@Way2slow you're cooking with gas now bud. 

 

Soot on the plate. Shined a flashlight down in the cavity and I can see a pool of clean blue oil laying in the bottom.

 

I tried getting a photo of the pool of oil inside, but can only get a phone and flashlight so far in. Lol

 

So any thoughts on what could cause this? Id love to fix this myself. But not sure if this is beyond my limits yet and best of taking to a mechanic. 

 

So prior to finding this, earlier this year when I was getting boat ready for the year I found that the oil pump had a minor leak. Doing research I found it was a common issue. Early on in these motors the fix was to replace the whole pump. Now people have taken them apart and have found the culprit to be a .50 cent o ring failing inside. Possibly this would be the cause for this issue as well? 

Not sure what pitch it's supposed to go but id say it hits 80 degrees

You can't tell much about how it's burning once it has idled, most all two stroke motors are going to carbon plugs when idling.  That's why you do what's called a plug dump, the WOT run and shutting it off or pull the kill cord.

The butterflies should be going perfectly horizontal.  80% open means that's 20% of pedal response that's not being used.

It also makes a difference if you index your plugs.  I never install plugs without indexing them.   Some manufactures make different thickness compression rings, if they run them.  For those that just run a tapper seal, it takes have a couple set of plugs to work with.

Looking at the carbon and what you describe you are seeing, it sounds like you have an over oiling problem.

Now, you are getting into no mans land for me.  I don't know crap about Mercury motors.  I can build you one hellava OMC, but have not done much with Mercs since the early 70's.

If have one sitting in front of me, I know motors well enough I can fix most anything one can throw at me, but, to be able to tell you what or how, since I've never seen your motor with the cover off, I can't offer much specific help.

 

One other thought, I think that motor runs carbon fiber reeds.  Those have a tendency to have a little extra blow back.  Reed valve motors are going to have a small amount of blow back through the carbsl

Okay maybe a weird question. Or maybe it isn't, but im not sure.

 

But could a undersized battery cause the issues? 

 

I've been going through manual and doing research online. An I just realized I've been running a very undersized battery. It calls for a 800 cca or 1000 marine cranking amps, an the one I've been using is way under that

Once it's running, you should be able to see what the charging system is doing by the volt meter.  It should have over 13.6 volts when running at about 2,000 rpm or more, so the battery would not be causing a problem.

Where the under sized battery will get you in trouble is on a cold morning.  When you try starting the motor, it may crank over but the voltage drop can be so great, the ignition system may not fire.  It will also run down very quickly when trying to crank it.

Okay...woooh  woooh....

 

Compression on that motor should be in the 105-120 range.  I know you said you did not warm it up but I have never seen one gain 15-30 lbs once warmed up and some will say a two stroke should be done cold.  I my humble opinion I would do both.  When cold pull all the plugs at once and do each cylinder as you do not want the cylinder you are testing to be impacted by the others fighting compression.  Put the plugs back in and warm it up on muffs.  You don't really have to run it to long you just want the cylinder and piston good and warm which happens well before the exhaust/pee water gets warm or the thermostat even opens.  In a perfect world you do this at the lake where you can get it to full operating temp.  You do not want a huge diff in cold and hot compression.  Really getting it hot is where shows or can uncover the old trick of squirting a little oil in a bad cylinder to get it to test good cold.

 

The plugs really do not look that bad.  Any idea how many hours on them?  I really think any issue you would have had with the motor to cause this would have alarmed on your gauge.  Those motor monitor everything from fuel pressure, to misfires, and about anything that can impact how it runs.  It has a "Guardian" mode where it will limit RPM's if it senses an issue.  This all works in conjunction with the SmartCraft gauges.  If you get a single important engine sensor out of range it limits the RPM's.  Those motors have some failures in the VST pump but again that will surely throw a fuel pressure alarm.

