70 hp mercury low power

My 70 hp merc has no power an

My 70 hp merc has no power and seems to splutter etc it has great compression on all 3 cylinders and good fuel supply and spark the guys at the outboard shop reckon its either a reed valve or the casing is worn between the cylinders so the cylinder that is firring etc is not sealing is there anyway i can confirm this or do i need to pull it down to find out

"Alan,

If a reed valve is b

"Alan,

If a reed valve is broken you should be able to make a positive diagnosis without taking the engine apart.

If you remove the carbs and place a vacuum gauge over the intake flanges, one at a time, you will notice that the vacuum is absent or low in one or more intakes as you crank the engine.

If you do not have a vacuum gauge, you can simply place you hand over the flange and crank the engine. If there is a broken reed, you will feel pressure instead of vacuum as you crank the engine.

As for the casing being worn enough to cause the problem that you mention, I would say that the compression would be very low if that were the case.

I don't know what year engine we are talking about, but I would check the pressure in the fuel line between the pump and the carbs. I would also verify that the ignition is actually working properly. Some ignition systems can seem to have spark, but the spark may not really be good.

Give us the year and serial number and we can be more specific about advice.

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