hold the shank of the screwdriver with-in .030" of one of the top cover screws or any good ground then crank the engine over, If the coil is good it should jump a blue color spark to ground.

If you get no spark disconnect the small black wire that exits from the front cover just above the intake manifold with the spark plug wires, Test for spark again, If still no spark the coil is the faulty part.

Good Luck
Old 03-28-12, 08:32 PM
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I agree, most likely a bad coil. Especially on this model engine.
Old 03-30-12, 08:21 PM
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Thanks guys:
Iwill try your suggestions when it stops raining here. as working outside dosen't
go well with engine cowl open.

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