 

https://www.perfprotech.com/blog/marine-outboard-motors/mercury-marine-smartcraft-and-guardian-system-warning-horn-alarms

 

If you did not pull all the plugs for compression test do that and see what you get.  If you get numbers like I would expect (110lbs */- 5) then get the 25p and run that prop to pad up to 3.5".  Maybe @ 4.5 it was just terrible combo of slip and lack of bow lift.  I would expect the 22p @ 3.5" would blowout.  22P push a lot more water up and around the prop than a higher pitch will.  The higher the pitch normally the higher you can run the motor because the pitch pushes a greater volume of the water back.  You will see guys with Bullits and Alisons running 2" but that also has to do with those being very light boats.  I have a buddy with a Skeeter 21I with a 300 and he is at 2 1/4".

On 4/2/2020 at 7:45 PM, FordsnFishin said:

Okay maybe a weird question. Or maybe it isn't, but im not sure.

 

But could a undersized battery cause the issues? 

 

I've been going through manual and doing research online. An I just realized I've been running a very undersized battery. It calls for a 800 cca or 1000 marine cranking amps, an the one I've been using is way under that

 

I doubt it.  That is for sure one of the things that the SmarCraft stuff will fault on.  V has to be between 10 and 16 according to the ref link above but I expect more like Way2Slow said... once running you will see mid 13v about like any car alternator also.  Those motors need a huge amount of cranking amps for the starter and to get the pump spinning in the VST.  That starter is a beast as it is fight 6 cylinders of very beautiful 2 stroke power.

 

 

Total guess but from the looks of the plugs and intakes did the previous owner do a lot of idling or low speed I wonder?  Looks like the saltwater two stokes from the coast down here.  They idle and troll all day and wonder why they have carbon build up and run like crap.

 

 

I don't get too wrapped up in compression numbers being lower than normal.  That could be caused by a difference in gauges or other things.  The readings being within 5% is the critical part.  That's why I prefer doing a leak down test over compression test.  One thing people tend to over look, doing a compression test on a two stroke, the throttle plates should be fairly open so the motor can get the air it needs to give a proper compression.  Granted, it's better and has a better indication of motor condition if it has been brought up to operating temp before doing a compression test.

When I do a compression test, I warm the engine, open the throttle at least half throttle, and let it hit the same number of times on each cylinder, six hits is my magic number I use.

@Way2slow @imbatman

 

So compression while cold was all 90. Today I put plugs back in and let her run for approx 2-3 minutes to warm up. I opened up the butterfly valve partly during test. Pulled plugs and ran another compression test.

 

Everything checked out at 90-91 lbs again. Cylinder 6 plug looked a bit wet as I pulled it. I dunno, maybe it is my gauge that is off? Im happy to see that at least they all read the same. 

 

What you guys said about the battery makes sense. Was just something I read and noticed, just didn't want it to be something I overlooked. It's always started right away, and while running typically maintains around 14.4 volts. 

 

I've never had the cover off while running it. Luckily I did this. As I noticed a water leak pointed by my finger in photo. Actually prior to running it, I noticed water spots on the motor in this area but just figured it was from the lake. 

 

The guy I bought it from did do alot of idling. Lake Barkley and Kentucky . However I have owned this boat 2 years now, I do a fair share idling around looking at graphs. Most of my high rpm runs don't last but 2 minutes, and at most 10 minutes. I've always ran stabil 360 marine in the fuel. What can I do to help fight carbon? 

 

@imbatman not that I'm doubting you but when I tested the 25p @ 4.5 prop to pad and took it down to 5.5 and it did better. Wouldn't you think it would have done the opposite if taking it to 3.5 would do best? Sorry if that's confusing.

 

I agree the guardian monitor system on these seem pretty legit. Thankfully it's only warned me once. Been running through shallow muddy water and had a constant horn telling me overheating. Found a little rock had gotten sucked up and blocking pee hole.

 

I also tried indexing the plugs. Of course only 1 of 6 would get into the "good" zone. I did try swapping around with no luck. Thought I read somewhere you can get indexing washers, which would allow you to change thickness to get them where needed? 

