Sports Jet 175 engine misfire / dying

[jonstret]

Hi

I have a Nautica jet rib from 2001 with a Sports Jet 175 engine from (carb version). We have had the boat for 2 years and it has been trouble free. This last two days I have had a problem with the engine misfiring / dying after running over 3300 RPM. It will trundle around all day at less than 3000 rpm. It will pickup and run on WOT for 20 or 30 seconds and then misfire for about 10 - 15 seconds and then die. It restarts immediately but will repeat the same every time is works above 3300rpm. The same happens if you slowly build up the revs.

The only thing that has changed in the last week has been I refuelled with regular unleaded rather than the super that I normally use. There is no obvious leak or lose connection and the fact that it picks and runs for 20 - 30 seconds before dying confuses me (although that isn't difficult )

We are away on a two week holiday and I am keen to get the most out of the boat (and amazingly for the UK we look like we will get good weather for the next couple of days )

Before I start fiddling does anyone have any experience of this problem?

Thanks

Jon

 

[jonstret]

Re: Sports Jet 175 engine misfire / dying

I have some more information that may help

The engine serial number is oe396672

I have checked and believe that is has a black stator as there are blue and black wires that come from the flywheel (although there is a bunch of cables from the flywheel with this pair being held together with a piece of yellow sheathing.)

When the boat is running all is well until after about 20 - 30 seconds of running at speed (20 + mph or over about 3300 rpm) Then the engine starts mis-firing. Whilst the boat does slow it continues to run for a further 10 - 15 seconds. The mis-fire then gets worst and even if you reduce throttle or increase it the engine will stall. It will then restart fine and continue fine so long as you don't open the throttle too much.

Any thoughts ?

 

[kend301]

Re: Sports Jet 175 engine misfire / dying

Sounds like a fuel problem , are the carb vents clear and are the floats properly adjusted ? Also these things were plagued with fuel pump problems .
Start by pulling the fuel feed off the lower carb and check flow if it pulses the pump diaphragm is bad , rebuild the pump .

 

[jonstret]

Re: Sports Jet 175 engine misfire / dying

Ken

Thank you. She wouldn't start at all this morning. I have removed the pipe out of the fuel pump and getting nothing at all. Looks like your diagnosis was right. Hopefully I can find someone locally to fix asap.

I will let you know when resolved so you can chalk up another successful diagnosis

Thanks

Jon