2 Stroke 15 HP Johnson Starts Cold But Not Warmed Up

[bigbassin']

As the title states my 2 stroke 15 hp Johnson starts right up and runs great. Once I shut it off and try to get it going again, it really struggles. It may take up to 10 minutes before it will fire again.

My initial thought was over heating, but it pees strong and the cowling doesn’t feel unreasonably warm.

 

Next thing I considered was the engine was flooding, I don’t smell fuel though.

Currently I’m thinking the engine isn’t getting enough fuel, but only if it’s warmed up. The first time I prime the fuel line the ball will firm up, however after it’s been used no amount of squeezing will cause the ball to build pressure. There’s also almost a sucking type sound coming from the engine when I squeeze the ball. Fuel line and injector are both about 2 months old.

Any ideas what may be causing this? I’m not sure why I can build pressure in the fuel line when the engine is cold but not after it’s been warmed up.

[MickD]

 Sounds like you may have a fuel hose check valve issue, but not sure how engine temp could affect that.

 

Maybe two problems?  Insufficient fuel and:  

 

I had a 15 Johnson once which failed an electrical device, had to change a harness.  Not sure of any more detail, but sometimes electrical devices like condensers and coils can go open with temperature changes.  Make sure you have a spark when cranking war

[Way2slow]

First determine if it's fuel.  After pulling it a couple of times, pull the spark plugs out and see if they are wet or dry.  If wet, then it's either getting too much gas and wet fouling the plugs or a lack of ignition or compression.  

If they are dry, it's not getting gas so put a little of premixed in a spray bottle and give a couple of squirts in the carburetor and see if it starts up easily then.  If so, you have a fuel delivery problem.  You can use ether, but I prefer premixed.  

When you post the results of those checks, come back with the results and we can guide you a little further into it. 

 

One thing you can do while you have the plugs out, stick the plug wire on them and while holding the base against bare metal on the motor, try starting it and make sure you are getting a good blue spark on each one.  Make sure you have it firmly against the bare metal of you are going to come back and accuse me of tricking you, because it can light your eyeballs up.

 

 

[king fisher]

The confusing part of your problem is it starts when cold but not when hot.  

If the problem was not getting enough fuel, than the problem would be reversed, not starting cold but ok when warm.  Cold starts require more fuel, reason for the invention of chokes, and primers.

      I would suspect either over heating or flooding.  Seeing ample amount of water coming out the tell tail, (peeing) only means the water pump is working well.  It doesn't mean the water is circulating through the motor correctly.  When did the problem start?  If it started having problems, after running through weeds, or mud, than it may simply be a stuck thermostat. Is the pee water hot?  It should be slightly warmer than the water temperature.  If it is hot than you have a cooling problem.  Remove the thermostat, and see if that solves the problem.  If it does, buy a new thermostat.

    Problems with fuel flooding can be more difficult to fix and can be a result of an electrical issue, or most likely a carburetor problem.  Have you had any water or other contaminant in your fuel?  Have you used gas that was stored for a long period of time?  Have you used oxygenated fuel?  You may only need to start the engine cold, burn a new tank of gas and the problem will fix itself.

       Oxygenated fuel sold at most gas stations, can make O rings, and gaskets swell causing intermittent problems that only show up at certain times, while working fine at times, making diagnosis difficult.  I had this problem with an aircraft once.  After having three engine failures in a 6th month period, I broke down and purchased a new carburetor designed to burn automobile gas. 

       As others have suggested pulling the plugs and checking condition, of the plugs, as well as seeing if they are wet or dry is always the first thing to look at if you can't get an outboard to start.  If you are having a electrical problem, than you may be getting strong spark when cold, but after the motor gets warm the coil doesn't produce enough spark, but if this were the problem, the motor most likely would start to run rough, or quit while running not just problem starts.  Modern motors can have computer boxes, that can be temp. sensitive, which I know very little about.  I can only recommend trying a replacement box if nothing else works. 

      If you have a slightly plugged thermostat, the motor may not be getting to hot to run, but once you shut it off it is too hot to start.

      I owned a 15 horse Johnson two stroke I used for duck hunting.  I was constantly driving through the weeds, causing me to have to clean the thermostat often.  I experienced the same problem you are describing many times.  Only difference was I was hunting in cold weather, and it only would take a couple minuets for the motor to cool down and start.

 

\

[bigbassin']

6 hours ago, Way2slow said:

First determine if it's fuel.  After pulling it a couple of times, pull the spark plugs out and see if they are wet or dry.  If wet, then it's either getting too much gas and wet fouling the plugs or a lack of ignition or compression.  