The Pee hole has little to do with overheating,bthat is either the water pump impeller, probably low water pressure (under 10 psi) or a thermostate issue. The way water cooling works is the power head needs to warm up before cool water is let in via the thermostate. The pee hole simply indecates the water pump impeller is working but doesn't indicate pressure or if the thermostate is open.

Tom

 

These are all just opinions but it comes from a lot of experience.

 

Be careful doing leak downs on two stroke as you will blow crank seals.  Very low PSI should be used with great care plugging the ports.

 

For the compression maybe it is the gauge but I would have a 2nd gauge on it to verify.  I would not trust a gauge that reads 90 on a cylinder that has 110.  It would have been very easy for someone to have replaced those head gaskets at some point and used the wrong thickness.

 

I was a really lucky guy for a while.  I worked in a boat shop (Collinsboating.com) for a while doing service and rigging and got to use a bunch of bass boats.  Basically if we got a used boat in on trade and it had a Yama or Rude on it I could take it out or if it had warranty left.  I drove about every brand bass boat in a 20 or 21 and they all do 70mph with a 250.  They all turned at least a 25 pitch prop. 

 

This is a Ranger Z521 I used a bit.  It is one of the heaviest, if not THE heaviest bass boat hull on the market.  Rangers are great riding but not know for their speed.  It would run 72-74 all day long.  We had a Triton Tr21 with the same motor you have and it ran 76mph.

 

Something is not right.  One thing is for certain with no doubt.  The 250 Pro XS should bury that 22 pitch prop into the reve limiter without much problem,  I am not saying do it but a correct running 250 on a 1500lb bass boat should spin a 22 off the darn prop shaft.

 

This was out at Falls Lake in outside Ral NC a couple of years ago.

 

 

imbatman. I guess I missed something in your leak down test and not understanding what you are doing.  The only leak down test I know of is using a special leak down tester that screws into the spark plug hole.  It has two gauges on a manifold with a .040" orifice between them.  The Crank is locked into position at TDC and 100 psi of pressure is applied (tester usually has s small regulator on it to set it to exactly 100) and read on the first gauge, it passes through the orifice into the cylinder and the second gauge reads the pressure that's on the cylinder.  If there is zero leak down, the cylinder side will also have 100 psi, but that ain't gonna happen, there is always some bypassing the rings.  Anything below 95 psi on the second gauge 5% blow by is considered to be not very good, it it's at 90, 10% or worse, its considered a motor ready for a rebuild.  Now, the crank does not have to be locked, if it's on absolute TDC, it will stay there, but if it's off even a micro amount, the piston is going to fly to BDC when pressure is applied.   I believe you are thinking about how to pressure the crankcase, which is a totally different animal than a leak down test.

 

As a for gauges, I've seen too many times someone replaces the Schrader valve with something besides one with the white band around it,  and see very low numbers or the Schrader valve just be bad.  I've seen these Harbor Freight gauges have gauges on them that were 20 or more pounds off.  The gauge itself can be easily be tested by comparing to a known good gauge but the Schrader valve (the one inside the end that screws into the spark plug hole) can only be tested by replacing it with a new one, WITH THE WHITE BAND.  Those only require less the 10 psi to open them, the blue ones like found in car tires require as much as 30 - 40 psi to open them.  The white band ones can usually be found on most of the MATCO or Snap-On tool trucks.

 

Now, if you are 100% positive your gauge is accurate, and you are only letting it hit about six times on each cylinder and you are coming up with 90 PSI, you have a major problem.  I've never seen a motor wear out so evenly that all six cylinders lost compression that equally.  Usually, you will see as 10% or more fluctuations between them.  

Since I don't work on Mercs, I don't know what that motor should run, but I know on my DFI Evinrude it runs about 128psi compression.  

Since the fuel injected motors have a very good computer control system on them, they can safely run a lot higher compression than the old carb motors from back in the late 80s and early 90's. 

