15 HP with no power and low rpms

[scout-j-m]

Coils came in Saturday and I installed them along with the new plug wires the same day. Set the gap on the new plugs Sunday and installed them, along with a new inductive tach. Then took it to the lake to test. Not much improvement. Motor only topped out at 3100 rpms and 7 mph on my 1648 flatbottom. I verified the throttle plate was opening all the way, that fuel was flowing through the clear fuel line into the carb, and tried pumping the bulb. Cooling water was pumping good and the engine block was nice and warm but not hot. I brought some Deafoam Deep Creep spray and gave it some mild squirts at WOT but rpms didn't increase any. Gave it some longer shots to where it bogged even more and smoked a lot but rpms only came back up to 3100 after it burnt it off.

I didn't do a spark check since putting on the new coils but I have a feeling that will check out. I'll do that and another compression check for kicks but I'm stumped yet again. Doesn't really seem like an ignition system issue as there is no noticeable misfire but I guess the high speed side of the charge coild could be bad? I'll post some pics of the plugs when I pull them this evening to see what yall think, if anything, after looking at them. Last time I pulled them they appeared very wet with fuel and with no signs of water. Should I pull the exhaust port and check that out? Just needs some ideas on what to try next.

 

[oldboat1]

hull weight, weight distribution and propping?

 

[scout-j-m]

hull weight, weight distribution and propping?

Prop is the standard 10" one these motors come with. Is a pretty beat up one as one blade's leading edge has mushroomed some but I have seen worse. I do have another in better shape I need to put on though.

Hull weight is pretty low. Hull is 300 lb, I'm 170, has a 12v bow mount trolling motor, group 29 deep cycle battery, ~3 gal of gas, front seat pedestal/seat, and 50 lb rubber mat floor plus a few rod/reels and tackle box. The only shiftable weight is the battery but it makes no noticeable difference if it is in the bow or stern. The hull is rated for a 35hp motor, 4 people/600 lb, or 1000lb people/motor/gear. I'm well below that and it is literally drafting inches of water.

For comparisons sake I have a 1967 9.5 hp Sportwin with just 65 psi in each cylinder and a like new Solas prop in the standard size and that motor with the same load pushed the boat 15 mph at 4800 rpms (4000-5000 factory rec range I believe). The Sportwin also created more drag as the anti-vent plate is slightly lower and it's old design lacks the second plate above it to help divert water down and away from the wider part of the exhaust leg. I'm not sure it's an apples to apples comparison but I would think a 15 hp with good compression would match that performance and then some.

I just trimmed down the water tube on my same model year 9.9hp in order to make it a short shaft but have yet to try it. It runs much smoother in a barrel than the 15hp but like I mentioned I have never had it in the water. If it pushes the boat well it will be the perfect baseline to go against. With my current luck, however, it will likely have major issues as well....

 

[Tim Frank]

I'm guessing, because there is a`lot of info missing.
But:
1) it does not sound like it ever has run properly for you
2) I'd be looking at fuel issues....carb issues.

Did you just "clean" the carb, or did you do a proper o/haul?
R&R and clean the high speed orifice, AND MORE IMPORTANT, VERIFY THAT IT IS THE CORRECT ONE"

I've run into many instances where previous owners decided that they were smarter than the OMC engineers and did some "creative re-design".
They rejet....or use a "equivalent carb....or whatever.
Just because your motor came with a carb installed, DO NOT assume that it is OEM configuration.

An undersize carb will do this.

 

[scout-j-m]

I'm guessing, because there is a`lot of info missing.
But:
1) it does not sound like it ever has run properly for you
2) I'd be looking at fuel issues....carb issues.

Did you just "clean" the carb, or did you do a proper o/haul?
R&R and clean the high speed orifice, AND MORE IMPORTANT, VERIFY THAT IT IS THE CORRECT ONE"

I've run into many instances where previous owners decided that they were smarter than the OMC engineers and did some "creative re-design".
They rejet....or use a "equivalent carb....or whatever.
Just because your motor came with a carb installed, DO NOT assume that it is OEM configuration.

An undersize carb will do this.

1) Short answer is no. I bought the motor based off it being ran in a barrel and having good compression. After I bought it I replaced the fuel lines, checked the impeller (since PO said it had a new one, which it did), and checked for a 1/2" spark. Tried it out once on a 1436 and it had a good burst of power on the initial throttle (better than the Sportwin which I had also just tested) then bogged down to what I am doing now. That's when I decided to rebuild the carb, which was free of varnish and just had a little rust on the float bowl which I removed with a wire brush.

2) I did a full rebuild/cleaning of the carb. I removed the welched plugs, removed the main stuff with carb cleaner, then soaked it in ChemDip. Then cleaned with water followed by compressed air and more carb cleaner. I put in new welch plugs, float, needle, needle clip, seat, seat gasket, low speed bushing, and float bowl gasket. Cleaned the high speed jet but did not check it to verify it was the correct one. Also didn't verify the carb part number to the parts diagram, however, the carb throat is definitely larger than my 9.9's one.

