15 HP Evinrude help - No power or rpms

[wmk0002]

Ordered some OEM coil kits that come with new plug wires just a little while ago. Hopefully get them in and installed early next week. I'll post an update on everything then. Thanks for the help guys.

 

[RiverLife]

I would be checking the exhaust ports first before ordering any parts. If they are built up with carbon it wont rev up or have any power.

Good job on the carb rebuild and compression check. Now you have a good baseline down. I would also change the plugs and make sure gap is correct. How about fuel filter?

Coils work or they don't generally or may cut out when engine gets hot. You described more of a bogging rather than miss firing. I feel coils are ok.

You can try starting engine in the dark to see if wires are arching out. Bad wires will also be a misfire and not a bogging condition.

My guts tell me to check exhaust on this one.

Color of spark plugs tell a story. What color are they?

 

[wmk0002]

Well.... coils came in amazingly fast getting here Saturday. Ordered them from MarineEngine.com btw. So Saturday I installed the new coils, plug wires, and plugs(gapped to 0.030"). Then Sunday took it to a small local lake for a test run and had no real noticeable improvement. I installed a new inductive tach and using my phone's gps was seeing max speed of 7 mph at max rpms of 3100. While out I verified that the butterfly was fully opening, that fuel was flowing through my clear fuel line between the pump and carb, and that it was pumping good water and cooling. I brought a can of the the Seafoam Deep Creep and gave it a few quick squirts to see if it responded like it was starved for fuel but it didn't help. Then I gave it some longer blasts like you would do for a decarb for kicks and it bogged worse and smoked a ton but then came back up to the same rpms as before.

I'm going to revisit my spark and compression test again along with pull the flywheel to check the ignition components under it and to check the shear key. I'm not sure what ignition problem would contribute to this now. I know the charge coil under the flywheel typically has a high speed and low speed output so maybe its possible the high speed side is bad but I can rev the motor up much higher in neutral in a barrel with out any cutting out. Maybe the spark can keep up but gets weaker at that speed?

But Rivelife may be on to something. At this point, if there was a serious ignition problem I think I would be seeing some different symptoms. This motor does have some nasty goo coming out of the exhaust leg and thru hub exhaust ports when I run it on muffs or in a barrel. Stuff looks like light gray grease. Can I pull the exhaust port cover and inspect or will I need to totally pull the powerhead?

 

[wmk0002]

To address a couple other points Riverlife mentioned, I have not messed with the fuel pump or it's filter. I have totally forgot the fact that the fuel pump diaphragm could be leaking and flooding one cylinder. I will check that.

As to color of the plugs, both are very wet with fuel. No water that I can tell. Seems like more fuel is being delivered than can be burnt.

I'll pull the plugs this evening and post pics. Also post some better pictures of my old coils. Even if they were still good, I'm glad I changed them because they looked rough.

 

[RiverLife]

Man I have worked on more motors than I care to admit.

By what your telling me now it's time for a new carb. I have pulled my hair our with similar problems recently with a 15hp Mercury. I would run it in a barrel and it would muck up the water and pump fuel out the exhaust. Plugs were soaked. I rebuild carb and fuel pump and it was worse.

Sometimes carbs won't atomize fuel any longer and need replaced. The Merc 15 starts on one pull idles nice and runs good now with new carb.

Make sure lower unit does not have any fishing line around it and that it spins free and lube is good.

Have confidence in yourself and you will figure it out. Keep at it and keep us posted.

 

[wmk0002]

Man I have worked on more motors than I care to admit.

By what your telling me now it's time for a new carb. I have pulled my hair our with similar problems recently with a 15hp Mercury. I would run it in a barrel and it would muck up the water and pump fuel out the exhaust. Plugs were soaked. I rebuild carb and fuel pump and it was worse.

Sometimes carbs won't atomize fuel any longer and need replaced. The Merc 15 starts on one pull idles nice and runs good now with new carb.

Make sure lower unit does not have any fishing line around it and that it spins free and lube is good.

Have confidence in yourself and you will figure it out. Keep at it and keep us posted.

I'll look into it. I didn't know a carb could really go bad though. I have a 9.9hp of the same year I just made some progress on but have yet to try out. If it performs well I can do a carb swap between the two and see what happens on each.

 

[kofkorn]

Pull the carb and look at the float. Not sure when the change happened, but they went from a cork float to a plastic one. The old cork floats can sometimes get "Waterlogged' and will sit lower in the fuel than they should. It causes the fuel level to run higher than it should and can cause a rich condition at open throttle. You don't usually notice it at idle because you adjust for it with the low speed needle. I bought a motor that had this condition. It would run poorly and occasionally stall at WOT. I changed out the float and it ran like new.

Every time I open an carb and see the cork floats, I replace them with a new plastic one. It's not worth the chance.

Good luck!

