OMC 15hp Running on one cylinder

[2shallow2sail]

Hi All- I am stumped on this one and looking for ideas. My bottom cylinder is not working. Here is the background:

1974 Evinrude 15hp. I purchased used (it was running, not well though). I did the following:

Converted from Long to short shaft
New impeller
New Coils
New Plugs
New T-Stat
Changed LU oil
Gapped points to .020"
Carb Kit/Clean
New fuel pump
Compression is 110psi on both cylinders
New points and Condensers (this was recent in attempt to fix current problem)
Sea foam treatment (this was recent in attempt to fix current problem)

Initially i had trouble with it running on one cylinder, that was fixed when I pulled the flywheel and adjusted the points. Then i had trouble with it flooding and that was fixed when i replaced the rod that holds the float onto the carb. At that point, it was running perfect for a couple weeks at all RPM's and very little to no hesitation when revving up to speed. Then it started to surge at all speeds and hesitate on acceleration. I did the seafoam treatment and changed the plugs and it was running perfect again for a couple of days. Then it started to get worse, a couple of times at high speed it cut back to almost idle speed on its own, but got back up to speed after a minute. Then it became very hard to start and was only running on one cylinder. At that point I did the following:

Compression test: still 110psi on both
Cleaned carb
cleaned plugs
Checked points gap, seemed ok but I fine tuned it.
At that point it was still only running on the top cylinder (it would die if i pulled the top spark wire off, but nothing changed when i pulled the bottom off).

At this point I did the following:
Blew out carb again.
Chaged points and condensers to new.
Still no luck

I have also swapped the plugs and swapped the coils with no change. I am getting a pretty decent blue spark on both cylinders. It does not appear to have water in the lower cylinder but I am not positive. I am thinking my timing is possibly off (I read on Leeroy's Ramblings there is a friction ring on these old motors that can slip). Or maybe i am flooding and the lower cylinder is not firing due to that. I pulled the plug out and pulled started rope, I didn't see a crazy amount of mist come out. I also tried putting fuel directly in the cylinder, i dont think it helped. Any ideas would be much appreciated, i dont know where to go from here.

PS- I am looking to get a motor for my small tender that I take sailing with me. I am between a used 3.5 nissan 2 stroke ($350) and a new suzuki 2.5 4 stroke ($700). I will also use this on my big dink while I am trying to fix the 15hp. Any thoughts? I am pretty familiar with 2 strokes, but not at all with 4 strokes from a maintenance perspective.

 

[Rick.]

Re: OMC 15hp Running on one cylinder

A couple of things come to mind but first I have to say you've done a lot and all good IMO. I have heard if the diaphragm on the fuel pump goes it will leak into the bottom cylinder causing the bottom to flood. The only other thing that I would recommend you check is for a foreign object in your reeds or even a bent or broken reed. Not very likely but it has happened to me (a small piece of plastic broken off the slow speed knob) and my symptoms were very similar to yours. I can imagine how frustrating this is when you've done so much. Best of luck. Rick.

 

[2shallow2sail]

Re: OMC 15hp Running on one cylinder

thanks Rick. The entire fuel pump is only 3 months old so I'd like to avoid taking it apart if possible (for now), those things are tricky. I actually did break a couple pieces off my slow speed knob as well, but that was in the spring and i think I got them all out but i think it is worth looking at. I have never taken off the manifold. The reeds are actually called "leafs" on the diagram correct? I guess i just need the 2 gaskets if i take it off. If the reeds are fouled, would that cause the cylinder to flood? The plug is wet so fuel is getting in there. Any tips on how to tell if water is also getting in there?

http://www.**********/parts/search/BRP/EVINRUDE/1974/15404S/INTAKE MANIFOLD/parts.html

 

[Sureshot]

Re: OMC 15hp Running on one cylinder

I've got a similar problem to yours, runs only on the top #1 cylinder in idle, good spark, good compression. Mine however picks up fine once I get out of idle and the engine runs good in high speeds. I'll be setting some time aside this weekend to go through the #2 carb. My understanding of the problem would be either what Rick suggested, fuel pump leaking back into the bottom carb, or a straight carb issue. Possibly a stuck float that's flooding the cylinder or gunk in the idle circuit that's preventing fuel from getting there. Does your 2nd cylinder pickup past idle?

