Misfire when Hot
- Thread starter Balduccimoto
- Start date
- Location
- NYC/Long Island
I'll see about getting the CDI out of my friend's ski. But I will try the jets first because it is definitely not right. If the problem still exists then I will swap in the other CDI
OCD Solutions
Original, Clean and Dependable Solutions
- Location
- Rentz, GA
A bad CDI may definitely still spark although it us usually only slightly fainter in open air. A tester with an adjustable gap will be a better judge of spark energy in this situation.
If you haven't already, try gapping the plugs down to 0.024". It's not a fix but it is an indicator of system health. A healthy system will jump the plug gap right out of the box with zero issues.
In your case, the symptoms never improved with the swapping of fresh components but rather worsened slightly. The common denominator through all this is the wiring, grounding points, rectifier, battery and battery cables so I'd recommend giving them a once over as well, particularly the ground wire and any grounding point.
If you haven't already, try gapping the plugs down to 0.024". It's not a fix but it is an indicator of system health. A healthy system will jump the plug gap right out of the box with zero issues.
In your case, the symptoms never improved with the swapping of fresh components but rather worsened slightly. The common denominator through all this is the wiring, grounding points, rectifier, battery and battery cables so I'd recommend giving them a once over as well, particularly the ground wire and any grounding point.
- Location
- NYC/Long Island
Doesn't sound like anyone is confident that the jetting is the problem lol. I have my doubts too.
The previous owner put new JSS battery cables on. Maybe its a good idea that I check that the connection is tight to the engine block.
I haven't tried a tight gap yet. Currently the plugs are gapped at 0.030"
The previous owner put new JSS battery cables on. Maybe its a good idea that I check that the connection is tight to the engine block.
I haven't tried a tight gap yet. Currently the plugs are gapped at 0.030"
OCD Solutions
Original, Clean and Dependable Solutions
- Location
- Rentz, GA
I didn’t bite on the jetting because you said it runs well for 4-5 gallons. It may be a separate issue but I just don’t think it would present this same way.
It’s pretty common to find multiple things while troubleshooting an issue which only makes things more complicated.
The good news is, the more little items you find and fix on the way to finding the major issue, the more likely you are to enjoy the rest of the season.
It’s pretty common to find multiple things while troubleshooting an issue which only makes things more complicated.
The good news is, the more little items you find and fix on the way to finding the major issue, the more likely you are to enjoy the rest of the season.
- Location
- NYC/Long Island
I didn’t bite on the jetting because you said it runs well for 4-5 gallons. It may be a separate issue but I just don’t think it would present this same way.
It’s pretty common to find multiple things while troubleshooting an issue which only makes things more complicated.
The good news is, the more little items you find and fix on the way to finding the major issue, the more likely you are to enjoy the rest of the season.
I agree that the jetting would have a different symptom..
I can't find anyone to repair this for me. I live 1.5 hours away from the ski so its really difficult for me to repair this.
- Location
- NYC/Long Island
I rode for 15 minutes and it ran normally. It implies that the 55 psi pop-off and small pilot was the problem. I need to do a long ride to determine if it's fixed. Also needs a little tuning because it has a hesitation from idle to 1/8 throttle.
135 Main
70 Pilot
2.0 N/S
95g spring
1/2 on the low
1 on the high
135 Main
70 Pilot
2.0 N/S
95g spring
1/2 on the low
1 on the high
- Location
- NYC/Long Island
Charlie Alpha Romeo Bravo
BruceSki
Formerly Motoman25
- Location
- Long Island
55psi pop off and one screen in the flame arrestor won’t let it run.
I’m surprised it didn’t burn down on the first tank of gas with that jetting setup.
Sent from my iPhone using Tapatalk Pro
I’m surprised it didn’t burn down on the first tank of gas with that jetting setup.
Sent from my iPhone using Tapatalk Pro
- Location
- NYC/Long Island
@MADMAT I finally had a chance to get a good ride last weekend. It seems that jetting was only part of the problem. Now after 30 minutes of riding it does it again, but now it can get into the powerband and starts breaking up at 40 mph. Maybe it still is CDI. I'm going to try swapping in a new CDI or a coil and see what happens.
- Location
- NYC/Long Island
I changed the CDI and it didnt help..
I changed the coil and it didnt help..
Then I noticed that the misfires would start when I fell off and water get inside.
I inspected all of the wires and they look great. It has to be the start/stop switch!!
So I went for a ride and tried my best not to fall.. It started to misfire after 10 minutes and it misfired the entire 5 gallons in the surf. I waited to return to the ramp to disconnect the start/stop switch... AND THE MISFIRE WAS STILL THERE!
I stood there at the ramp in complete disbelief and no clue where to go from there. So I changed the spark plugs and it was perfect again! I dumped a ton of water into it. No misfires. I packed it up and went home. Next week I will try again.
I regret tossing the old plugs because I am thinking that one of that spark plugs had a damaged porcelain that would misfire when wet. A month ago I had accidentally hit one of the spark plugs with a wrench while diagnosing other problems. I am hoping that was the problem!
I changed the coil and it didnt help..
Then I noticed that the misfires would start when I fell off and water get inside.
I inspected all of the wires and they look great. It has to be the start/stop switch!!
So I went for a ride and tried my best not to fall.. It started to misfire after 10 minutes and it misfired the entire 5 gallons in the surf. I waited to return to the ramp to disconnect the start/stop switch... AND THE MISFIRE WAS STILL THERE!