So, my first check would be if they offered different thickness head gaskets for your engine. If they do, I would consider getting a set of the thinnest set available and swapping them out. 

 

FordsnFishen, if your plugs run the compression rings, a lot of the speed shops sell indexing compression rings.  They usually have about three different thickness, in each set, but some tend to be just a little bit proud of them.  Just make sure they are the diameter that fits your plugs.  If they are close, you can get away with just slightly over torqueing them but understand, I said slightly, you don't want to be stripping out no plugs holes.  Unless they are extremely expensive plugs, I usually just buy about three sets and can usually find enough that will index properly.

The 250 Merc should be 110-120 psi (115 nom), 90 psi is about 25% low! This engines computer can provide a hours use at various rpm's, the OP should get a service record and hours print out.

Tom

Another thought, since that motors has a pretty good track record of long idle periods, I would do some serious decarbing. I would get about four cans a do it twice.  I would use two cans at once, one on each side, quickly going up and down each side of the intakes with motor with enough to just barely let the motor run with some pretty good throttle applied.  As the cans get low, give a big dose, enough to choke the motor down.  Let it sit over night, and do it again, letting it sit another night or so.  Then take it to the lake and make a WOT run for a few miles.  When you get back home, throw a new set of spark plugs in.  If you have recently replaced the  plugs, put an old set back in to do the decarb, the put the new ones back in after the WOT run.  

Just be aware, if you have neighbors, they are not going to like you, but you will probably chase every bug within five miles away because of the major amounts of smoke.  Don't do it over your paved drive either, unless you have something to catch all the black crud that is going to drip out of the exhaust.

@Way2slow cans of what? Im confused where you're saying to spray it? 

 

I did approx a 3 min WOT run yesterday and pulled the kill switch. About to pull plugs now and will post results. 

After doing the WOT test appears they're burning pretty well. All seem pretty identical. 

Im going to barrow a buddy of mine compression gauge just out of curiosity and see. Mine is a cheap one so I'll just about bet it's off. Especially with the numbers I got out of mine. 

 

Something like this https://www.basspro.com/shop/en/quicksilver-power-tune.  It's sprayed in the throttle bodies.

I wish I had more experience with Merc's because not having it, makes me a little leery on expressing my opinion.   If that was one of my engines, I would say they are way too dark around the lower part of the insulator, but that may be totally normal for that motor.  I would suggest posting that picture on Scream and Fly and asking them.  Tons of Mercury gurus on there that can offer a whole lot more help that me.  https://www.screamandfly.com/forumdisplay.php?20-Technical-Discussion

What plug are you running? I believe the 250 XS uses Champion IZFR J6's @ .042 gap.

The plugs look OK color just tired. Can't judge the gap? it looks excessive.

Tom

 

Won't Leak down testing a 2 stroke pressurize the crankcase @ TDC as the intake port is not covered.  You put 100 psi in a 2 stroke with the piston at TDC and you will blow the crank seals want you.  The intake and exhaust valves are closed on a 4 stroke so it is sealed at TDC but not on a 2 stroke as it is still pulling the fuel charge at TDC.

 

I have always done it at bottom dead center so the intake port is closed then you have the seal the exhaust port with a rubber plug or the like.  I worked on more 2 stroke bikes than boats (plenty of boats) but the 2 stoke fundamentals are the same aren't they?

 

" With all test equipment in place and the piston at bottom dead center, use the hand pump to pump 6 PSI of air pressure into engine. Never exceed 8 PSI of air pressure or damage to the seals and/or engine may occur. "

 

https://www.motionpro.com/a/2-stroke-leak-down-tester-08-0071/

 

 

http://www.animatedengines.com/twostroke.html

Not sure what kind of two stroke you might be referring to, but all I have ever worked on, it would be impossible to get a reading at BDC.  The exhaust port is wide a** open and there is no way it's going to build any kind of pressure with all the air going straight out the exhaust.  If there is enough blow by on the rings that you pressurize the crankcase doing it at TDC, then it wouldn't matter anyway, the engine is so badly worn, it needs rebuilt anyway.  However, I don't think a .040" orifice could ever hope to pass enough air to pressurize the crankcase even if you have perfect seal on the reeds,  There's enough blow by on the crankshaft seal rings to bleed it off, and the siphon valves would pass more than that small of an orifice could ever hope to deliver. 