 

[AlTn]

Re: OMC 15hp Running on one cylinder

is the fuel pump "new"? or did you rebuild the old one?..I ask because the rebuild is "tricky" and may, indeed, be leaking into the lower cylinder. Just something to consider in chasing this down.

Do you have access to an inductive timing light? if so, while the motor is running, clip onto each plugwire in turn and study the flash. Both equal in intensity and firing pattern?..no skips?...If that is good for both cylinders, check the plug boots and terminal wire < inside the boot> connections. If that's good as well and the spark 1/4" open air gap jump, then your ignition sounds up to par.

Water beads will sometimes be evident on the spark plugs < sometimes not > if you have water intrusion.

 

[2shallow2sail]

Re: OMC 15hp Running on one cylinder

SureShot- I only have one carb on this motor. It could be flooding the bottom cylinder, but it was running perfect and I have not adjusted it. The float looks to be set correctly. I used to have the same problem as you with the #2 hole firing at higher RPM's. I found that the point was set at 0.010" on that one, adjusting it to 0.020" corrected the problem. Mine will not currently run at all on the lower cylinder even at high RPM's.

AITn- Yes the whole pump is brand new. I tried to rebuilt the old one but the valves were shot. I have not taken apart the new one in fear of screwing it up putting it back together. I will ask around about the timing light, I can probably find one. I don't mind buying tools that will come in handy in other applications so this may be worth while. The plug wires are also brand new since they came attached to the coils.

 

[AlTn]

Re: OMC 15hp Running on one cylinder

k...one other thing I thought of after posting..concerning the water intrustion...often the cylinder, spark plug, and piston head will appear "steam cleaned" especially compared to the other cylinder <s>...can you roll the pistons up and look inside each cylinder to determine if they appear the same?

 

[Sureshot]

Re: OMC 15hp Running on one cylinder

Whoops, forgot that minor detail. Yeah, guess it would be hard to get up to full speed if the single carb wasn't firing . Best of luck to you in figuring this out. If I learn anything when I go through my engine this weekend I'll be sure to keep you posted.

 

[Rick.]

Re: OMC 15hp Running on one cylinder

thanks Rick. The entire fuel pump is only 3 months old so I'd like to avoid taking it apart if possible (for now), those things are tricky. I actually did break a couple pieces off my slow speed knob as well, but that was in the spring and i think I got them all out but i think it is worth looking at. I have never taken off the manifold. The reeds are actually called "leafs" on the diagram correct? I guess i just need the 2 gaskets if i take it off. If the reeds are fouled, would that cause the cylinder to flood? The plug is wet so fuel is getting in there. Any tips on how to tell if water is also getting in there?


http://www.**********/parts/search/BRP/EVINRUDE/1974/15404S/INTAKE MANIFOLD/parts.html

Altn could be onto something IE: errant spark. The best way I have found to check for that is to fire the motor in the dark and look for sparks to ground. Water intrusion will usually give off a white smoke (vapor) while running. When I found the plastic in my reed my lower cylinder was so wet with fuel it could not fire. Rick.

 

[2shallow2sail]

Re: OMC 15hp Running on one cylinder

I won't be near the motor for a couple days. I am going to check:

-Cylinders to see if the lower looks "steam cleaned"
-Pull manifold and check the reed valves
-look into getting my hands on a timing light

Any other ideas?

 

[Rick.]

Re: OMC 15hp Running on one cylinder

Pull the manifold last. I'm going to feel like a jerk if you go to all that trouble and I'm wrong. You must use an "inductive" timing light. Cable clamps around plug wire rather than plugging it inline. Reeds are not normally a problem but I guess I'm not normal. Rick.

