Rpm's dropping

[Cobia270]

I'm having a problem maintaining rpms between 2000 and 3000 as soon as I can get it above 3200 it seems to be holding. Have had other issues with rpms but nothing like this. Any help would be appreciated.

[Cobia270]

Forgot to mention 2001 200 hpdis

[Cobia270]

Rodbolt any ideas?

[rodbolt17]

don't run it at that RPM.

[Cobia270]

What kind of answer is that? Obviously something is wrong that it won't hold at those numbers. Thought I'd get some help here .Thanks anyway

[Cobia270]

So just ignore the problem? Would you go 80 miles offshore knowing the problem can get worse? Thought it might be an injector problem which I've never had.

[Cobia270]

I just changed both fuel lines from tank to water seperators. Really didn't want to open vst if I didn't have to. Only put about 10 hours on it so far this summer due to surgery. Everything new in spring.

[Cobia270]

Primer bulb doesn't collapse. I've had issues with the high pressure pump,bad plugs and clogged filters before and with those problems I was never able to maintain rpms at a certain point like now. That is why I thought it could be something else.

[rodbolt17]

at that RPM some hulls simply are plowing and lugging the engines.
it could be either engine has an issue and is pulling the other down.
could be clogged filters in the VST,injectors, or engine.
each of those engines has about 12 filters under the hood.
could be an o2 sensor.
could be a lift pump leaking.
could be a bunch of things.
only way to tell is by monitoring fuel pressues and spark Kv at the failure RPM and load.

[Cobia270]

Would putting it on a computer show the problem or would it be a waste of time and money?

[rodbolt17]

if its a sensor feedback issue it may show up on the laptop.
if not it wont.
remember the computer is rather stupid.
its up to the tech to actually interpet what the screen displays.

[Cobia270]

So I went down to boat today to see if i could fix the problem. First I pulled the plugs and although they weren't fouled there was some carbon buildup on them after only about 15hours. Any way cleaned them up and reinstalled. Next I opened up the vst tank to find the filter with some brown residue on it. Cleaned it up reinstalled everything and took the boat for a ride. Boat ran great in fact it seems the other engine wasn't keeping up. I'll have to do the same to it. The carbon is a bit of concern after such little use so I will monitor. Thanks for all the replies.

[dngharvey]

It may not be fuel related at all, I have a 90 and a 115, both two strokes and they both gradually lose rpm especially when running in chop. A previous 70 did the same, I'm wondering if there is a friction device that can be adjusted to help with this?
Haven't had a chance to study on it yet as it is fine above 3200 or so.