Spark-check...Compression-check...Fuel-oh Yes...no ignition on #3/4

[tom203]

"The cap resistance was 5 Ohm, I couldn't get a reading on the secondary (a 1 on my meter = OL) in any range on the DMM on the left (1/4) coil, but this might be an issue with getting poor contact with the probe. That coil is suspect anyhow, as back in the fall, the key was left on and that coil overheated.

"
You should be able to measure secondary ohms easy- I just checked my spares and got 32k ohms across spark plug connectors. Try moving up two ranges on meter and retest.
The overheated coil brings up the possibility of that coil (or its ignitor circuit) changing as it heats up- this seems farfetched though, I would think it would just fail and not make any spark ever again.
I use fogging oil on outboards- it seems to disappear asap.

[BigD_83]

I had a closer look at my plugs, and they are definitely OIL fouled. A shiny black that didn't clean up with a vinegar bath. I put in a set of new D8EA plugs, put them in, primed the carbs, and fired the starter. I got what sounded like ignition on two cylinders, then the engine died. Two tries after that, same thing as with the old plugs....no ignition.

I pulled the plugs. They were a little wet (gas).

I then checked the spark against the head. All four plugs are now sparking, but they do seem weak, more like a bright white small flint spark than a broad blue spark. I've put the battery on the charger overnight, and we'll see how it goes in the morning.

The DMM seems to have some issues. I couldn't even get a reading across the battery terminals. This might be the reason I'm having trouble with readings on the coils and wires.

[tom203]

Low battery in multimeter will produce erratic readings. Also make sure you have decent voltage (orange/white wire to good ground) at ignition coils- mine still worked ok during cranking with weak battery,but at some point ignitor is not likely to be happy.

[BigD_83]

Low battery in multimeter will produce erratic readings. Also make sure you have decent voltage (orange/white wire to good ground) at ignition coils- mine still worked ok during cranking with weak battery,but at some point ignitor is not likely to be happy.

Thanks for the tip about the ignitor, I'll get on that today.

[BigD_83]

I checked the multimeter and it was a broken off tip causing problems with the readings. Replaced the leads and it was back to normal

Voltage at the coils: key on. Battery 12.8V, + at coils 12.1V
cranking voltage: Battery: 11.9V Coil 9.8- 10V

The question is: are these voltages too low, and is the drop when cranking too much?

Do these numbers suggest a weak spark might actually be the problem?

I pulled the carbs yet again and double checked that I had free flow through all passages, and poked around the fuel uptake tubes with a small wire. With compressed air I was getting a really nice mist out the engine side of the carbs and not a single passage was plugged to carb cleaner spray.

I still was getting no firing in the cylinders with a known good battery.

I had one backfire in #2 cylinder (only plug with a colour change at the tip) and smoke coming back out the airbox. This was with the air filter and lid removed while seeing if it made a difference. Scared me enough that once I was convinced I didn't have a fire, I came inside to watch the Canucks/Kings game

[BigD_83]

After the frustration that was the end of the Canuck's season, I went back to the garage to triple check resistances. I had this nagging doubt that the overload reading I was getting on the 1/4 secondary resistance was just, well...wrong. Turns out it wasn't, and it explains the earlier issue with #1 cylinder not firing.

I pulled all of the plug caps off, which I have done before, and thought I had retrimmed them all. Turns out, I had done the leads for 2, 3, and 4, but not that of #1. The end of #1 lead was shiny and hard, but there was almost a "glue" on the outside.

Here are the numbers from tonight:

1/4 secondary with caps: OL
1/4 secondary without the caps: 11.52 kOhm
# 4 cap: 8.0 kOhm
OLD #1 (stock) cap: 1.6-1.9 MOhm (oh oh!)
NEW #1 (NGK) cap: 4.8 kOhm

New 1/4 secondary resistance (with caps) 24.3 kOhm

Compare that to 2/4 readings with and without the caps:

2/3 secondary (no caps): 12.18 kOhm
#2 cap: 8.3 kOhm
#3 cap: 10.6 kOhm
2/3 with caps: 32 kOhm

Primary resistances:

1/4 coil 4.5 Ohm
2/3 coil 4.3 Ohm

Too late to get into trying to start it up, but I should at least get better spark on #1 now.

Is there any danger in using regular (non-resistor) plugs with the secondary resistance that low?

[tom203]

I'm under the impression that coils with stock caps have about 32kohm secondary, while coils with ngk caps have about 24kohms, so no problem with D8EA plugs.

[BigD_83]

Thar she blows! Combustion on all four cylinders

The sweetest sound you ever heard, was a GS starting up on the first attempt...

First thing I did tonight was find the leak in my girlfriends Thermarest, and then I switched into garage clothing and headed to the garage.

It wasn't quite the FIRST attempt because I hadn't primed it long enough, but she fired on ALL FOUR CYLINDERS on the second hit of the starter. Shut down, start up, repeat. Run it up and down the laneway, park it, let it sit. Starts up!

Turns out the bad plug cap was the fly in the ointment. Goes to show that you need to check, double check, and sometimes, triple check.

I think I can call it a success, and end the thread.

Thanks for all of the suggestions. Each and every one was investigated and seen through. Now it's time to move on to another highest idle and vacuum synch. I only have two weeks to get it ready for a May 5th ride.

Wish me luck.