Re: Weird JW compression test.

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July 14, 2018 at 1:21 am #79521
cajuncook1
Participant
    quote Stanley:

    I’m using a gauge with a short hose and threaded plug hole end.The numbers I get are consistently 80 lbs by hand and barely 70 with drill.I can use the drill,lay it down,rope it over 5 times and get it up to 80.For comparison I have a good runner of the same model that is steady at 85lbs spinning it with drill or pulling it over by hand.This motor absolutely will not Idle or start without a shot of gas into intake.I have taken carb and mag plate off the runner and put them on it with no change.It has to be an issue with the power head.The higher number says it should idle but the lower would explain why it doesn’t.I’m stumped.

    Stanley, even with a compression of 70/70 psi, the motor should be able to start and idle decently without having to shoot fuel mix into the intake. Remember introduction of fuel mix into the crankcase takes sufficent amount of pressure differences with in the crankcase.

    Things that can cause poor introduction of fuel into the crankcase.(excluding carburetor issues and compression)

    -broken or fixed reed valves/leaflets
    -obstructed or partial obstructed intake or exhaust ports.
    -obstructed or partial obstructed exhaust housing or lower unit foot.
    -worn or damaged piston skirting

    These conditions can prevent proper air flow through the crankcase and thus prevent proper fuel/air delivery.

    Easiest things to check and ruleout are lower unit foot and exhaust housing obstructions from trash, insect nest, build up of fuel/oil mix goo that clumped up over time obstructing air flow out.

    May not be your issue, but if you have ruled out your carburetor, ignition, and you have decent compression, then these are possible issues.

    Cheers,

    Cajun