 

[2shallow2sail]

Re: OMC 15hp Running on one cylinder

I've taken the starter and carb off so many times that the 5 extra bolts on the manifold won't be a big deal. Plus 3 bucks for the gaskets, might as well take a look and rule it out. It looked like a little fuel was pooling in the bottom of the airbox, and i thought it was flooding (though it was not nearly as much as when the float was sticking in the spring). Is fuel coming back into the airbox also a possible symptom of a fouled reed?

 

[AlTn]

Re: OMC 15hp Running on one cylinder

yes

 

[OptsyEagle]

Re: OMC 15hp Running on one cylinder

Some say you can take the manifold off without taking off the powerhead but I know I couldn't do it. There is a bolt in the bottom portside of that manifold that is almost impossible to get at while the powerhead is on the midsection. If you do take it off, replace the lower crankcase seal. That could also be your problem but the powerhead definitely needs to come off to do that.

If your reed is not closing properly it can spit fuel out of the carb throat and of course your cylinder will not work well if at all. Since the problem stayed with the same cylinder when you changed the coils you can probably eliminate spark, timing and you can eliminate your carb, since it feeds both cylinders.

You could also try and disconnect the fuel pump from the powerhead (2 screws) and compress the primer bulb and see if you see any fuel dripping out of the back that may be flooding the cylinder. As well, take a close look at the fuel pump gasket that seals the pump to the powerhead, to see if it is in good condition.

 

[2shallow2sail]

Re: OMC 15hp Running on one cylinder

If the powerhead has to come off to get at the manifold, I will probably wait until next winter to tackle it in the basement as I have already spent too many sunny days working on this engine and not sailing. I believe that Leeroy has detailed descriptions of that process. I'll try some of the other checks suggested in the thread in the meantime. Can anyone else confirm that the powerhead has to come off to get at the reeds? Since I have good compression is all this effort worth it for this motor? It was running like a clock 2 weeks ago

I am going to buy either a Nissan 3.5hp 2stoke or a new Suzuki 2.5 4S to use on my other dink and I can use it for now on the big Avon in place of the Johnnyrude.

 

[Rick.]

Re: OMC 15hp Running on one cylinder

I can't remember if you have to pull the power head or not. I know I did. Just wanted to say mine ran like a top too. Then in a instant it ran like crap and fouled the lower plug. As I remember I had laid it down on it's side to transport and the plastic must have moved and then sucked into the reed at start up. I feel your pain re sunny days and working on motors. That is what winter is for. Rick.

 

[OptsyEagle]

Re: OMC 15hp Running on one cylinder

Leeroy's rambles does indicate that the manifold can be removed without the powerhead coming off but to verify for yourself, just take a look at all the bolts. There is one at the bottom, on the portside, that is so close to a curvature of the bottom pan that for the life of me, I cannot remove without taking off the powerhead. Maybe you can jerry rig up a wrench or socket or something, but I took it off. If you do, I would also change the upper water tube grommet as well. If tends to deteriorate in time and is not expensive, so replace it.

Check to see if you see any fuel spitting out the front of the carb throat when you are running it. If there is then you most likely have a bad leaf valve and if it doesn't you may have a bad leaf valve.

 

[2shallow2sail]

Re: OMC 15hp Running on one cylinder

Thanks, i will take a look at it this weekend when I am at the boat. Maybe I can grind a wrench down to fit. If not ill pull the head over the winter, or if we get a rainy weekend. I DO SEE FUEL pooling in the bottom of the airbox when running, so hopefully that means its the leafs and is fix-able. Can you clarify your last sentence? I am confused... thanks again!

 

[OptsyEagle]

Re: OMC 15hp Running on one cylinder

Depending on how much the leaf valve is restricted, one can sometimes have a bad leaf valve but still not see much in the line of fuel from the carb throat. Since you are already observing fuel in the airbox, it seems to me that a faltly leaf valve is most likely the problem.

 

[CatTwentyTwo]

Re: OMC 15hp Running on one cylinder

I don't know the answer to this so I'm just throwing it out there as a question. The OP is getting 110 psi on both cylinders, would that still be the case with a bad reed valve on one of the cylinders or would one be expected to read lower?