Operate with Clean Out Plugs NOT in

[BBastecki]

Out of curiousity, what damage can be done to the motor(s)/boat if you operate a Yamaha jet boat with the clean-out plugs left out?

 

[Scottintexas]

Probably none

After a while they may overheat since not much force will be going thru the nozzle to the intake screen

You'll notice no thrust immediately and not go long enough to overheat them though

 

[Wisefam22]

Thw force if more then idle will probably pop the hatch and kill the engines.

 

[MidnightRider]

I believe there has also been cases where the jet pressure has blown the clean out "tubes" loose and the jets then can flood the rear of the boat via the bilge filling up with water. That case was blown plugs though so maybe without the loose plugs in the way the pressure wouldn't build in the tubes and only blow the hatch.

 

[BlkGS]

When I first got my boat I made it about 150 feet before I realized I had taken them out after our last outing. I think it would be really hard to not notice something was wrong and cause damage. You literally will not go faster than normal idle speed without them in.

 

[Cobra Jet Steering LLC]

It should be obvious as soon as you try to accelerate it just will not go.
Usually you know something is wrong.
The real danger with those is if one comes partially loose when you are driving the boat on plane and it fills up the engine compartment with water that eventually gets ingested in the engines.
The second worst type of incident is if one violently blows out and blasts the hatch open damaging the latches and shutting you down instantly , if the plug launches in the air and lands in the water it stays lost forever .

 

[Jgorm]

Nothing happened when i forgot to put them in (except i couldn't go 5mph!)