1985 Johnson 15 bogging and stalling after running fine

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Gizmobreaker

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I have a Johnson 15 hp J15RLCOB long shaft on my Catalina 27 sailboat. It has been great for the 4 years that I have owned it, with the exception that it will quit if you go from fast to idle too quickly. I learned to live with it.

This season it has learned a new trick. It will start right up and run fine, then after, say, a half hour it will begin to run slower and slower and finally quit. It will restart but not stay running. When I can get it to run, it will bog almost immediately. When it finally runs, it will bog terribly and stall if when I change throttle position, either up or down. After it rests for a while, it will start up and run up and down, but if I put it in gear it will bog and die. Finally, after much complaining, I will get it to run and it will stay running long enough to get me in to my mooring. I can't say that anything changes except time. The fuel bulb does not collapse.

I have installed 2 new coils and a power pack. The plugs are new and gapped .030". I have changed them 3 times. I don't see any arcing near the coils or the power pack.

Spark gap tester looked great at 7/16". Plugs were in at the time.

The compression is 105 on the lower cylinder and 110 on the upper. 3 pulls.

I rebuilt the carb, yesterday. I installed all the parts from the kit, except for one lead plug (too small for any on my carb) and one small white/clear plastic short stepped tube (no idea what that is for but the kit covers many carbs). No rust in bowl. The entire carb was beautiful. Looked like new. No varnish or deposits, anywhere. No dirt.

Fuel is brand new Mobil 93 octane, mixed 50:1 with new Mercury oil. Gas tank was new last year and stored empty. Brand new vented cap, just in case. Gas hose is OMC, 2 years old. I cleaned it out at the beginning of the season to make sure there were no ethanol snakes. Clean fuel only.

Roller timing is correct by the shop manual. I set the slow speed needle and it was responsive. One thing I'm unsure about. The slow speed needle does not come to an actual point. It has a blunt end. Not rounded but like it was cleanly made that way. Very small, maybe .015". Is that correct?

Other than the slow speed needle, I'm fresh out of ideas. Any help would be most appreciated. I don't want to buy a new motor because this is the only one that will fit the peculiar transom cutout on my boat.
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

New spark plug wires, too.
 

schematic

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Re: 1985 Johnson 15 bogging and stalling after running fine

Sounds like fuel starvation. Have you tried helping it with the primer ball when its bogging? Vent or cap open? Did you remove the welch plug at the top of the carb when cleaning?
 

nwcove

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Re: 1985 Johnson 15 bogging and stalling after running fine

jmo, but any time you pull a carb for a re-kit, do not assume its clean just because it looks clean. soak it in carb cleaner, push a strand of wire through all passages , blow it out with compressed air, and repeat. that way you " should" be able to rule out the carb itself. also have a look at the plugs when it bogs and stalls......dry or wet?
 

the machinist

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Re: 1985 Johnson 15 bogging and stalling after running fine

It sounds like a fuel supply problem, either the carb or a fuel pump. I have to agree with nwcove, those carbs can be deceiving unless you pull the core plugs & be sure the passages are clean. I doubt it to be a spark plug wire or wire connection, but that is so simple a fix, may not hurt to look at it also.
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

Thank you all for responding so quickly. I removed the 2 welch plugs and used Valvetect Marine Motor De-Carb for initial cleaning then soaked it in Sea Foam. I ran wire through the passages. (Yes, I read all of your LeeRoy's Ramblings!) I blew it out with canned air (no compressor on my boat, sadly), reverse to the normal flow, then rinsed it with alcohol before reassembly. I only mentioned the cleanliness because I expected to see varnish build up and at least some dirt. I did not remove the tiny lead shot plugs as they are not included in the kit. Should I try to find those?

I wish I could have looked at the plugs right when it failed but I was much more concerned with not ending up on the rocks in Long Island Sound. On the way back in I kept pumping the bulb but I have no idea if it was helping or not. The bulb did not collapse prior to the stalling. The vent is open (new cap - Moeller CARB 2 type) and I kept the cap loose all day. The pump seems fine. No dirt in the screen. All the gaskets are holding and there are no drips. I am using clear (yellow) fuel hose from the pump to the carb and it is full of fuel. I guess I need to get a fuel pressure gauge that will handle the tiny hose. My local NAPA auto parts store did not have one.

