2001 115 4stroke loses rpm

[hwoodyone]

I run twin 115 4strokes. My port engine four trips ago started dropping rpms at wot. Drops to 3700 and then varies slightly. There is no skipping, sputtering, missing etc. I can stop and fish for a short while and the engine runs wot for a while and starts process again. All fuel filters, hoses, squeeze bulb replaced and tank checked. New water pumps. Engin still the same.
Last trip I made a visual inspection and discovered the top right valve cover bolt had fallen out and was hidden under the block. I replaced the bolt, checked the other bolts and launched. The engin ran perfect for the two day trip.
Next trip this weekend, the engine ran great wot for 15 minutes then started same old thing again. RPM dropped down to 4400.
What is going on? Thanks

 

[loyoki]

Re: 2001 115 4stroke loses rpm

1) when RPM drops down, stop engine and unscrew spark plugs one by one; check them, are they all black and dry ?
2) check oil if normal, no water ?

If this is OK, I will give you some more advise

 

[hwoodyone]

Re: 2001 115 4stroke loses rpm

Thanks, I'll check next trip. Unfortunately my boat is 380 miles away in Fla. I'm in Wilkes Co. Ga. What does the dry black plug mean?

 

[BOAT DOCTOR]

Re: 2001 115 4stroke loses rpm

check the vst has a filter on bottom of high pressure pump seen dozens.

 

[loyoki]

Re: 2001 115 4stroke loses rpm

Thanks, I'll check next trip. Unfortunately my boat is 380 miles away in Fla. I'm in Wilkes Co. Ga. What does the dry black plug mean?

= good

 

[loyoki]

Re: 2001 115 4stroke loses rpm

check the vst has a filter on bottom of high pressure pump seen dozens.

Yes but after because if there is a problem in oil or/and spark plugs (this is the easiest job to make yourself), then it is not the VST, perhaps he lost a cylinder.

 

[rodbolt]

Re: 2001 115 4stroke loses rpm

my money will be on a clogged VST filter as well.
mechanical damage wont come and go but trash in a filter can.
like Boatdoctor I see at least 5 per week on various 2 and 4 stroke outboards and sterndrives.

 

[hwoodyone]

Re: 2001 115 4stroke loses rpm

thanks to you all. I'll change filter first and go from there.