If they are dry, it's not getting gas so put a little of premixed in a spray bottle and give a couple of squirts in the carburetor and see if it starts up easily then.  If so, you have a fuel delivery problem.  You can use ether, but I prefer premixed.  

When you post the results of those checks, come back with the results and we can guide you a little further into it. 

 

One thing you can do while you have the plugs out, stick the plug wire on them and while holding the base against bare metal on the motor, try starting it and make sure you are getting a good blue spark on each one.  Make sure you have it firmly against the bare metal of you are going to come back and accuse me of tricking you, because it can light your eyeballs up.

 

 

I’ll be sure to try these out next time I have a chance and will post the results.

 

4 hours ago, king fisher said:

The confusing part of your problem is it starts when cold but not when hot.  

If the problem was not getting enough fuel, than the problem would be reversed, not starting cold but ok when warm.  Cold starts require more fuel, reason for the invention of chokes, and primers.

      I would suspect either over heating or flooding.  Seeing ample amount of water coming out the tell tail, (peeing) only means the water pump is working well.  It doesn't mean the water is circulating through the motor correctly.  When did the problem start?  If it started having problems, after running through weeds, or mud, than it may simply be a stuck thermostat. Is the pee water hot?  It should be slightly warmer than the water temperature.  If it is hot than you have a cooling problem.  Remove the thermostat, and see if that solves the problem.  If it does, buy a new thermostat.

    Problems with fuel flooding can be more difficult to fix and can be a result of an electrical issue, or most likely a carburetor problem.  Have you had any water or other contaminant in your fuel?  Have you used gas that was stored for a long period of time?  Have you used oxygenated fuel?  You may only need to start the engine cold, burn a new tank of gas and the problem will fix itself.

       Oxygenated fuel sold at most gas stations, can make O rings, and gaskets swell causing intermittent problems that only show up at certain times, while working fine at times, making diagnosis difficult.  I had this problem with an aircraft once.  After having three engine failures in a 6th month period, I broke down and purchased a new carburetor designed to burn automobile gas. 

       As others have suggested pulling the plugs and checking condition, of the plugs, as well as seeing if they are wet or dry is always the first thing to look at if you can't get an outboard to start.  If you are having a electrical problem, than you may be getting strong spark when cold, but after the motor gets warm the coil doesn't produce enough spark, but if this were the problem, the motor most likely would start to run rough, or quit while running not just problem starts.  Modern motors can have computer boxes, that can be temp. sensitive, which I know very little about.  I can only recommend trying a replacement box if nothing else works. 

      If you have a slightly plugged thermostat, the motor may not be getting to hot to run, but once you shut it off it is too hot to start.

      I owned a 15 horse Johnson two stroke I used for duck hunting.  I was constantly driving through the weeds, causing me to have to clean the thermostat often.  I experienced the same problem you are describing many times.  Only difference was I was hunting in cold weather, and it only would take a couple minuets for the motor to cool down and start.

 

\

Current tank of gas came from a can about 9 months old, would that be old enough to do? Most of this tank has been used for duck scouting so it’s definitely ran to into some mud. 

[MickD]

Get back to what it takes to start an engine.  Do you have a spark?

[slonezp]

Maybe a vent issue with the fuel tank?

[Way2slow]

My first thought is bad compression.

Also, gas can go bad in a couple of months.  Eight month old gas is only good for starting fires or pouring on fire ant mounds.

[MN Fisher]

2 minutes ago, Way2slow said:

My first thought is bad compression.

Also, gas can go bad in a couple of months.  Eight month old gas is only good for starting fires or pouring on fire ant mounds.

Ya - even with Stabil, I wouldn't use any gas more than 6 months old. If it's oxygenated (with ethanol in it)...reduce that by half

[K1500]

Vapor lock?

[Elkins45]

My Lawn Boy two stroke mower would start cold but not restart when hot. The problem turned out to be the ignition coil. Once I replaced it everything was fine.

[TnRiver46]

12 hours ago, Way2slow said:

First determine if it's fuel.  After pulling it a couple of times, pull the spark plugs out and see if they are wet or dry.  If wet, then it's either getting too much gas and wet fouling the plugs or a lack of ignition or compression.  

If they are dry, it's not getting gas so put a little of premixed in a spray bottle and give a couple of squirts in the carburetor and see if it starts up easily then.  If so, you have a fuel delivery problem.  You can use ether, but I prefer premixed.  

