Mercury 250 Cutting out

[521rangerman]

Hello,
I have a Mercury 250xs SN 0T652483.
When I first start motor runs fine. Go to first place fish for say 30 min.Go to start and it will start but run rough or will reave up then die.Start again runs rough put in gear idle awhile and take off is fine.
Get to next place to fish kill motor and then restart and starts fine.
I always put fuel treatment Mercury Fuel Stabilizer/Treatment in tanks 10 gals at a time.
Any idea what it could be? Water in fuel, bad fuel, high pressure fuel pump?
Thanks for the help.
Tony

[EuropeanAM]

Tony- I'd recommend getting the Air/Fuel Pressures tested, and results recorded for:

-Idle
-Under Acceleration
-5/10/15 seconds after shutdown (restart for each).

Sounds like you're getting some un-metered fuel or oil into the engine.

Note: This can occur from something as simple as OVER-FILLING the remote oil tank.

[521rangerman]

I have never over filled the remote oil tank.
But I have noticed it seems I have to add oil to the remote oil tank more often. When it gets to about a gal low I add more.
Don't want to ever run out of oil.
Last time I talked to a mechanic about it he thought it was due to bad gas.
Thanks

[521rangerman]

My mechanic is a week out so I am going to test the fuel for water,check water separator if has one and fuel filter.
Anything else I can check on my own before taking it to mechanic? I plan on having my mechanic do a Air/Fuel Pressures test.
Thanks for the help.
Tony

[EuropeanAM]

Really need to focus around the basics, especially fuel quality, delivery, and proper Air/Fuel pressures.

Sounds like you're getting fuel into the engine from an un-metered source (combustible liquid from some source other than the normal pathway of injectors).

[521rangerman]

Spark Plug oil 11-14-2020.jpgSpark Plug Oil 11-14-2020.jpg.txt.PNGSpark Plug oil # 11-14-2020.jpg.txt.jpg

My mechanic agreed with doing a Air/Fuel Pressures test. But he is a week out. While I am waiting pulled cowling to look for leaks. None of the injectors had any leakage around them. But I did find oil around top right plug.

[EuropeanAM]

Spark plug was not fully seated and torqued properly.

[521rangerman]

My mechanic found the injectors had carbon build up.He sent off all 12 injectores to get cleaned and tested.He thinks it is due to back fuel.Engine has 600 hrs. I always use Don's Mercury cocktail QuickLeen,etc at every fill up.
Siad the injectors soaked for a week and were still dirty not spraying correctly.

[JOE54]

pay close attn to post #2 = you stated rev up on restart , recomend inspection of tracker valve and look for fuel in air side of system , pulse pump can cause it also,What is back fuel ???????

[EuropeanAM]

Maybe he was referring to "bad" fuel and spell-check got him.

[JOE54]

aaah good ol spell checker, report back RANGERMAN with resolution

[521rangerman]

Mechanic found all injectors needed to be cleaned were very dirty.Had all injectors cleaned and tested.
Found #5 Air injector was bad and #2 Fuel injector was also bed. Replaced both and boat idles and runs better than ever.
Not sure how they got so dirty. I always add Quickleen at every fill up.

[EuropeanAM]

A lot of factors can be at play there, including (but not limited to):

-Fuel quality/octane being run (vs. Octane requirement)

-Oil being used

-Both banks reaching Correct Operating Temperature (Thermostat function)

-RPM use profile (engine runs it's dirtiest at IDLE and WOT).

[521rangerman]

I knew idleing to much is bad for carbon build up but didn't know WOT was.
Don do you know about how much the air and fuel injectors cost each?
Thanks

[EuropeanAM]

Best thing you can do (aside from correct octane fuel, fuel cocktail, correct oil, ensure engine coming up to temp, and avoid excessive idling) is to make a nice long run in the 3500-4800 RPM range near the end of your outing.

That's the range where your engine gets it's best fuel economy- and also is where it runs it's "cleanest", too. Nothing wrong with running it WOT, as it's built for that. Just make a habit of making a cruise run to keep it as clean as possible.

On the injector question- I know exactly what they cost. We don't post pricing in the Forums as there's simply not enough hours n the day to chase down and reprice thousands of posts.

You can look them up on our website 24 hours a day- and when placed in the shopping cart, the latest part number and price is shown.

www.mercurypartsonline.net

[521rangerman]

Took boat out yesterday for few hrs, Starts fine runs great then about a hour later it starts runnning rough for a few minutes when first start. Let it smooth out, takes off fine runs fine. Going back today and docuement everytime it happens.And burn some gas thru the motor.Mechanis said had alot of carbon buld up. Seems to happen when it warms up.

Second day ran boat.
Made run 4500 RPM's for about 10 minutes.Stopped to fish for 20 min tried to start and rough idle died the restarted let run till it smoothed out about 2 min.
Had great hole shot and ran great.

Problem seems to happen after you make a run kill the motor and try to restart after 20 min or more.And you can smell gas from motor when you first try to start it again.

[EuropeanAM]

...Stopped to fish for 20 min tried to start and rough idle died the restarted let run till it smoothed out about 2 min.
Had great hole shot and ran great....

Problem seems to happen after you make a run kill the motor and try to restart after 20 min or more.And you can smell gas from motor when you first try to start it again.

Need to get the Air and Fuel Pressures checked, and results recorded for:

-Idle
-Under Acceleration
-5/10/15 seconds after shutdown (restart for each time period).

Also, make sure you are pumping the bulb firm before EVERY engine start (not just the first start of the day).

You'll note this is the same advise that has been given previously in this thread. Until (and unless) you get someone to LOCATE the source of un-metered fuel or oil into your engine, this will continue.

See Posts 2, 3 and 9 (above). Also note that an internal leak in the PULSE PUMP (mechanical fuel pump) can also be a source of un-metered fuel.

[521rangerman]

Problem is fixed. Mechanic had it finally fail on him. The Air Pressure gauges needle started bouncing and started running rough. You had to start it let it run till warm then kill motor let set for 20 minutes.
The Tracker Valve was bad.
Tracker Valve readings: Spec show fuel=air +15
Before- Air/Fuel PSI 96/103
After- Air/Fuel PSI 96/110
Thanks Don and everyone for your help.

Attachment 447025

[EuropeanAM]

Tracker valve doesn't actually have "readings"- it's just a device that absorbs spikes in the pressures.

The air and fuel PRESSURE regulators are what "control" the pressures (though a severe leak in the system, such as the tracker valve, could cause incorrect or irratic readings).