# How to test for dropped cylinder?



## Dillusion (May 21, 2012)

What I thought was a fuel issue previously is looking more like one of my cylinders is going out when the outboard heats up.

Yamaha 50 2-stroke 2004

From 0-3900 RPM the outboard runs just fine. From 4000-4900RPM the motor will for no reason while running drop to 4000 RPM and 10-20 seconds later jump back up to 4900RPM. When running over 4900RPM the motor does it, but less frequently, I think. WOT is 5300 RPM.

The outboard has brand new fuel lines, brand new fuel filter assembly, brand new QD sockets, brand new fuel pump, and the carbs were just rebuilt. This leads me to believe something in the ECM/ECU/PowerPack/Stator is heating up at a certain temp and expanding, or one of the coils is going bad or also having trouble with the heat.

How does one go about testing this at home? I could test it out on the water I guess, and bring a spark checker with me and somehow look backwards at the motor while running? lol Or I can bring my digital MM with me while out on the water and do some voltage measurements when the outboard gets hot from being at WOT- but I can't do any of this on the hose at home.

Is there ANYTHING I can do at home to diagnose it while it's warmed up from idling?

I am going to unscrew the bowl screws in my carbs tonight and bleed out whatever is in there and see if there is any sediment in the bowls warranting another carb clean...but I doubt it.


----------



## rkmurphy (Nov 2, 2008)

Go to Harbor Freight, buy yourself a $10-$15 compression tester, and report back. Hope it's nothing serious! I probably need to do this, as well...just for my own comfort.

Have you badly overheated it? That Yammy 2 stroke shouldn't be giving you trouble like that!


----------



## danville_marine (Jan 24, 2013)

use a timing light have some one watch while u run it see if light quits firing


----------



## Dillusion (May 21, 2012)

> Go to Harbor Freight, buy yourself a $10-$15 compression tester, and report back.  Hope it's nothing serious!  I probably need to do this, as well...just for my own comfort.
> 
> Have you badly overheated it?  That Yammy 2 stroke shouldn't be giving you trouble like that!


Compression is fine, 90 on all cylinders with my cheap gauge.

It hasn't overheated, it has an overheat alarm. If compression was bad it would be bad all the time, not intermittent. Though I could see hat your saying as the metal expands in the cylinders it could cause problems, but it's not a compression issue.


----------



## rkmurphy (Nov 2, 2008)

Is it just me or does 90 seem low? My knowledge is pretty limited here...


----------



## Dillusion (May 21, 2012)

> Is it just me or does 90 seem low? My knowledge is pretty limited here...


90 is 'low', but it's a cheap gauge and with a proper one it would probably register 110-120 like it should. When checking compression looking to see if all cylinders are within range is more important that what the actual # is...unless they are all saying 50psi lol than thats a problem.


----------



## HaMm3r (Dec 11, 2006)

Any chance it's ventilation of the prop that's causing the RPM fluctuations? Perhaps if you're running the prop close to the surface it's ventilating a bit, then all of a sudden it gets a little more bite and RPMs drop until it begins to slip again. That would explain why it does it less at WOT, since you'd be running higher on plane, thereby farther above the slip/grab water level.

No idea how your motor is mounted, but if you can trim it down farther and test again, it might save you some headache.


----------



## TwoKids (Jan 2, 2013)

I like keelme's idea, I gotta remember that one, smart thinking. I have heard cut and creek say yammie electrical systems are rock solid more than once though. If it were mine just for the heck of it I'd complete a shock of ring free or seafoam then change the plugs just as a little preventative maintenance if nothing else and you never know you may get lucky and free something up. Many people swear by that stuff and Yamaha recommends it.

Not to get off topic but just curious, what kind of oil are you running and do you premix or is it injected?


----------



## Dillusion (May 21, 2012)

> I like keelme's idea, I gotta remember that one, smart thinking.  I have heard cut and creek say yammie electrical systems are rock solid more than once though. If it were mine just for the heck of it I'd complete a shock of ring free or seafoam then change the plugs just as a little preventative maintenance if nothing else and you never know you may get lucky and free something up. Many people swear by that stuff and Yamaha recommends it.
> 
> Not to get off topic but just curious, what kind of oil are you running and do you premix or is it injected?


I already use yamaha ring-free every other tank of gas.

I am not pre-mixing, I am using yamaha 2-M 2-stroke oil in the oil tank.


----------



## Dillusion (May 21, 2012)

> Any chance it's ventilation of the prop that's causing the RPM fluctuations? Perhaps if you're running the prop close to the surface it's ventilating a bit, then all of a sudden it gets a little more bite and RPMs drop until it begins to slip again. That would explain why it does it less at WOT, since you'd be running higher on plane, thereby farther above the slip/grab water level.
> 
> No idea how your motor is mounted, but if you can trim it down farther and test again, it might save you some headache.