I should have mentioned that I had to use half choke to start the motor after the failure. I've never had to do that, before. I always use full choke to start the cold motor and have to be really quick to open the choke after it starts to prevent it from stalling. This time I had to ride the choke to keep it running. Unfortunately, it didn't stay running for very long - I had to leave it alone for a while before I could start it and keep it going.

I've checked the wire harness to the power pack and the kill switch. It is an old motor but everything seems (!) fine. I run a company that builds custom electronic controls so I have some experience with connectors and corrosion therein. These pins and sockets are tin plated - not the best thing for a saltwater environment but I don't see any obvious issues. Cleaned everything with Caig contact improver, anyway.
 

AlTn

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Re: 1985 Johnson 15 bogging and stalling after running fine

did you remove and clean the orfice plug < main jet > when you did the carb rebuild? jet removal tool part #317002 ~$20 makes this less risky than using a screw driver that might be a little loose in the slot. Somewhere on the forums, the dimensions are given for this tool and you can make your own. Anyway, removing this jet and physically cleaning it with a few cooper wires twisted together, or a single strand steel wire, will ensure it's clean. It really doesn't take much "gunk" on the walls of this jet to impede fuel flow.
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

I happened to have an old wood handle square shank screwdriver that fit perfectly. It's such an unusual size that it rarely gets used so it is nice and square. Bought it new in 1975.

The jet was very tight and worried me a bit but it came right out. I soaked it overnight in Sea Foam after spraying it with the Valvetect Marine De Carb. I ran a piece of 1/16" SS wire rope back and forth through it but nothing accumulated on the wire. Of course, it doesn't seem to have helped, either, so I can't really say that I did it right or wrong...
 

AlTn

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Re: 1985 Johnson 15 bogging and stalling after running fine

jet cleaning sounds thorough....fuel pump replaced recently?...added fuel filter/water separator recently?..does pumping the primer bulb have any effect when this happens?
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

I don't have a separate fuel filter installed. I bought one, then worried that the extra resistance would make it too hard for the fuel pump. Still don't know what to do about that.

Brand new Stabil Ethanol (dark one, not the pink) at the storage level, rather than the daily running, since I don't run the motor all week.

Pumping the bulb is still non-conclusive. It might have helped but I was too worried about crashing the boat to risk letting it get close to stalling. After I tied up, the motor ran perfectly (of course).

I just got back from the boat. I took off the carb and the pump. I'll go through the carb one more time and I am ordering a new pump. I'll put in a new hose from the inlet to the pump and replace the pump to carb hose, too.

More news next weekend, unless someone has a good idea for some additional tests!

Thanks, everyone, for all the support.
 

nwcove

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Re: 1985 Johnson 15 bogging and stalling after running fine

just a random thought......but when was the last time the motor got a new impeller and t-stat? just from reading your first post....you may be lacking cooling, and finding the "goldie locks area" for not to hot , not to cold, when the motor only runs for a bit then needs to set for a awhile??
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

Random is good - that's the schedule for the problem!

The impeller is only 1 year old and the stream is very strong, even at idle. The thermostat is an unknown. The stream from the motor is hot but I didn't have a thermometer with me - I had to use the calibrated finger. I didn't burn myself, which is unusual.

I'll give the thermostat a go, on Saturday. I'll replace it and boil the old one on the stove with the candy thermometer, just to see where it opens.
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

My parts order came in. The needle valve is on back order. Earlier, I asked about the tip - mine is not sharp on the end. Instead, it is blunt. It looks like it was made that way, even under magnification it looks very cleanly done. Does anyone know how it should look?
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

Today (Saturday)
I replaced the fuel line from the inlet to the fuel pump,
installed a brand new fuel pump and gasket,
replaced the fuel line from the fuel pump to the carb with new clear (yellow) fuel tubing,
reinstalled the carb that I rebuilt, again,
and started the motor. Ran like a champ. I'll test it Sunday.
I didn't get to the thermostat as the boat is on the water and the cover latch business seemed rather a PITA. Next week for that!
I'll report back after the sea trial...
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

Still wondering about the tip of the needle valve...