When you post the results of those checks, come back with the results and we can guide you a little further into it. 

 

One thing you can do while you have the plugs out, stick the plug wire on them and while holding the base against bare metal on the motor, try starting it and make sure you are getting a good blue spark on each one.  Make sure you have it firmly against the bare metal of you are going to come back and accuse me of tricking you, because it can light your eyeballs up.

 

 

Haha! light you’re eyeballs up. That reminds me…….

 

My grandpa was working on a tiller once when I was a kid. The details are a little fuzzy in my memory but he wanted to see if it was getting spark. After a while he just grabbed the plug and told me to pull the cord. I said “are you sure papaw?” And he nodded. The next thing I know, sweet ole papaw said quite the string of expletives, might have been the first time I heard him cuss. Me and my brother were trying hard not to laugh but we failed 

[MickD]

9 hours ago, slonezp said:

Maybe a vent issue with the fuel tank?

Could be, easy peasy to check, but if a vent is not open the engine will usually in time stall out and not restart. He did not mention stalling, just a failure to restart when warmed up.  

 

I still think the first  (and easy) step is to determine if there is spark when not restarting.  If there is a spark then most likely it is a fuel problem.

[Way2slow]

There are several possibilities, that's why you go through a basic trouble shooting routine and the process of elimination.  For an IC engine to run it takes air, fuel, compression, and ignition at the right time.  All you have to do is go through the process of determining which of those are missing.  Of course, if it's a diesel, you don't have an external ignition but then compression becomes ever more critical.

I have had numbers of engines that would start fine cold and not start when warm.  95% of the time it's either the compression or the ignition.  A cold engine will generally have a lot more compression than a warm engine.  Warm air is thinner and harder to compress than cold air, plus the internal gaps open up on a warm engine.  I don't know how many engines I've rebuilt for this same problem.  The other is the ignition, bunches of times I've had coils and power packs the broke down after they warm. and I've had them to be just the opposite. 

If it's an older motor with points, you will want to check those for pitting and proper gap.

Also note, this is why you always to a compression test on a warmed engine and not a cold engine.  Cold engines compression will lie to you big time.

[thomas15]

Another possibility is an air leak, even a little one will be a big problem. You might not even see gasoline dripping from the fuel lines.

 

If it were me I would get carb rebuild kits and clean-replace all the parts. Examine the carb floats very carefully and if there is any fuel in them replace. Make sure the float level is set properly. Drain and really clean the fuel tank also there very well could be debris gumming up the works.

 

Both a fuel line leak or float needle valve not seating (for whatever reason) can cause the condition of not being able to pump up the system after running the motor. A lack of good spark is not causing that problem but it could be contributing to a lack of performance. I assume this motor has two carbs, they need to be in syncro and idle mixture is properly set. The OMC shop manual for your exact motor will give you the sequence to check everything, worth getting if available. 

 

I have in the 8 years I have had my boat acquired the shop manual, float measuring tool, spark gap testers (3 of them), I already had a strobe timing light, I stock two full sets of carb rebuild kits, two sets of carb gasket kits, water pumps, spark plugs, extra fuel pump, lines, filters and clamps and more! No spring is complete without having to tear into my outboard to find out what's not working. Everything I know about 2 strokes I have learned in the time since buying my boat.

 

While I have used regular 87 octane fuel, plus 89 works way better for me. I put Sea Foam in the tank every time I buy gas. Make sure your fuel lines and hoses are all rated for ethanol use. As others have said 6 months shelf life is it once I get to that point I put the fuel into my car and buy new.

 

None of my two strokes are anywhere as picky as my Merc 50 outboard. My chain saws, leaf blower or weed wacker can sit for 6-8 months or more and start right up. My boat can sit for two weeks and then kick my butt. When it runs, it runs fantastic. When it doesn't it makes me want to sell it then take up playing chess.

[bigbassin']

Looks like the fuel may have been the issue. 
 

Pretty much ran out the last tank and filled back up with new non-ethanol gas, so far so good this morning.

[WRB]

You had expert advice offered. Starts easy cold may be because you prime the fuel to the carb and choke it to get started, indicating the spark plugs are working OK to me.

The simplest fuel supply problem and most common is your prime bulb is defective reducing the fuel supply. The second most common problem has been discussed and that is the thermostat isn’t opening to allow cooling water after the engine has warmed up enough to open it.

Both easy things to check before diving into more complicated fixes.

Tom