 

What you have referenced to is crankcase pressure testing.  They are referring to as a leakdown, but that's of the crankcase, not checking piston ring condition.

 

I think you have dug a whole into something you know nothing about and trying to dig your way out again.

I am not here to argue over anything. All I can do is ref you to the link I supplied.  

 

If you have a link to pressure testing a 2 stroke with 100 PSI or more I would be more than happy to read it. I have an open mind as we all learn things most days.

 

The issue using such high pressure is that if you have a scored rings in the piston or piston walls the leaked air goes into the crankcase where you have rubber seals on the end of the crank.  To much pressure (ie 100psi) and the seals are gone.  You can use 100psi on a 4 stroke because the crank case is not part of the fuel charge system as it is in a 2 stroke and if your rings are so far gone in a 4 stroke then you would have blow by and get fuel mixed into the crankcase oil.  That is what happened with the first yamaha 4 stroke SHO's.  You would go to change the oil and it would have more "oil" in it than was put in.  Type into to google "yamaha outboard making oil".

 

As far as the exhaust port being "wide a** open" that is why you have to plug them... as ref'd in the article.

 

 

Like I said, you don't have a clue as to what you are talking about when it comes to doing a leak down test on the cylinders in an outboard motor.  You are still trying to use your references for pressure checking the crankcase on a motor cycle.  I would luv to see you trying to plug the exhaust ports on most any outboard, much less something like a big V-6.

I'm not trying to be argumentive,  I just don't like someone posting bogus info and someone reading your post to think it's right.  As I keep saying, crankcase pressure testing is a totally different animal.  It's not even possible to pressurize the crankcase doing a cylinder leakdown test.

So you have worked as a rigger in a boat shop for a short time, I have built, modified and raced outboards for almost 50 years and know a number of very well known engine builders and have never heard of an engine being damaged do a leakdown test on the cylinders.  With 50 years experience and doing untold number of leakdown test, and knowing of others that account for thousands of cylinder leakdown test being done is all the verification I need.

Oh, and just for gee wiz, check out this U-tube and a dozen more like it if you do a search.

 

I deleted the one on the Yamaha 225, didn't notice it was a 4 Stork.  

Also, the gauge they are using works a little different than mine but serves the same purpose, theirs you pressurize and balance first and reads direct percent.  My old style one, I pressurize to 100 psi on the first gauge so each pound of drop on the second gauge is one percent.  Theirs the input can be less than 100 because it's reading differential pressure.  Both systems are using high pressure, you just read them different.

The first comment in that video questions what they are doing. The second comment indicates it is not a 2 stroke by asking if this would apply to a two stroke.  I tried to verify what they are actually testing but the link they supply does not work for the details on the test.  The website is dead (boatinglocal.com) even.

 

So help me then.  If I am at TDC of a 2 stroke, have a broke ring and put 100psi to it you do not believe it will pressurize the crankcase and blow the seals?

 

As far as "not having a clue".  Did that make you feel better?  Get some endorphins popping?  It's kinda like crack to some folks.  The internet amazes me because you find out how people really think about themselves and others.  There is an old saying that integrity is about what you do when no one is looking.  I have seen this in comparison to folks lack of manners and civility on the internet when no one knows who they are.  

 

 

 

 

 

 

You obviously know absolutely nothing about a two stroke engine and are ungodly hard hardheaded.  I don't care if there is even no rings or even a piston in the cylinder, IT IS NOT POSSIBLE TO PRESSURIZE A TWO STROKE ENGINE CRANKCASE FROM THE SPARK PLUG HOLE DOING A CYLINDER LEAK DOWN TEST. 

 

I'm done, have a nice day.