F200XCA dropping from and not reaching max RPM

[Ducowti1]

2016 200FXCA with 500hrs, well-maintained. Intermittently she will struggle out of the hole at WOT, and max out about 5-600rpm less than 6100max. No rhyme or reason. Also happens while running, will suddenly drop rpm and infrequently will pop back up to max while running.
- Fuel is good, always from reputable E-free pump. Always E-free gas, never more than a month to burn a tank
- fuel filter element changed regularly, and this week most recently. No water in that filter housing.
- fuel/water separator changed regularly, and this week most recently. No water in fuel.
- VST filter at bottom of tank changed this week. Original/existing filter was nearly black, so figured that would be the cause - it wasn't
- AFTER the VST lower filter replacement didn't fix, yesterday replaced the VST F-filter at top of tank - will run it today but the existing filter wasn't discolored like the black filter in the bottom.

Anyone experienced same? My internet-fu has turned up most likely issue would be that VST-bottom fuel filter, and that wasn't it. Local shop replaced the fuel filter and F-filter in top of VST in January and that seemed to address for a few months until recurrence around March.

Thanks for your replies.

[99yam40]

change plugs, inspect the ones pulled
hard to find intermittent miss

[Keithbaja]

I would run a foot or two of clear vinyl hose at the motor. Watch for air (bubbles) or hose colapse

[TownsendsFJR1300]

I had a very similar issue with my F150 with low hours.

It was a bad spark plug cutting in and out. They all looked fine.

Replaced them all, that fixed the issue (did nothing else).

I'd replace them all...

.

[Ducowti1]

Thanks for the replies gents. Amazing to me that a reputable shop in a coastal town (i.e. is pretty much always busy) never thought to consider the plugs.

Incidentally, while replacing the VST filters, I discovered the rectangular (sorry don't know the part name) water cooling box on the face of the VST was probably close to 50% occluded w.salt sludge. The shop that replaced the F-filter in Jan saw the photo I took of the sludge and said 'that motor never gets flushed'. I flush it w.the hose bib, every time for 20min, never once failed to flush after running in the saltwater, bc I can never get adequate suction w.the rabbit ears (round or rectangular) through the lower unit, which I know is far preferable. Does the water really need to be warm-to-hot to dissolve the salt to prevent that sludge?

[Keithbaja]

Townsend, I'LL bet they weren'T NGK... Ducowti- you might want to look into flushing with "Salt Away" Damn good Snake Oil. Don't flush it out.. leave it in the motor..the part ur describing sounds like the fuel cooler..

[TownsendsFJR1300]

Townsend, I'LL bet they weren'T NGK... Ducowti- you might want to look into flushing with "Salt Away" Damn good Snake Oil. Don't flush it out.. leave it in the motor..the part ur describing sounds like the fuel cooler..

They were the STOCK ORIGINAL plugs from the factory (I bought the engine brand new) and replaced with OEM's from the Yamaha shop.

Their actually the folks that said it was a plug, which I found hard to believe with maybe 150 hours on the engine..



.Re flushing, I flush after every outing and use Salt Away. I know the SA DOES remove (at least on the outside) the majority of salt spray off the hood (just hosing initially).
I use muffs and the powerhead hose as well

I still have found a fair bit of corrosion after pulling the T-stat, internal anodes(in the head). AFTER seeing that, what I try to do (I have a boat lift, live on a canal),is when I come in T-stat STILL OPEN, hook up the garden hose (boats in the cradle, still running, t-stat still open) .

Hook up fresh water to the powerhead connection and run fresh water for a maybe 5 minutes (just to help keep the salt water deposits from "cooking" onto the block).
Once out of the water, it's run again on muffs for about 10. Then thru the power head with SA..


**That part (unk name) you referred to I suspect is the fuel cooler. Water flows in and out thru it with fuel adjacent (separate inside of course) and cools the fuel. You might have had some blockage (in the cooler) over time and the orifice kept closing over time/heat, added salt water clogging it up. I'd polk it clean, check/clean all hoses going to it...




**Where I'm at water can be salt water or brackish, depending on if their dumping fresh water from Lake Okeechobee (Florida) into the river and eventually into the canals. Brown/brackish water NO salt taste, salt, greenish, MUCH cleared-salty...

