72 Johnson Sea Horse 6HP: Running Poorly: Ign Miss? Carb?

[redheaddiesel]

I have a 72 Johnson seahorse 6hp long shaft on a 12? jon boat. The problem is that it lacks power/ is running poorly. I?m not sure if it is a miss or a carb issue. I have a lot of hours invested in trying to fix this with no success. I?ll try to describe the symptoms and some of the history:

o The poor running is kind of like when you are dialing in the high speed air mix of a chainsaw: when you get it too rich and it is no longer ?screaming? with clean power and begins to flubber and lack power?only this is a very inconsistent flubber.

o It does it at all RPM?s

o At high speed it sounds like: ?ehhhhhhhh rrrrrr ehhhhhhh rrrr ehhhhhh unghhhhh rrrrrrr unghhhhh rr unghhhh

o At idle it is more like ?bum bum bum g?du g?du bum bum bum?

o At each point where it bogs ( the rrr/unghhhh and g?da) the powerhead shakes to the side like a twitch or tick

o It never happened when I first got the boat a couple of years ago. Then it would happen after about 20 minutes of running. Then I?d get a few minutes of clean running before it happened. Now it is immediate. Perhaps it is temperature related?

o The electronics were supposedly replaced five or six years ago before sitting three of four years. (they look pretty new)

o When I got the boat I disassembled and cleaned the carb (with a kit, including the metal plug) and put two fuel filters on the line. It ran well for a while. Since this problem has developed, I?ve gone through the carb a bunch of times (can of cleaner and compressed air) and makes no difference. (But I haven?t used any wires/pipe cleaner tools)

o I?ve since cleaned and adjusted the points.

o One strange occurrence: I was running 87 octane w/ ethanol when I first got the boat (for a couple of years/but not a lot of boating). In June, when the boat began to act up, I emptied the fuel and switched to 93 no ethanol. As soon as the 87 ran out of the line/carb and the 93 entered, the boat ran the best I?d ever experienced?.for about 20 minutes. Then it went back to more of the same, just slightly less severe.

o If I slowly pull the choke closed while running it makes virtually no difference until it is mostly closed where it just bogs down.

There is probably more info I should be giving and haven't. Let me know if this is the case.

Any thoughts or suggestions as to what to do next or what the problem might be would be highly valued.

Thanks in advance,
Matt
Chattanooga, TN

 

[Daviet]

Re: 72 Johnson Sea Horse 6HP: Running Poorly: Ign Miss? Carb?

Start with the basics, compression and spark test. The spark should jump a 3/8" air gap and be bright blue. If those check out move on to the fuel delivery system. Make sure the fuel pump is working properly, remove the carb and make sure all the passages are clean, paying attention to the high speed jet and the passages under the core plug on top of the carb. Make sure the float level is correct. If the fuel lines haven't been replaced it would be a good idea to replace them.

 

[The Famous Grouse]

Re: 72 Johnson Sea Horse 6HP: Running Poorly: Ign Miss? Carb?

I'm going to guess it's an ignition problem. Especially since you've tried the fresh fuel approach.

Plus, generally if you can get it up to speed, I haven't seen a carb problem that will "come and go" like you're describing. IME, carb problems make it hard starting, won't idle, bogging down when throttling up, etc, but they don't usually cause sudden misses while running at higher RPM like you describe..

It really sounds like your engine is missing, which points to an ignition issue.

The problem with saying the "electronics" were replaced is to know which parts? Points? Coil? Condenser? Plug wires? All of the above? 2 of the 4? You just can't be sure, therefore they're all suspect.

If you're willing to play trial and error, you could tear it down and look at the coil / condenser to see if one looks newer than the other. I'm always hesitant to recommend parts changing though, I think it's cheper to take it to a mechanic who knows what he's doing.

Grouse

 

[Tim Frank]

Re: 72 Johnson Sea Horse 6HP: Running Poorly: Ign Miss? Carb?

My gut reaction would be coils....especially if they are original.
But if you use the FAQ section on ignition troubleshooting you should be able to zero in on exact issue.

Step one as stated would be compression and spark test....check spark with spark tester, not "leaning plug abainst block".

 

[redheaddiesel]

Re: 72 Johnson Sea Horse 6HP: Running Poorly: Ign Miss? Carb?

Additional info: The coils, condensers, and points all seem relatively new: i.e. none look like they go back to '72. They are definitely at least five years old, though, even though I don't think they have a lot of hours on them.

All the times I cleaned the carb, I never took out the main jet (in the bottom of the float bowl, right?) because I didn't have a screwdriver that looked like it would take it out without buggering it up. (Narrow shaft with a fat blade). I did put cleaner and air through it, though.

On the high speed missing/sputtering--it is fairly consistent. Not like a pattern, but doing it the whole time nevertheless. It is like it is just about to "break out" into high RPM's/full power but something is bogging it down erratically. It used to run great for a short amount of time before this has happened, which makes me wonder if it is a temperature issue--as it heats up the problem kicks in (electronics? reed valve?). My grandpa also thought maybe sediment in the carb was getting stirred up, but, unless I'm missing something (main jet or under that plug) it doesn't seem to fit.

By the way, can I take that plug out again and replace it without having to buy another full carb kit with a new one?

Hope this helps.

Matt.

 

[redheaddiesel]

Re: 72 Johnson Sea Horse 6HP: Running Poorly: Ign Miss? Carb?

replaced points, condensers, coils, and plugs. The boat is now running superbly. Thanks everyone for the help.

Matt.