If it was slipping, my RPM's would go up- not down. I thought of that too and I am getting a cup put in my prop this week.


----------



## TwoKids (Jan 2, 2013)

> > I like keelme's idea, I gotta remember that one, smart thinking.  I have heard cut and creek say yammie electrical systems are rock solid more than once though. If it were mine just for the heck of it I'd complete a shock of ring free or seafoam then change the plugs just as a little preventative maintenance if nothing else and you never know you may get lucky and free something up. Many people swear by that stuff and Yamaha recommends it.
> >
> > Not to get off topic but just curious, what kind of oil are you running and do you premix or is it injected?
> 
> ...


I was thinking going with a serious shock treatment dosage, 2oz/gal If I remember correctly... assuming you have never done a super clean since you bought it. Standard every other tank PM type dosage is good to prevent buildup but if was already gunked prior to you buying it then the light dose prob wouldn't cut the performance robbing nasty stuff. Good luck to you with the troubleshooting, hope you can get it fixed, chasing ghosts is frustrating, been there...


----------



## Dillusion (May 21, 2012)

> > > I like keelme's idea, I gotta remember that one, smart thinking.  I have heard cut and creek say yammie electrical systems are rock solid more than once though. If it were mine just for the heck of it I'd complete a shock of ring free or seafoam then change the plugs just as a little preventative maintenance if nothing else and you never know you may get lucky and free something up. Many people swear by that stuff and Yamaha recommends it.
> > >
> > > Not to get off topic but just curious, what kind of oil are you running and do you premix or is it injected?
> >
> ...


Already did a shock treatment when I got the motor.


----------



## TwoKids (Jan 2, 2013)

Got some time and wear on those plugs yet where you can inspect for any deltas between them?


----------



## DuckNut (Apr 3, 2009)

> 90 is 'low', but it's a cheap gauge and with a proper one it would probably register 110-120 like it should. When checking compression looking to see if all cylinders are within range is more important that what the actual # is.


From my knowledge this is somewhat accurate. Correct, that consistency is vital. But why would an expensive gauge read 30% higher?



> Compression is fine


To get accurate numbers it is important to check when the engine is warm, not cold.



> If compression was bad it would be bad all the time, not intermittent


Not gospel. Your compression can vary drastically between cold and warm as well as idle vs. speed and no load vs. load.

Although it does not sound like a piston problem because the rpm's come back, can't rule it out. It does sound more like an electrical or intermittent fuel starvation.

Since there only a few wires, can you test the resistance. Also- check the plug wires for resistance - not sure if yours are integral to the box or not.

How did the fuel re-check go?


----------



## Creek Runner (Sep 1, 2011)

Your issue if you are describing it right does in fact sound like an electrical issue. Does it do it every time you go out? You can use the timing light as pointed out above to determine if you have a spark issue keep a close eye on the light it may not just quit firing but start missing. You can not check the entire firing systems with out some special tools. But you can check some, I think I remember you saying you had a manual in it will be the procedures to check the components you can. Let me know if you need any help. 


Standing by
Creek


----------



## Creek Runner (Sep 1, 2011)

> > 90 is 'low', but it's a cheap gauge and with a proper one it would probably register 110-120 like it should. When checking compression looking to see if all cylinders are within range is more important that what the actual # is.
> 
> 
> From my knowledge this is somewhat accurate. Correct, that consistency is vital.  But why would an expensive gauge read 30% higher?
> ...


90psi is low, and I have used $15-$300 gauges and have never had a gauge read 25-30psi low unless it was broke. But I don't think it has anything to do with your current problem. It also may come up once you run it for 10 or so hours as I think I remember you saying the motor sat for a long period of time. 

Standing by 
Creek


----------



## HaMm3r (Dec 11, 2006)

> > Any chance it's ventilation of the prop that's causing the RPM fluctuations? Perhaps if you're running the prop close to the surface it's ventilating a bit, then all of a sudden it gets a little more bite and RPMs drop until it begins to slip again. That would explain why it does it less at WOT, since you'd be running higher on plane, thereby farther above the slip/grab water level.
> >
> > No idea how your motor is mounted, but if you can trim it down farther and test again, it might save you some headache.
> 
> ...


Read what I wrote again...you're interpreting it exactly the opposite of what I was suggesting.


----------



## Dillusion (May 21, 2012)

> > > Any chance it's ventilation of the prop that's causing the RPM fluctuations? Perhaps if you're running the prop close to the surface it's ventilating a bit, then all of a sudden it gets a little more bite and RPMs drop until it begins to slip again. That would explain why it does it less at WOT, since you'd be running higher on plane, thereby farther above the slip/grab water level.
> > >
> > > No idea how your motor is mounted, but if you can trim it down farther and test again, it might save you some headache.
> >
> ...