The sea trial went perfectly. Ran fine all the way out, sailed on the Sound for several hours, started back up on the first or second pull and ran great all the way back. Tried several speed changes just in case. Crept up on my mooring without stalling. Fantastic!

One question: I installed yet another new OMC fuel hose (tank to engine). This one was thinner and shorter - 5/16" ID as opposed to the 3/8" that I had been using. Can you think of any reason why this might make a difference? I know that the length of hose would make a difference if the pump was weak - too much resistance to flow - but I would have thought that the large diameter would have helped rather than hurt. I also noticed that the bulb (on the new hose) got very soft while I was coming in and it took 5 or 6 pumps to get it to be firm, again. I know it's suppose to get soft - this just seemed unusually so.

Last (I hope) question: I would like to add a water separator canister style filter but I'm afraid that it would add just more resistance to fuel flow. Has anyone had experience with this?

Thanks, everyone, for all the help.
 

AlTn

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Re: 1985 Johnson 15 bogging and stalling after running fine

if it ran well, I'd disregard the idle speed mixture needle tip shape...fuel hose diameter should be fine on a 15 hp. engine < max fuel pump pressure requirement is in the 2.5 psi at 4500 rpm and that diameter hose will more than meet the volumn requirement >...holding the primer bulb vertically while squeezing it may firm it up quicker for you....no experience with water separators
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

Thank you. I held the bulb vertically, arrow up. I don't know why I know about that - it must be written somewhere. Arrow points to the engine, too.

Of course, I'm somewhat nervous about the next time I take it out. I was sort of wondering if the larger (and longer) hose could have contributed to the problem if the fuel pump was weak. I'm actually leaning toward blaming the old fuel pump to block gasket but I really don't have any reason to go that way. The carb rebuild didn't help though the second attempt might have cleared out some restriction that was missed on the 1st go round. I am also confused by the general recommendations to soak the carb in cleaner while the service manual states that one should never do that as there are sealing compounds in the carb that will be dissolved. Curiouser and curiouser, as the Cheshire Cat said.

Everything that I have read leads me to believe that the pumps rarely go bad. I'm not ready to try the suck/blow test until more fuel has evaporated - I've inhaled enough toxins for one lifetime, so far.

Still wondering about the water separator type filter...
 

Gizmobreaker

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Re: 1985 Johnson 15 bogging and stalling after running fine

One more interesting clue. I am using a brand new Moeller 3 gallon tank with the CARB fuel cap. I spoke to Moeller engineering and the very nice woman took the time to explain how this cap works. It is pressure limited so that it only vents in the pressure is above 5psa or below -5psi. That would mean that if my fuel pump was weak, the tank would never vent. Interesting. I am going to experiment with a manually vented cap that I bought. My assumption is that if the old pump was weak it would run the motor but not overcome the cap pressure threshold.
 

madhtr

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Re: 1985 Johnson 15 bogging and stalling after running fine

One more interesting clue. I am using a brand new Moeller 3 gallon tank with the CARB fuel cap. I spoke to Moeller engineering and the very nice woman took the time to explain how this cap works. It is pressure limited so that it only vents in the pressure is above 5psa or below -5psi. That would mean that if my fuel pump was weak, the tank would never vent. Interesting. I am going to experiment with a manually vented cap that I bought. My assumption is that if the old pump was weak it would run the motor but not overcome the cap pressure threshold.

Let me know how that goes. I seem to be developing a conspiracy theory, LOL :)
 

nphilbro

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Re: 1985 Johnson 15 bogging and stalling after running fine

I've had both a '88 15hp and a '77 9.9 hp kickers on my boat this year and I had all sorts of fuel problems. It wasn't until I changed to a 3/16" ID hose that I was able to keep fuel constantly running to the fuel pump. Those little diaphragm fuel pumps don't have any tolerance for air.

Just a thought. Good luck.
 
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