1988 15 Hp Johnson - intermittent start

[SShuttle]

Sometimes it starts, usually it doesn't. Replaced the power pack with new Mallory after trouble-shooting suggested it was bad (appeared to spark weakly when tapping on old power pack but not at all otherwise). Initially wouldn't start with new pack. Removed new pp and both coils and wire brushed all ground contacts. Reassembled and it started right up and ran great at idle and open throttle during a 30 minute ride . Killed and restarted repeatedly. Today, two days later, won't start. Blistered hand pulling and used cheater fluid (ether sprayed in carb). Started once after about 20 pulls but I stalled it putting it in gear and it never fired again after about 100 more pulls. Not even a burble. Gotta be spark. Plugs look great, slightly wet with fuel but no carbon (don't think its flooding with the ether boost). Plug wires are in good shape, though not new. Will test tomorrow night when I can get a buddy to watch for spark leakage after dark. The electronics under the flywheel, which I call the timing sensor and pickup (probably not the right terminology) are clean and wires are in good shape. There is evidence of potting that ran out of one or both of those two components, but it has been like this for years and this problem if failry new after a year of not using the engine (I know, kiss of death). Fuel system is good. Just flushed the tank and all lines a month ago and it runs well once started.
Any other suggestions?

 

[HighTrim]

Re: 1988 15 Hp Johnson - intermittent start

Welcome to iboats. First off, never spray anything other than premixed fuel into the carbs. I would start with getting an inline spark tester and compression guage to determine if I was in fact getting a bright blue spark to jump 7/16 of an inch with a ZAP!! and had a viable base to work with in regards to compression. If all is well there, I would move on to fuel delivery. And by the way, what is your starting procedure, step by step?

 

[SShuttle]

Re: 1988 15 Hp Johnson - intermittent start

Starting procedure:
Put in water or attach water muffs with running hose.
Pump fuel tank bulb until firm.
Set throttle to max, which is slightly more than idle (limited by shift cam in nuetral).
Pull choke all the way out (at least for first several pulls).
Pull cord until engine starts or my chest hurts.

Thanks for the help!

 

[HighTrim]

Re: 1988 15 Hp Johnson - intermittent start

Here is the spark tester I was referring to



And here is some reading. When was the carb last rebuilt? Let us know what you find.

http://forums.iboats.com/showthread.php?t=225510

http://forums.iboats.com/showthread.php?t=158071

 

[SShuttle]

Re: 1988 15 Hp Johnson - intermittent start

Thanks HighTrim, I will try to find a spark tester and compression gage. (No respectable mechanic would be caught without these in the garage anyway!) Used to borrow both these tools from a friend years ago when I worked on an old cars, but haven't needed them since.
I read the cold start procedure and think I'm doing pretty good (except for the cheater fluid). Is that a bad thing because it dilutes the lubricating oil in the pre-mix, potentially causing excess wear? Is it OK to spray a little premix into the carb to ensure fuel is getting to the combustion chambers? This eliminates fuel problems from the equation and points to spark (as long as you don't flood).

OK - will get back with some data next time.
Thanks again!

 

[SShuttle]

Re: 1988 15 Hp Johnson - intermittent start

Sorry but real-life somehow got in the way of my outboard engine repair. Here's the data I collected:

Compression cyl 1 = 115 psi, cyl 2 = 113 psi

No visible spark on either plug. Tested with spark tester, plug installed as well as holding plug directly to ground.

Don't know if the rest of this is meaningful or not but I measured resistance from each pin in the power-pack to gnd and to each of the other pins with everything disconnected. Did similar for coils, ignition timing unit (?), and magnetic pickup (?). These last 2 parts are the electicals under the flywheel. Should I post these resistances?

Also checked kill switch on end of steering till. (infinite resistance when not pushed and near 0 when pushed hard). Works perfect and does not stick.

I have not found a good manual yet. How do I isolate the cause of the poor spark?

 

[HighTrim]

Re: 1988 15 Hp Johnson - intermittent start

Your compression is good, that is good to hear.

To test for no spark follow the steps below.

1. Disconnect the black yellow kill wire and retest. If the engines now has fire, the kill circuit has a fault-possibly the keyswitch, harness or shift switch.
2. Check the stator resistance. You should read approximately 500 ohms from the brown wire to engine ground.
3. Check the DVA output from the stator. You should have a reading of at least 150V or more from the brown wire to brown/yellow (while connected to the pack).
4. Check the timer bases resistance from the black/white wire to the white/black wire. Reading should be 10-20 ohms or 38-42 ohms.
5. Check the DVA output from the timer base. A reading of at least 0.5V or more from the black/white wire to the white/black (while connected to the pack) is needed to fire the pack.
6. Check the cranking RPM. A cranking speed of less than 250-RPM will not allow the system to fire properly.
7. Check the DVA output on the orange wires from the power pack while connected to the ignition coils. You should have a reading of at least 150V or more. If the readings are low, disconnect the orange wires from the ignition coils and reconnect them to load resistors. Retest. If the reading is now good, the ignition coil are likely bad. A continued low reading indicates a bad power pack.

 

[SShuttle]

Re: 1988 15 Hp Johnson - intermittent start

1.) My kill wire is gray, but I did this test with no change.
2.) I have infiniite resistance to ground on both the brown and brown/yellow wires coming from the magnetic pickup (stator?). Reading between the brown and brown/yellow wires there is only 2 oms resistence.
With pp mated, brown to gnd is 10 oms. (still way low - does this suggest a bad stator?)
3.) Not sure how to check this. Are you saying connect to pack and pull the start rope while measuring voltage? Where do I probe if the connector is mated? Do I need a special meter (DVA?), I'm using an analog VOM.
4.) Only reading 0.1 oms between white/black and black/white.
With pp mated read 27 oms.
5.) Same basic question as 3.)
6.) I have a manual pull start and I can spin it pretty fast.
7.) Same basic question as 3.)

Thanks again for the assist!