One cylinder spark

[Smoen55]

2001 txt 295 Robin with recent no spark. Just like every one else with this problem I've been chasing issues. I replaced the CDI and coil with the cheap stuff and received junk as usual as still had no spark. I read a lot of good suggestion on this forum and put the old CDI back in with a coil that I spent a bit more money on but is probably still overseas crap. However it is running now but with spark to only one side so I obviously am lacking power. Is this still a bad coil issue. My understanding is that both plugs fire at the same time regardless just like my Harley. So is it possible this coil is half good and bad at the same time. Thanks

[Cartmaster]

You are correct that both plugs fire at the same time but no, If the coil is bad neither plug should spark due to the way the coil is wired internally. Unlike an auto coil the high tension has no internal connection to ground until both plugs are grounded. Lack of spark on one cylinder is more likely to be a plug failing or the lead or cap is tracking to ground. How are you checking for spark? When checking,
both plugs should see ground or you will not get a spark on either plug. Have you checked your compression on both cylinders?

If you have an ohm meter take a reading across both plug leads. You are looking for around 17-20k ohms but anything over 10k ohms should work.

[Smoen55]

I'm checking spark by pulling plug and holding close to ground. The long wire fires like it should and short side nothing. FYI I have ordered a spark tester and it will be arriving tomorrow. Coil ohm's at 11.95 through plug wires. Compression is not great but at 110ish both sides. I have not adjusted valves as I know I only have spark on one side at this point. I can switch wires and it will fire on the long side even without the other wire plugged on the other side. I thought it was a carb issue last night and cleaned the carb today and discovered the one side only spark issue when it actually ran better, however not the way it was prior to all the no spark issues.

[CP241]

Forget the spark. 110 compression it’s a wonder it runs at all. You need to fix that long before you start worrying about spark.

[Smoen55]

Well I purchased that compression tester through Amazon but prior to the no spark issue the cart ran good with plenty of power and with four adults on it. That's why I'm not very concerned with the compression at this point. I just need to figure out why I'm only getting spark to one side now after the no spark episode. It just doesn't make sense and know others have had this phenomenon.

[CP241]

Even with a cheap crappy compression tester I’d be concerned with 110psi.

As for the spark issue i think it’s a user problem. The way these coils work either they work or they don’t. No spark out of only 1 cylinder really is unlikely. As fartmaster said maybe a bad plug or plug wire. But the coil either works in both or it doesn’t work.

That said I’d be much more concerned about 110psi. Low service limit is 140psi. Good engine is 160+

[Cartmaster]

As CP241 says, you need to figure out compression regardless of how well it runs/ran. Check valve lash, its a 5 minute job!

Originally Posted by Smoen55

I can switch wires and it will fire on the long side even without the other wire plugged on the other side.

This should not be happening. The HT circuit is not complete with only one plug connected. There is either a short circuit inside the coil or the other output is tracking out somewhere. Look for continuity between the plug leads, small terminals and the core of the coil. You should get NO continuity at all. you should get around 3 ohms across the small terminals, you have good ohms between the HT leads so that part is good.

Where is the other lead laying when you get spark only on the long lead?

Have you had both plugs grounded to the head at the same time when checking spark?

Have you tried doing this in the dark to see if the coil or short lead is tracking out before the plug?

[Smoen55]

Checked lash and compression improved to almost 160 but not quite there. Still only spark out the one side of coil. I switched the plugs and they both will spark on the long lead. Which tells me plugs are OK. Ohm's on the coil terminals is 4.3 and it doesn't seem to be visibly arcing out anywhere as I was working on it in the dark last night. I absolutely hate electrical issues. I would much rather tear into a rebuild than figure this crap out. Regardless it's not not going to run firing on one cylinder either.

[CP241]

It’s either a bad wire, or a bad coil inside where it connects to the wire may have high resistance when a load is applied to the wire. Remember that all you need is one strand of wire to have good continuity and resistance. But once you load the circuit and apply a load (current) through that one strand it’s not going to work.

The wires should be replaceable from the coil. They should attach to what resembles a wood screw. Sometimes when not assembled properly the strands inside the wire get pushed up funny and don’t make good contact with the screw. You can cut a half inch off the cable and reattach it to the coil

[CP241]

To rule out a bad wire you can also switch the long and short wires and see if the short one still doesn’t have spark. If so then you know the short wire is bad.

If you switch them and now the long one doesn’t have spark then replace the coil it’s something inside with a bad connection.