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Engine Knocking


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My monsoon 340 engine is knocking. It feels like I am kitting something. Most people I talk to seem to think it is bad gas. I have about 1/2 tank left. I am going to to add some octane booster and let the fuel get as low as possible, but any other suggestions.

I also replaced the spark plugs this winter, but it ran fine for a few months.

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Sounds like detonation, you may also want to check to make sure your distributor hold down bracket bolt is not loose, it may have slightly advanced on it's own. If so you could do more damage if your not 100% sure where you timing is, just something to double check.

Edited by 68Slalom
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Sounds like detonation, you may also want to check to make sure your distributor hold down bracket bolt is not loose, it may have slightly advanced on it's own. If so you could do more damage if your not 100% sure where you timing is, just something to double check.

Were the spark plugs exact replacements? I have seen a cross referance lead to the wrong plug and that cross ref plug was much longer than the original.

Fuel would have to be pretty bad to make it knock all of the time. If they are a cross reference plug, look them up in the book again. Pull them to make sure nothing hit them.

Timing is critical... I agree to check it first thing.

Did you check the gap on the new plugs?

If the engine is running hot could contribute to knocking. Is your water flow good? Impeller?

A blown head gasket can lead to knocking and loss in power...

Check for cracks in the cap or loose spark plug wires....

Any vaccum leaks. Could cause a lean condition under a load...

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Sounds like detonation, you may also want to check to make sure your distributor hold down bracket bolt is not loose, it may have slightly advanced on it's own. If so you could do more damage if your not 100% sure where you timing is, just something to double check.

Were the spark plugs exact replacements? I have seen a cross referance lead to the wrong plug and that cross ref plug was much longer than the original.

Fuel would have to be pretty bad to make it knock all of the time. If they are a cross reference plug, look them up in the book again. Pull them to make sure nothing hit them.

Timing is critical... I agree to check it first thing.

Did you check the gap on the new plugs?

If the engine is running hot could contribute to knocking. Is your water flow good? Impeller?

A blown head gasket can lead to knocking and loss in power...

Check for cracks in the cap or loose spark plug wires....

Any vaccum leaks. Could cause a lean condition under a load...

Using NGK. enigine is running at 160 deg same as it always has. I am going to dble check the gaps this w/e, knocking seems to happen at lower speeds.

Here is one thing, I replaced the prop, went from a 515 to a 525 and now my RPM's are higher. use to cruise at 30mph/32k RPM now it is about 34.5K RPM, no lose in power, in fact I picked up a couple MPH, 46 to 48.

Edited by DeltaDan
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Took it into the warranty mechanic, Indmar is replacing the transmission under warranty.

That's the next thing I was going to comment on, are you sure the noise is coming from the engine :)

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