High-tech Spark Tester

[Lakesailor]

I have something like that somewhere, in a fetching electric blue, but you can't tell what the air-gap is and the iboats forum keeps mentioning a 7/16" air-gap as the desirable test.
The wood has been in my bits bin in the garage for over a year so should be nice and dry.

 

[VicS]

[ QUOTE ]
but you can't tell what the air-gap is

[/ QUOTE ] The object of these things is that you fit then in line with the plug and they light up as the plug sparks while the engine is actually running. That way you will be able to see, by testing one cylinder at a time. which one is missing if it is an ignition related problem. Much the same as using an inductively coupled timing light as suggested by andyball. Not only will it confirm that the problem is ignition related but it pinpoints which system to look at. Then you can swap the ht coils around to see if it is one of them or whether you have to consider that it is the powerpack. (you have already replaced the plugs havent you?)

 

[Lakesailor]

I can test the presence of a firing spark by the time-honoured shock-up-the-arm technique of pulling the caps whilst it's running. Reading the iboat forums I found that Johnson recommend that the test using a 7/16" air gap will show that you are getting the correct HT discharge.
Another thread covers the suitability (or not) of equivalent non-champion plugs. I've just installed some new QL77JC4s.
I'm doing these tests on the mooring to eliminate certain items which I don't particularly feel are causing any problem. But I'm not going to strip the carbs on the water, so if these tests show everything hunky-dory I'll bring the boat off the lake and do the carbs.
It seems to me that most outboard problems are the result of years of neglect and straightforward servicing and testing can avoid the problems.
When you but a secondhand motor it seems you need to assume that nothing much has been looked after.

 

[VicS]

Your makeshift tester will check the correct voltage is being generated fair enough and the "time honoured method" will identify a cylinder which is not firing but it may not id one that is just occasionally missing. The gadgets I suggest will enable you to watch what is happening while you are running at all loads and speeds.

Not a good idea to use the time honoured method with electonic ignition as the volts are so high that the shock up the arm can be pretty severe. I have also seen a suggestion that it can damage the system due to very high voltage surges but I am not sure about that one.

I agree wise not to do the carbs while on the water. I did have to remove one and clean it once while afloat, at night as well, but it was a fairly simple one.

 

[andyball]

possible that the wires from the stator are a bit busted... and losing continuity when the advance mech used?

carefully watch the resistances when moving the advance, tho allow for the fact that moving it may create a small voltage to throw the readings all over the show briefly.

course, wiggling ( I'm such a techy ) the wires should reveal a problem w/o the poss of confusing the meter.


I'd also drain the carbs ( via the drain screws) & test again before a strip - lil bits of water can play funny tricks at times ime.

 

[Lakesailor]

The idea of testing under load and at revs is the next stage on, if you see what I mean. At that stage I'll get an induction timing light (my old one fell to bits) so that I don't have to hang over the stern under way!

I've just made a starter solenoid cable with a horn button to operate so that I can spin the motor whilst holding the compression tester.

I see it's sunny now so I'll go and have a go.

 

[Lakesailor]

So.
Been out to boat and tested a few things. Pulled the plug leads off whilst it was ticking over. The bottom cylinder perhaps didn't make a whole load of difference, one of them had long sparks running out of the plug cap and jumping to ground on the plug base. Oooer.
Bit tricky as you're hanging out over the stern and there's a flywheel spinning where you may grab if you wobble.

Then I fitted my starter lead to allow me to operate the starter from near the motor

This worked a treat and I did a compression test which showed all cylinders over 100 psi, which is fine according to the iboats forum.

Then I used my high-tech spark tester which in view of the voltages around I earthed using a jumper cable to the main engine earth.

This showed that all managed a spark across the gap. None as a fat blue, cracking spark as suggested, but a thinnish yellow one, again the bottom cylinder seemed the weakest.

I also took the air plenum off and drained the float chambers. Nothing particularly watery came out, just a few little drops maybe. The carbs looked pretty clean from that viewpoint. Doesn't tell me what the insides are like though. The spray back on the top carb is quite common it seems. Also this was after the spinning over without the plugs in so doesn't reflect normal running conditions.