Rainey season (now coming to an end down here), they start slowing the dumping of brackish water.

.
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[Ducowti1]

Update:

Changed plugs out, and....no dice. Problem persists.

However, here's what I reproduced 3 times I tried this 'test': After a couple normal hole shots and running around 6000rpm (recall max is 6100), when it dropped rpm I shut the motor, primed the bulb, and she would hole shot and run normally, to 6100 (until she dropped again). When she dropped rpm and I shut the motor, NO bulb priming, restarted, the hole shot was abnormal/struggled, and she would max 5600rpm - I also reproduced this condition 3 times. So as far as I practically could, I was able to reproduce each of those conditions 3x, in succession, with no 'skips' between if that makes sense.

So, seems to me the issue is upstream of fuel/water separator at the stern/in hull.

Do you much-more tech-savvy lads concur, and what can I check from here?

Thx.

[99yam40]

yes it sounds like the VST is running low on fuel.
Try what Keith mentioned earlier(looking for air bubbles in the line) sucking air in.
Restriction or maybe the recirculation valve on lift pump side is sticking open and the pump cannot keep the VST full with all of the fuel being burned at high RPM

[Ducowti1]

I would run a foot or two of clear vinyl hose at the motor. Watch for air (bubbles) or hose colapse

Not following - mind elaborating Keith? Appreciate it.

[Ducowti1]

yes it sounds like the VST is running low on fuel.
Try what Keith mentioned earlier(looking for air bubbles in the line) sucking air in.
Restriction or maybe the recirculation valve on lift pump side is sticking open and the pump cannot keep the VST full with all of the fuel being burned at high RPM

The original VST seal (tank lid to base) looked in very good shape, and no corrosion around the edges of the tank mating surfaces so I didn't remove/replace it. Would that be a likely weak point to develop a leak? I now have that seal, can replace it, but want to be prepared w.comprehensive plan before taking it all apart again just to replace the seal.

[99yam40]

if you place a clear line in the fuel system at the motor, you should be able to see if air is being sucked into the system somewhere between the tank and the area you put the clear tubing

[Keithbaja]

LOL, now thats downright funny !! This captain has been called alot of things over the years, but never "mind elaborating" the outlet on your gas tank has a alumanan barbed discharge fitting. A 5/8 or 9/16 6 point wrench should do it. If the "block" starts to buckle/move put a 3/4 or 7/8 on that at the same time to counteract your looseing action. Turn valve upside down. With a punch or Phillips u can remove the ss ball and valve.. be advised,,I'm NOT telling you to remove the "problem child" I'm telling you how to only !! Also outboards that get my paws, go back to the owner with NO screw hose clamps except on the vent hose after the loop on the gunnel insides. USE Otiker clamps!! Zip ties with the rounded ends are suitable also. No f-ing screw
hose clamps if you want to do the job correctly...I'm stepping down off this soapbox !!

[Ducowti1]

LOL, now thats downright funny !! This captain has been called alot of things over the years, but never "mind elaborating" the outlet on your gas tank has a alumanan barbed discharge fitting. A 5/8 or 9/16 6 point wrench should do it. If the "block" starts to buckle/move put a 3/4 or 7/8 on that at the same time to counteract your looseing action. Turn valve upside down. With a punch or Phillips u can remove the ss ball and valve.. be advised,,I'm NOT telling you to remove the "problem child" I'm telling you how to only !! Also outboards that get my paws, go back to the owner with NO screw hose clamps except on the vent hose after the loop on the gunnel insides. USE Otiker clamps!! Zip ties with the rounded ends are suitable also. No f-ing screw
hose clamps if you want to do the job correctly...I'm stepping down off this soapbox !!

Keith, I haven't inspected for air leak since, despite your elaboration, I'm not quite following how to check. BUT, I did clean the injectors today; and the part you'll be happiest to hear about: my cut/repaired garden hose that services the boat has had a worm gear hose clamp on it for years. Always gets hung up on the brick, etc. I replaced that damn hand-slicer w.the otiker clamp from the set I ordered thanks to your counsel!

Will report back on whether injector cleaning had any effect, after I've run her again once the rain stops in a few days.

[Ducowti1]

Eh goddummit it wasn't the injectors. She holeshot strong, ran a hundred yards then sputtered a bit and lost the top end again. Guess I need dig into the air leak...