 

[perchjerker]

even though the coil did not fix it you did the right thing to replace them

 

[wmk0002]

Pull the carb and look at the float. Not sure when the change happened, but they went from a cork float to a plastic one. The old cork floats can sometimes get "Waterlogged' and will sit lower in the fuel than they should. It causes the fuel level to run higher than it should and can cause a rich condition at open throttle. You don't usually notice it at idle because you adjust for it with the low speed needle. I bought a motor that had this condition. It would run poorly and occasionally stall at WOT. I changed out the float and it ran like new.

Every time I open an carb and see the cork floats, I replace them with a new plastic one. It's not worth the chance.

Good luck!

I replaced the old float with the new one that came in the OEM carb kit. I adjusted it to level when turned upside and blew through the fuel inlet with everything I had but couldn't get it to blow through. So I'm pretty sure my float and its setting is good. I also have new fuel hose so I should be debris free withing the fuel system. Probably need to add a filter to the fuel tank hose and check the screen on the fuel pump though.

I'm glad I changed the coils too. If I end up just using my 9.9 hp, I will swap coils so the one I'm running has the most up to date ones so it definitely wont be waste.

 

[wmk0002]

Copy and pasted below is my post from the iboats forum. The high speed jet test was done per a rec on there.
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Here is what I did last night. I removed the carb to check out the high speed jet. It was really hard to read but I'm almost certain it said "58 15". My guess is that means it is a 0.058" size jet for a 15 hp? When I tried researching what 15 hp took that size of jet I got a hit for a 2000 model 15hp. Based on my searching through the parts diagram for my motor, I should have a size 56 jet. Aside from the jet, I checked the entire carb out again. It was really clean, full of fuel, and the vent was clear. The needle valve was seating fully when I inverted the carb and it wasn't sticking. I put it all back together and moved on to some more tests.

Next I pulled the plugs. The top cylinder's one was pretty clean and the bottom's was dirty. With the Seafoam Deep Creep I was spraying in it on my last water test I would think both would be really clean if the spark was as it should be. So then I did another spark test and both plug leads were jumping a half inch gap like before. I then put the plugs back in and ran the motor while attempting to use my multimeter to measure the voltage on the leads going to each coil. According to the troubleshooting guide I saw they should both have 150V no mater the rpms, but should increase with rpms up to 300-400V. For whatever reason my multimeter wasn't working but in probing the wires the voltage was arcing up my test leads and to the block and killing that cylinder. I tried it again closer to the powerpack and this time it died and I also lost all spark. Not really sure what happened...I know it is not a kill switch problem because the black kill wire from the pack is taped off and I kill the motor by just backing the throttle all of the way off.

A note I would like to add is that when I first fired the motor up (cold start) I manually pushed the cam roller to give it some gas and rev it up. When doing this, for the first 10-15 seconds, the motor ran smoother than it typically does and the throttle response was almost immediate like lit should be. But as soon as it warmed up just a little it went back to feeling like it was maybe missing and bogging when I quickly gave it throttle.

 

[wmk0002]

After getting bummed out with my work on the 15hp, I removed the LU from it and installed it on my 9.9 for the first time since cutting the water tube to convert it from long to short shaft. I ran it in a barrel and it ran pretty good. So after work today I think I will take it to the lake for a test run on my boat to see how it performs. If it does ok, I think I will drop in the 15hp carb and give it another test. If that works too, I can basically rule out the carb on the 15hp. I can take it from there and maybe try a powerpack swap, fuel pump swap, etc and maybe narrow it down further that way.

 

[wmk0002]

Also, FWIW, this is what the bottom of the exhaust leg looked like after I pulled the LU. Is the gray, foamy exhaust a sign of anything in particular? Seems like it would be caused by a lot of unburnt oil. Also, why is the main exhaust tube exit so resitricted? It appears there is a larger hole above the two smaller ones that has a piece plugging it up. Is that correct way everything should be?

 

[kofkorn]

The two different spark plugs is concerning. You may have a head gasket leak, letting water into the cylinder with the clean plug. Can you shine your flashlight inside the cylinder and see any water droplets after running a few minutes? If you have one cylinder that is sparkly clean as compared to the other, it is usually an indication of water intrusion.

A gray foamy mix could also mean you're running rich. The gray foam is the emulsified fuel/oil combo that mixes with the water coming out of the exhaust. It's usually an indicator of a carburetor issue. I'd check your float level again. Also make sure that the gasket isn't extruding into the carburetor space. Sometimes if the gasket isn't positioned properly, the float can get hung up on the gasket, preventing it from fully seating.

An easy way to test this is to take your boat out and get it running. Warm it up and get it going as fast as it currently can. Then go back to idle, disconnect the fuel line and immediately go back to WOT. If you have a fuel level issue, the motor will run slow for a few seconds and then as the fuel level in the bowl drops, the motor will gradually speed up to a normal high speed WOT, before eventually stalling from lack of fuel. (Don't try this with a multi-carbed engine, you could starve your top cylinder before the bottom one runs out of fuel)

Hopefully this will eliminate any worries of an electrical issue.

Good luck!

 

[Sinkingfast]

About that exhaust restriction...