Then fired it up and went for a run. It stuttered a bit for about 20 seconds and then smoothed out. Ran quite well, but after about 15 minutes started to run a bit unevenly at around 8 -10 mph. It would run OK at low revs and if you opened the throttle briefly it it cleaned up.

I have a feeling it's the coil on the bottom cylinder. Perhaps losing spark as it gets hotter.
The next thing is as andy and vic suggest to try something when it's running under load. Vic's devices would allow a spark comparison between cylinders, but you have to hang out the back of the boat, unless I made up some extension leads, but that introduces a whole load of variables. Andy's idea about a timing light would allow me to tape the light in the cockpit and see easily if it gave steady flashes. Trouble is I'd have to swap it to different cylinders progressively and may miss testing the one that plays up when it does so.

Testing with the multimeter will have to wait until I get a manual as I don't want to spike the wrong wires.
I'm sure it's ignition.

 

[VicS]

[ QUOTE ]
The bottom cylinder perhaps didn't make a whole load of difference, one of them had long sparks running out of the plug cap and jumping to ground on the plug base. Oooer.

[/ QUOTE ] Oooer on both points indeed. A couple of things to look at there I think.

[ QUOTE ]
if you opened the throttle briefly it it cleaned up.

[/ QUOTE ] One of the carbs flooding slightly perhaps. Or one not getting enough fuel. Do you have three separate fuel pumps or just one common to all three carbs.

Any problems with the VRO. I seem to remember that the early versions were bad and people stateside often disconnect them. Latter ones are I think OK and operate over a narrower band of fuel/oil ratios.

I must say I admire your systematic approach to all of this. Obviously not an Engineer.

 

[Lakesailor]

Ah. didn't make that very clear. The spidery sparks occurred when I pulled the cap off. It just wouldn't stop sparking!
The bottom cylinder coil is my favourite for the problem. If it shows up as erratic on the timing light test, I'll swap coils between cylinders and see if the fault follows it.
There still is the possibility it's a fuelling problem, perhaps float-related.
(One thing that I am bearing in mind is that the fuelling solenoid operates the enrichment (choke) and although it seems to be a one-shot thing, perhaps it is sticking and overfuelling. I have no evidence to suggest that can happen)
The VRO pump and fuel pump are driven by the same air engine from crankcase pressure variation. The plunger drives both pumps so if the the oil stops pumping so does the fuel. A lot of the problems attributed to the VRO pump were in reality caused by other components and settings. There are alarm sensors for both fuel pressure and oil flow. The camps seem pretty evenly split between carry-on or disconnect and pre-mix.

 

[andyball]

wrt the weaky sparks - many cdi type igns have a wire going all the way to the remote ign switch, which when earthed, stops the engine. In a lot of cases, this wire carries rather more than 12V AC and can, if damp anywhere, lead to weak sparks ( soft verges too, no doubt)

Isolate the kill & ign cut wire at the motor to be sure, or get the trusty multy meter to work again.


You do run a risk of frying a black box by removing plug caps while engine running, btw. coils too, tho not seen that myself, yet.

 

[Lakesailor]

I've seen mention of that wire. Couldn't quite see why it mattered so that makes it more clear. I found this on iboats which backs up what you say[ QUOTE ]

I have had to many issues with corroded kill switches, some of them will read 5-8 Kohms and shut off the spark.
if you suspect a kill circuit issue simply dissconect the black/yellow wire from the pack harness at the pack.
I have seen kill ciruits with high resistance break down the circuit resistance at high speeds and not at lower speeds.
be careful playing with the blk/yellow wire, its at the same potential or slightly higher than the individual coil primaries, most run around 200 volts. its non lethal but it will make ya jump.
I hate to keep saying it but if you suspect a kill circuit issure remove the black/yellow wire from the amphenol connector and retest. be careful as there will be no good way to imediatly shut the motor off. if there is an improvement in engine performance then test the switch and harness, if no improvement is noted odds are the problem is elsewhere.

[/ QUOTE ]
So I'll have a go at that black and yellow wire as well. The advice is that earthing that b/y wire from the pack stops the motor.