I stood there at the ramp in complete disbelief and no clue where to go from there. So I changed the spark plugs and it was perfect again! I dumped a ton of water into it. No misfires. I packed it up and went home. Next week I will try again.
I regret tossing the old plugs because I am thinking that one of that spark plugs had a damaged porcelain that would misfire when wet. A month ago I had accidentally hit one of the spark plugs with a wrench while diagnosing other problems. I am hoping that was the problem!
- Location
- Savannah, GA
Listen to OCD, close those plug gaps to .024”. OEM ignition, even with a MSD Enhancer has a tendency to find a place to leak to ground once it’s too hard to jump the plug gap.
We experienced this problem when installing solid top NGK’s without gapping them, they come gapped around .030”-.032”. Motor ran great until hot, then started to misfire. Put another set in, same thing. Closed the gap, it ran beautiful.
We experienced this problem when installing solid top NGK’s without gapping them, they come gapped around .030”-.032”. Motor ran great until hot, then started to misfire. Put another set in, same thing. Closed the gap, it ran beautiful.
OCD Solutions
Original, Clean and Dependable Solutions
- Location
- Rentz, GA
Just a quick FYI on that topic; the spark output on these systems is only regulated by the spark discharge itself. If you have a short, it discharges at a very low voltage, if you have an open, it keeps building voltage until it finds, or makes, a path.
This is why cranking a ski with the ignition leads disconnected is so devastating to components. The voltage continues to increase until it builds up to a value where it either finds a leak or just breaks down the insulation itself and punches a hole to ground. If you're lucky, it's a leak in a wire or boot but it can also take out the internals of the CDI itself. Once you punch a hole in the insulation, it's done and continues to conduct to ground at a much lower point from that point forward.
Another tidbit is that while most people understand that an ignition coil amplifies the spark signal and is at a very high voltage, they fail to realize that the stator and CDI is actually outputting quite a bit of voltage as well, (actually between 150 and 350 peak volts depending on RPM). So while you are used to looking for leaks to ground on the secondary side of the ignition coil, you could actually be shorting out between the charge coil in the stator and CDI. 12 volts is easy to insulate but even 300 volts will be able to find and exploit even the slightest degradation in your insulation integrity.
I didn't even realize this myself until I was building my test bench and had to spec out the gauges. I blew up a couple 300 volt gauges and had to up-size to 500 volt units. IIRC, the manual says a charge coil outputs 248 volts but what it fails to mention is that is in a perfect scenario with properly gapped plugs, etc. In systems with broken wires, that value can build quite high.
Most healthy systems, (CDI orange wire output to coil), are outputting up to 348 peak volts. Leave the wrong wire off and that value will exceed 500 volts in a matter of seconds, short that same wire and the system may discharge at nearly 0 volts.
This is why cranking a ski with the ignition leads disconnected is so devastating to components. The voltage continues to increase until it builds up to a value where it either finds a leak or just breaks down the insulation itself and punches a hole to ground. If you're lucky, it's a leak in a wire or boot but it can also take out the internals of the CDI itself. Once you punch a hole in the insulation, it's done and continues to conduct to ground at a much lower point from that point forward.
Another tidbit is that while most people understand that an ignition coil amplifies the spark signal and is at a very high voltage, they fail to realize that the stator and CDI is actually outputting quite a bit of voltage as well, (actually between 150 and 350 peak volts depending on RPM). So while you are used to looking for leaks to ground on the secondary side of the ignition coil, you could actually be shorting out between the charge coil in the stator and CDI. 12 volts is easy to insulate but even 300 volts will be able to find and exploit even the slightest degradation in your insulation integrity.
I didn't even realize this myself until I was building my test bench and had to spec out the gauges. I blew up a couple 300 volt gauges and had to up-size to 500 volt units. IIRC, the manual says a charge coil outputs 248 volts but what it fails to mention is that is in a perfect scenario with properly gapped plugs, etc. In systems with broken wires, that value can build quite high.
Most healthy systems, (CDI orange wire output to coil), are outputting up to 348 peak volts. Leave the wrong wire off and that value will exceed 500 volts in a matter of seconds, short that same wire and the system may discharge at nearly 0 volts.
- Location
- NYC/Long Island
I confirmed today that the issue was the spark plug .. 5+ gallons in the surf without misfire. I'm positive that I caused damage to the spark plug because the problem started around the time that I hit the spark plug when working on the jet ski. I put new plugs in at 0.020" gap.
I understand the importance of the spark plug gap and voltages, but I don't think it was contributing to the problem. I read @The OCD Garage thread about this and i'm convinced that the smaller gap could act as insurance towards misfires in high compression set ups. I used to run 0.030" gap on my old limited superjet and never had a problem, but everything was new. So I will use 0.020" gap from now on.
I understand the importance of the spark plug gap and voltages, but I don't think it was contributing to the problem. I read @The OCD Garage thread about this and i'm convinced that the smaller gap could act as insurance towards misfires in high compression set ups. I used to run 0.030" gap on my old limited superjet and never had a problem, but everything was new. So I will use 0.020" gap from now on.
Big Kahuna
Administrator
- Location
- Tuscaloosa, AL
Whenever you start having an ignition issue. Change Plugs Immediately. Been there done that. We get to the point that when it hiccups, we assume it is the Plug Wires, CDI or Stator........... We overlook the obvious........