When I rebuilt my 76' 15hp I did away with the wet leg and installed the megaphone exhaust. When i did some research..like 2 years on that motor..I saw that the megaphone mids had various versions of that outlet. Some had 3 holes, others 3 holes with one plugged..and with just those 2 holes and no 3rd hole or plug. Even saw one on ebay with a nut and bolt in that large 3rd hole. Ebay is good for more than buying..

 

[wmk0002]

I appreciate all of the help guys!

I do have some good news in that I tested my 9.9 out yesterday evening and it worked really well. I'll shy away from great as it could probably use a tuneup itself but it started easy, idled decent just not down very low, and got up to WOT with no hesitation or misses. It pushed my boat 16 mph at about 5100 rpms with just me in the boat and did 14-15 mph at 4900 rpms with my dad in the boat with me. This was done with a decent shape standard 10" prop. According to the prop calculator I used those rpms and speeds indicate a lot of prop slip (19-25%) but I guess that is expected with a smaller motor and a big boat as it doesn't really seem to get fully on plane so it has extra drag. As a side question, would this motor on this boat be best paired with a 9" prop and would a 4 blade, if available in that small of a size, allow better "grip" which may reduce my prop slip and help my speed/rpms a little?

So now with a running 9.9 motor, now I can start doing some carb swaps. I think I will drop the 15 hp carb on the 9.9 next and give it another try. If it runs well and I see the expected rpm gains then I'll know I can rule it out. If not I can try the advice to disconnect the fuel and see if it picks up rpms as the fuel bowl level begins to lower which would indicate an improper float height. Likewise if the carb seems to be the issue, I can then later put the 9.9 carb on the 15 to see if it performs similarly to the 9.9 or if possibly has other issues.

In addition to the carb, both the fuel pump and powerpack will be easy swaps as well if it comes to that. So I feel I am in a good position now going forward....plus I have a working motor I can use in the meantime which is huge.

 

[wmk0002]

Just got back from from vacation so haven't done any fiddling with the 15 hp recently. But I did take the boat out with the 9.9 hp again the day before I left. This time I took some Seafoam deep creep with me plus installed the newer plugs I had previously put in the 15. This trip out, after running it hard and doing a halfway decarb with the deep creep, I was seeing 5400 rpms by myself and was just shy of 17 mph.

I think I am confident enough now with this motor that I will try the 15 hp carb on it next.

 

[wmk0002]

Put the 15hp carb on the 9.9 hp the other day and ran it in a barrel yesterday. Ran great in the barrel so I plan on giving it a lake test this weekend. I'll post back with results and I'll try to shoot a video as well.

 

[wmk0002]

I was able to take the boat out this morning for some fishing and to try out the 9.9hp with the 15hp carb. It ran almost identical to when the 9.9 carb was on and ran well. I only saw a couple hundred more rpms up to 5600 and maybe 0.5-1 mph gain but it still ran good so I guess that at least proves that the 15hp carb is good and isn't the source of my 15hp lacking power. I forgot to take the 15hp fuel pump with me to try that out but will do that next. I'm making some progress here at least.

And if anyone has any ideas why I didn't see the expected rpm gains from the 15 hp carb I'd like to hear them. I know im missing the reed spacers and tuned exhaust tube to go the full way to the 15 hp but I thought the carb alone would do more. Is it still possible the carb has a minor issue like the jet possibly being the wrong one? In a previous post I mentioned I thought it was a jet from a more modern 15hp carb and was a couple thousandths larger than what it should be. I'm certain the throttle plate was fully opening at WOT too.

 

[perchjerker]

dont dismiss the need of the reed valve spacers and exhaust tube. The motor needs to breathe properly with the different carb so you may not see much difference without them.

I dont have any direct experience with this motor but was an automotive mechanic most of my life and I can tell you to maximize performance of an engine (which is basically an air pump) all the components must be in place for maximum output from the setup

 

[Pappy]

I was able to take the boat out this morning for some fishing and to try out the 9.9hp with the 15hp carb. It ran almost identical to when the 9.9 carb was on and ran well. I only saw a couple hundred more rpms up to 5600 and maybe 0.5-1 mph gain but it still ran good so I guess that at least proves that the 15hp carb is good and isn't the source of my 15hp lacking power. I forgot to take the 15hp fuel pump with me to try that out but will do that next. I'm making some progress here at least.

And if anyone has any ideas why I didn't see the expected rpm gains from the 15 hp carb I'd like to hear them. I know im missing the reed spacers and tuned exhaust tube to go the full way to the 15 hp but I thought the carb alone would do more. Is it still possible the carb has a minor issue like the jet possibly being the wrong one? In a previous post I mentioned I thought it was a jet from a more modern 15hp carb and was a couple thousandths larger than what it should be. I'm certain the throttle plate was fully opening at WOT too.

Perchjerker has nailed it perfectly.
The carb is only part of the upgrade. You have now modified the front end of the "air pump" but cannot properly get the benefit of opening up the intake side without modifying the exhaust to take advantage of it. The side benefit here is that, once you pull the powerhead you can also get new water tube grommets and replace the old and probably restrictive ones and replace all your fuel lines while you are there.