So you're saying it's the opposite...? I'm slipping all the time, and only 'biting' when the RPMs drop?


----------



## Dillusion (May 21, 2012)

> Your issue if you are describing it right does in fact sound like an electrical issue. Does it do it every time you go out? You can use the timing light as pointed out above to determine if you have a spark issue keep a close eye on the light it may not just quit firing but start missing. You can not check the entire firing systems with out some special tools. But you can check some, I think I remember you saying you had a manual in it will be the procedures to check the components you can. Let me know if you need any help.
> 
> 
> Standing by
> Creek


Yes it does it every time I go out.

I do have the manual and will be reading it today in the electrical chapter.

I wanna get this fixed so I can sell the damn boat with a clean bill of health ;D


----------



## Creek Runner (Sep 1, 2011)

> > Your issue if you are describing it right does in fact sound like an electrical issue. Does it do it every time you go out? You can use the timing light as pointed out above to determine if you have a spark issue keep a close eye on the light it may not just quit firing but start missing. You can not check the entire firing systems with out some special tools. But you can check some, I think I remember you saying you had a manual in it will be the procedures to check the components you can. Let me know if you need any help.
> >
> >
> > Standing by
> ...


Let me know if you need any help, I might even be down in the lagoon area next week, might be able to meet up with you help diga. 

Standing by


----------



## Dillusion (May 21, 2012)

> > > Your issue if you are describing it right does in fact sound like an electrical issue. Does it do it every time you go out? You can use the timing light as pointed out above to determine if you have a spark issue keep a close eye on the light it may not just quit firing but start missing. You can not check the entire firing systems with out some special tools. But you can check some, I think I remember you saying you had a manual in it will be the procedures to check the components you can. Let me know if you need any help.
> > >
> > >
> > > Standing by
> ...


If you will be here, let me know I will meet you.

The manual calls for a harness adaptor to test the CDI and coil output, but I'm pretty sure I can accomplish the same with with carefully placed paper clips and my DMM.

I will be re-doing compression and spark test while the outboard is 'hot' tonight or tommorow, will post back.


----------



## HaMm3r (Dec 11, 2006)

> > > > Any chance it's ventilation of the prop that's causing the RPM fluctuations? Perhaps if you're running the prop close to the surface it's ventilating a bit, then all of a sudden it gets a little more bite and RPMs drop until it begins to slip again. That would explain why it does it less at WOT, since you'd be running higher on plane, thereby farther above the slip/grab water level.
> > > >
> > > > No idea how your motor is mounted, but if you can trim it down farther and test again, it might save you some headache.
> > >
> ...


That's it, but more specifically "slipping a little more than normal all the time". As I'm sure you know, just because a prop isn't completely blowing out doesn't mean it's not ventilating. There's a point on mine about mid-throttle and trimmed just right (or wrong in this case) where the the prop will alternate between slipping and grabbing over and over as the boat gains and loses speed slightly. 

Everyone else seems convinced it's electrical, and it may very well be, but if that doesn't pan out, just keep the prop possibility in mind.


----------



## Creek Runner (Sep 1, 2011)

> > > > > Any chance it's ventilation of the prop that's causing the RPM fluctuations? Perhaps if you're running the prop close to the surface it's ventilating a bit, then all of a sudden it gets a little more bite and RPMs drop until it begins to slip again. That would explain why it does it less at WOT, since you'd be running higher on plane, thereby farther above the slip/grab water level.
> > > > >
> > > > > No idea how your motor is mounted, but if you can trim it down farther and test again, it might save you some headache.
> > > >
> ...


You are correct in your thinking, the only thing is if your use to running boats and hearing engines run. There is a significant difference in dropping rpm's due to an electrical issue and ventilating prop (rpm's up or down). I'm going off Matty's mechanical experience and operation of boats to know how a prop sounds when it's ventilating. What he described the way he describes it doesn't lead me to believe it's prop related. But then again if a customer came to my shop and said it was doing X my 1st thing would be to duplicate the problem on the water. That way I would know where to go ie electrical, fuel, prop etc 

Standing by
Creek


----------



## cutrunner (Jun 8, 2010)

> > > > Your issue if you are describing it right does in fact sound like an electrical issue. Does it do it every time you go out? You can use the timing light as pointed out above to determine if you have a spark issue keep a close eye on the light it may not just quit firing but start missing. You can not check the entire firing systems with out some special tools. But you can check some, I think I remember you saying you had a manual in it will be the procedures to check the components you can. Let me know if you need any help.
> > > >
> > > >
> > > > Standing by
> ...