I can go back and check the carb to try to verify it is the correct one and that the jet is correct also. this does make me wonder why it had that initial "burst" on my forst test on the 1436 but then regressed to what it is now. Someone else suggested that their may be blockage in the exhaust. Like as in it had some kind of massive carbon build up that broke off from in the exhaust port and is restricting it? Seems like a longshot but I guess anything is possible. I'll check the carb, do another compression test, check spark once more with the new coils, and post some pics of the plugs.

 

[oldboat1]

It sounds like you are a careful guy. In keeping with Tim Frank's thought, I was going to suggest comparing carb throat size to a 9.9, but you are on to that comparison. It's possible that it's got the wrong h.s. jet, I guess -- although probably more likely for a 9.9. (Unless somebody tried to juice up a 15 into a 20 or 25, maybe. I'm not sure what performance issues over jetting would give you -- guess there would be stumbling.)

That idea about an exhaust blockage might have some merit, although it doesn't have to be carbon blockage in one of the exhaust ports. You could have remnants of a critter's nest somewhere (prop area, up in the leg, etc.) Been there.

Any chance that your oil/gas mix is too rich? Maybe contaminated gas in a built-in tank?

 

[Tim Frank]

Here is a good case study http://forums.iboats.com/forum/engi...ds/615948-9-9-evinrude-won-t-go-over-3000-rpm

 

[OptsyEagle]

On the exhaust theory, have you tried running it WOT without the hood on. Sometimes if you get an exhaust leak it will bog down or even die at higher speeds, but when the hood is removed it gets the air it wants and takes off. It doesn't confirm an exhaust blockage but is an easy test to see about an exhaust leak (which can also happen during an exhaust blockage).

 

[scout-j-m]

Here is a good case study http://forums.iboats.com/forum/engi...ds/615948-9-9-evinrude-won-t-go-over-3000-rpm

Thanks. Seems to have similar symptoms as me. Didn't have a chance to do any troubleshooting last night due to the weather but hopefully can get back on it tonight.

 

[scout-j-m]

On the exhaust theory, have you tried running it WOT without the hood on. Sometimes if you get an exhaust leak it will bog down or even die at higher speeds, but when the hood is removed it gets the air it wants and takes off. It doesn't confirm an exhaust blockage but is an easy test to see about an exhaust leak (which can also happen during an exhaust blockage).

Yeah, most all of my testing has been with the cowl off. But have also tried it enough with the cowl on to know it runs the same that way too. At least that's one problem I don't have to worry about.

 

[lmuss53]

If you have a good running 9.9 stick that carb on and see if the 15 runs good with it too. That could provide a wealth of information for about 30 minutes of labor.

Before you do that pull the fuel pump off the 9.9 and try the 15 with that. I know you've pumped the ball, but I have seen fuel pumps fix similar problems on OMC small twins even when pumping the ball didn't change asnything.

 

[scout-j-m]

If you have a good running 9.9 stick that carb on and see if the 15 runs good with it too. That could provide a wealth of information for about 30 minutes of labor.

Before you do that pull the fuel pump off the 9.9 and try the 15 with that. I know you've pumped the ball, but I have seen fuel pumps fix similar problems on OMC small twins even when pumping the ball didn't change asnything.

Ok, I can try that.

 

[scout-j-m]

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.

 

[scout-j-m]

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.

 

[scout-j-m]

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?

 

[oldboat1]

looks pretty normal to me -- some rich running (water fuel mix giving you some goo). Running cold or in a barrel/on muffs can give you that too. Wouldn't hurt to just clean it up some. Grab a flashlight and check up the exhaust to see if you can spot anything up there (wasp nest or similar). Probe a little if it looks like something is up there.

 

[scout-j-m]

looks pretty normal to me -- some rich running (water fuel mix giving you some goo). Running cold or in a barrel/on muffs can give you that too. Wouldn't hurt to just clean it up some. Grab a flashlight and check up the exhaust to see if you can spot anything up there (wasp nest or similar). Probe a little if it looks like something is up there.

Will do. Thanks for verifying it all looks normal.

 

[lmuss53]

That is un burbed fuel. Check the float height, It might be a little high, letting too much fuel in, choking out the engine but not running out the throttle body.

Your comment that it runs better for a minute right after you start it suggests that to me.

 

[scout-j-m]

I 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.

 

[scout-j-m]

I just returned from vacation, but prior to leaving I ran the 9.9 hp again but popped in the new plugs I had in the 15 hp. On the water I burned through a can of Seafoam deep creep at WOT to do somewhat of a decarb. With the new plugs and decarb, the 9.9 was now doing 5400 rpms and just shy of 17 mph with just me in the boat. I feel like it is running pretty good now aside from not wanting to idle down consistently as low as it should.

So next, I plan on putting the 15 hp carb onto the 9.9 and giving it a run. If it runs up to WOT plus some extra rpms due to the increase in fuel/air then I can confirm the 15 hp carb is good. At that point I will leave the 15 hp carb on the 9.9 and swap the fuel pumps. If I rule that out, I will then investigate why I lost spark as it would be the likely culprit at that point I guess.