200HP carb issue?

[iltfish]

I have a 1999 200 HP Saltwater Series II carbed OB. Recently, I am only able to make 4700rpms at WOT when before I was at 5300rpm consistently. It then began to lose still more rpms and surge. If I leave the throttle WOT, the engine will wind all the way down and stall. If I retard the throttle, it will not stall but just lose rpms to a certain point and then stabilize. I then can advance the throttle and accelerate again for a few seconds and then it will start to decrease again.
I have checked and replaced all plugs, replaced all filters, compression tested each cylinder, and even ran the engine on an external 5 gallon gas portable tank with no success. It seems to get worse as the engine gets warmer. I just pulled the boat for the season and want to fix it soon. I have spoken to a few local reputable shops and their suggestions are all over the board from rebuilding carbs, replacing fuel pumps, power pack, or some type of ignition issue. By the wide range of their response, it appears to me that they may have no idea and will end up costing me alot of money in "shotgun" troubleshooting by replacing parts. BTW, I rebuilt carbs and replaced fuel pumps in 11/2005.
Any ideas on this problem would be appreciated! I would rather troubleshoot myself than pay a shop to guess at $105/hour. Thanks :?:

 

[Paddleon]

Fuel pumps are fairly inexpensive and very easy to replace yourself.But it doesn't sound like a fuel pump issue.
To me it sounds like the carbs are the problem and I would rebuild them/have them rebuilt.I've just gone thru a similar situation as yours and...its the carbs and the damn ethanol stuff playing havoc with these Yammy carbs.

 

[Megabyte]

Given the symptoms, I would suspect the fuel pumps or carbs too, but you say that you rebuilt the carbs and replaced fuel pumps in Nov of 2005.

You also eliminated a fuel vent or anti-siphon problem by running on a portable tank...

The surging that you mention is typical of an O2 sensor that is dirty or no longer working, but I'm not sure if the carbed motors have an O2 sensor. The EFI SWS-II motors have them, but not sure about the carbed motors. Do you have a VST filter?

Curious... I'd take another look at the fuel pumps and carbs, along with the O2 sensor and VST if it has one. The symptoms are certainly consistant with a fuel delivery problem.

 

[John_Madison CT]

No O2 sensor on the Carb'd engines.

 

[iltfish]

No VST filters on carb'ed engines either.

 

[Megabyte]

Well that shoots my theory(s).
Back to carbs and fuel pumps?

 

[gw204]

Whatever route you choose, do the cheap and easy stuff first. In my book, that's those 3 fuel pumps. I did both of my 225s earlier this year in 2 hours.

Where did you hook that external tank in?

 

[iltfish]

I hooked up the external tank to the primer bulb inlet after disconnecting the ship input line and plugging the end. This isolated my tank, water separator, and flowmeter.

 

[DaleH]

It seems to get worse as the engine gets warmer.

I have spoken to a few local reputable shops and their suggestions are all over the board from rebuilding carbs, replacing fuel pumps, power pack, or some type of ignition issue.

I'll agree that intermittant electical problems can be the most difficult and expensive to repair.

Have you taken a look up under your stator? Use a flashlight and look for any black goop to be dripping down off from around any of the windings. If you do - that ain't good, but you probably just found the culprit!

A worsening problem with a getting warmer engine typically means an electrical component is breaking down with heat.

I would do this:

When happening, immediately SHUTDOWN and pull the plugs. have someone else throw the anchor overboard. Look at your plugs, if one looks 'cleaner' than the others that I'd opine that its coil is breaking down, thus it's not firing and providing RPMs, but the fuel is still being delivered so that plug is being washed. It may show as being cleaner or wetter than the others.

If you suspect this, SWAP that coil to the same plug height on the other side of the V-bank, but put the plugs back into the same holes. Now see if that other plug on the other side of the motor nows looks 'washed'.

Otherswise, I'd suspect something in the primary ignition circuit and my 'best guess' would be the stator. Usually with powerpacks on carb'd motors, the high-speed end of the circuiit goes and your RPMs would be cut off constantly at a lowered RPM limit, one not depending on throttle position or warmth of the engine, from my experience anyway.

 

[gw204]

You could have a primer bulb and or fuel line that's failing. Does the bulb stay nice and hard all the time? If not, replace that stuff with OEM. It's cheap too.

Don't use the generic ones. They're crap.

 

[goinsfishin]

I think I'd start with the fuel pumps, those diaphrams can wear pretty quick and as noted its an inexpensive replacement.

 

[iltfish]

DaleH,

The boat is out of the water for the winter now, so my troubleshooting abilities are a bit limited now. I did take a look under the stator like you suggested. I did not see any black goop dripping from the windings, but there is some type of black stains on the varnish on the windings. Is this some type of insulator and is this normal? I have really not looked under there before to notice anything out of the norm. At any rate, it is not dripping down, but just stained on the windings varnish.
Thanks

 

[iltfish]

To all involved, I have placed the boat in the water today and I still have a problem. The engine is not revving down anymore when WOT, that turned out to be the fuel pumps. I can still not make full power. I make 4700r's and not the 5300/5400 that I used to make. Here is what I have down over the winter. I rebuilt the carbs, replaced the fuel pumps, fuel filter, water separator,fuel lines, spark plugs, and stator.Also, when in neutral at idle, I have gas being spit out the exhaust.I suspect it does it while in gear, but it is tough to determine.When in gear in idle, the engine sounds rough, but not like a miss and definitely no knocking.All cylinders are equal temperature during and after running for a while.I am beginning to think that the spark rate is not fast enough or the spark length is not sufficient. I am going to recheck the gap on my plugs tomorrow am, but I am sure it is good.I am at the point where this will start getting real expensive; pulser coils, ignition coils, ECU, etc... and need some advice. I have spoken to my two local Yamaha shops and they are puzzled, but if I bring it in to them they will be glad to fix it. My opinion is that they will systemically replace parts until it is fixed and cost me a fortune.I am reaching out to the group for any troubleshooting tips or suggestions. I will be on the boat tomorrow morning, so any help is appreciated. Thank you!

 

[Paddleon]

I went thru something similar last fall.If you track down my old posts you'll come across it.
I replaced alot...
and it was the carbs!

Its the carbs for you also more than likely!
You rebuilt them but now they need to be synchronized and adjusted.
With everything you've replaced I would think a reputable mechanic would be able to adjust everything in fairly short order...an hour or so.
I'd spend the $105 and let a marine guy get it done.


Let us know what the end result turned out to be!