Third time no luck

[miller347]

Ok so changed rotary valve, cleaned carb of Port side engine. Sounded promising and take it Lake and then the other engine stumbles and cuts off and if i baby it will run to 3k and dies... At the same time the engine I worked on wouldn't Rev over 2500..... Tomorrow I check the natural safety switch but prolly will not fix the stumbling

 

[Dr Honda]

You could have a bad switch... but that wouldn't "Kill" the engines.


I'd say to double check the rotary valve. Sounds like you are out a few degrees.

 

[Sportster-2001-951C-Stock]

Low pressure leak check the fuel lines, and make sure he fuel shoutoff valve isn't plugged or leaking.

A leak somewhere in the fuel lines will cause the fuel pump to suck air, and fuel starvation, so will a plugged fuel valve.

The fuel/water separator cup o-ring is a common leak point also the fuel shutoff valve has o-rings in it that dry out and fall apart. A new replacement valve and/or bypass it for confirmation testing.

How was it running before the carb rebuild, backtrack and think about what was done since it was running correctly, assuming it was.

 

[miller347]

You could have a bad switch... but that wouldn't "Kill" the engines.


I'd say to double check the rotary valve. Sounds like you are out a few degrees.

I did not replace the rotary valve on engine that's stumbling, but still worth a check tho

Low pressure leak check the fuel lines, and make sure he fuel shoutoff valve isn't plugged or leaking.

A leak somewhere in the fuel lines will cause the fuel pump to suck air, and fuel starvation, so will a plugged fuel valve.

The fuel/water separator cup o-ring is a common leak point also the fuel shutoff valve has o-rings in it that dry out and fall apart. A new replacement valve and/or bypass it for confirmation testing.

How was it running before the carb rebuild, backtrack and think about what was done since it was running correctly, assuming it was.

I will double check fuel system today. But it's odd that both engines will not pass 3k.... But I'm not sure How the boat runs.... I've never had it on the water since I got it last year [emoji35]

 

[Sportster-2001-951C-Stock]

Some boat models are RPM limited while in neutral, the neutral switch will interlock with the cranking starter as well. Mine won't start unless the shifter is in neutral but it's not rev limited in neutral.

Not sure which boats were RPM limited, maybe all the 787 versions. The 951 versions aren't AFAIK.

So maybe that's what's happening.

The other thing that can cause limited RPM is the voltage regulator rectifier. You can make a quick test by disconnecting the rectifier/regulator and see if the motors will rev. Could be system voltage rises too high, this interferes with the ignition system.

You really won't be able to see how well the motors perform under load until you splash it, running on the trailer is only one part of the test and they can often run great on the trailer and not very well in water. If it's not running well on trailer then don't expect an improvement in water.

If your fuel pumps are divorced from the carbs (not integral) those original pumps were a bit weak and have begun failing. The integrated pumps are not as troublesome. The replacement divorced fuel pumps are upgraded.

Unless there's something quite afoul in the fuel system, they typically run great on the trailer. The reason is there's no load on the engines thus just a small amount of fuel is enough but when those throttles go to the wall in water the fuel system has to be fueling or else the motors will fall on their face and lean stumble.

So yeah, now it sounds like either a voltage regulator issue or neutral switch is limiting RPM.

There are other things that can happen, such as an exhaust leak will fill the bilge with inert gas and displace oxygen thus the fuel won't burn.

Exhaust system rubber hoses can delaminate internally, blocking the exhaust and causing excess exhaust pressure.

Check the low hanging fruit first, it's just a matter of going through the possibilities till you find it.

 

[miller347]

I changed one rectifier so one is new, when I bought the boat guy tome me he was running it last season till the rectifier went bad...... I have replaced the rectifier, rotary valve, cleaned both carbs, new battery, my nxt thing to do is check the natural safety switch today. But other than that I'm out of ideas

 

[Sportster-2001-951C-Stock]

I'm leaning towards the neutral switch as well, consider you'd have two bad rectifiers if it was doing it on both motors with the other motor not running. The rectifier can't cause overvoltage when the stator isn't spinning so one motor off with bad rectifier the other good one revs just fine till both are running.

The neutral switch keeps you from cranking in forward and I believe reverse, so that should be an easy test. No crank "in gear" should be the result. And, no rev limited in neutral position.