Negative Matty.
You will need a peak voltage adapter, it does a lot more than be a fancy paperclip


----------



## Dillusion (May 21, 2012)

> > > > > Your issue if you are describing it right does in fact sound like an electrical issue. Does it do it every time you go out? You can use the timing light as pointed out above to determine if you have a spark issue keep a close eye on the light it may not just quit firing but start missing. You can not check the entire firing systems with out some special tools. But you can check some, I think I remember you saying you had a manual in it will be the procedures to check the components you can. Let me know if you need any help.
> > > > >
> > > > >
> > > > > Standing by
> ...


I don't have a PVA/DVA I only have. Regular DMM


----------



## cutrunner (Jun 8, 2010)

You cant really test a whole lot with just a dmm. You can ohm out a few things. Check your plugwires
Simple enough. You can always start at the sparkplug and check your way back down the system
Have you tried new plugs?


----------



## Dillusion (May 21, 2012)

> You cant really test a whole lot with just a dmm. You can ohm out a few things. Check your plugwires
> Simple enough. You can always start at the sparkplug and check your way back down the system
> Have you tried new plugs?


The plugs are brand new...maybe six weeks old.


----------



## Dillusion (May 21, 2012)

I ran the engine in idle and also revved it up a few times to 1500RPM to heat it up. i then tested...

Compression is 100psi on all cylinders.

Spark tester shows no signs of stopping or else at idle speeds.

Motor is not overheating and is 114-120 degrees on the outside of the block with my laser thermo.

My spark plugs looked pretty dirty for being 'new' but they are not fouled or gunked up just very black. The gaps were still ok and were all 1.00 on all three sparks.

My carbs are all 1.5 turns out from lightly seated on the air/fuel mixture screws in the top corner...

I have a new lower-cowling QD socket coming just incase it's taking in air somehow, will also get the prop cupped this weekend or next week to test that.

When I pump my primer bulb after not running the engine for a few days to get it primed, I can hear the fuel running through the system like it emptied allot...and I can hear a hissing sound as it's being filled back up until the ball is tight.

I had the cowling off while testing this, so I'm assuming the internals didnt get anywhere near as hot as they do on a 95 degree day in the sun with the motor running WOT...the CDI was cool to the touch.

The service manual states 'if there is spark' the CDI cannot be bad, I dont know how true that is as something can be expanding inside with heat.

I just dont want to play 'replace random parts' especially when the CDI pack is $450 online... :'(..stator is $100-200...etc


----------



## HaMm3r (Dec 11, 2006)

> The service manual states 'if there is spark' the CDI cannot be bad, I dont know how true that is as something can be expanding inside with heat.


That is definitely wrong. I had a bad control box that would only allow the motor to just barely run at idle when fully choked. The warranty replacement solved the issue with no other adjustments.


----------



## topnative2 (Feb 22, 2009)

I had similar problemon 2 diff. motors w/ 2 diff. causes .

1. fuel starvation due to h2o seperator filling w/ h2o and not allowing enough fuel to get to motor

2. the glue holding the magnets under the fly wheel would heat up and allow them to move which killed the timing---it was not discovered till the motor was stopped immediately when it occured and the fly wheel removed


----------



## Dillusion (May 21, 2012)

I ran the skiff today at WOT for 20 minutes straight and the problem disappeared. There's no way it's a heat issue with the electronics.

Is there something on the stator that's non heat related?


----------



## cutrunner (Jun 8, 2010)

It fixed itself!!!! [smiley=1-dancingchief.gif] [smiley=deadhorse.gif] [smiley=dancing3.gif] [smiley=bravo.gif] [smiley=jackson.gif] [smiley=partyguy.gif] [smiley=violent1.gif] [smiley=woot.gif] [smiley=thumbsup.gif]


----------



## HaMm3r (Dec 11, 2006)

It disappeared after 20 minutes or it never occurred? Not sure which you meant. :-?

If it never occurred, I'm going to ask if anything was different about weight distribution this trip? Full/empty gas tank? Cooler in another spot? Passenger? Did you add or relocate anything heavy?


----------



## Dillusion (May 21, 2012)

> It disappeared after 20 minutes or it never occurred? Not sure which you meant. :-?
> 
> If it never occurred, I'm going to ask if anything was different about weight distribution this trip? Full/empty gas tank? Cooler in another spot? Passenger? Did you add or relocate anything heavy?


The problem never occurred at WOT from what I can remember. Only when I am at 4400-4900RPM

Nothing was different weight-wise except I had a 170lb passenger instead of the normal 120lb passenger and he was sitting in the middle in front of the console.


----------



## HaMm3r (Dec 11, 2006)

Interesting...50 lbs heavier and the symptoms changed. Just saying...


----------

