EDIT 9/12/17: Problem turned out to be a sticking throttle position sensor. When the sensor warms up, it doesn't return to the idle position and causing the engine to stall. Read below to see all the tests performed and for how to build a peak voltage detector circuit. Part ordered and replaced.
I have been chasing a stalling issue on my 2008 Suzuki King Quad 750AXi for a while now. I have done a lot of reading and research, so I thought I would put together a thread that combined all that info in hopes it will help someone else. There is a lot of good info on here and I want to thank everyone for their contributions. They have kept me searching.
Details on the machine:
2008 Suzuki King Quad 750 AXi
HMF Performance Slip-On
HMF Fuel Optimizer (Set to factory settings)
NGK CR6EIA-9 Iridium Spark Plug
Factory Air Cleaner
3154 Miles, 409 Hours
Coolant flushed and changed, Oil Changed, Front and Rear Diff Fluids Changed
Warn 2500lb winch, LED Pod Light Bulb, Heat Demon Grips, 126W Light Bar, 2x 27W Work Lights
So this issue started 2 years ago. Quad cut out and wouldn't restart until it cooled. I thought it was the spark plug at first. So I replaced it with the iridium plug: https://www.suzukiatvforums.com/forum...g-upgrade.html
This did not fix the problem. I thought then I didn't seat the boot well and water was getting in the plug. I used dielectric grease and sealed everything up. It still did it.
After reading, I turned to the fuel system. I replaced the fuel filter and did the screen mod on the pressure regulator to bump the pressure a bit: https://www.suzukiatvforums.com/forum...mp-repair.html
I also cleaned the fuel injector. It began to idle much smoother.
It worked fine from here on out. Fast forward to last fall/winter. After coming to a stop, it would just kick off and then it would fire right back up. This was annoying but not really detrimental. And when I used my light bar and work lights they would flicker to the RPM which was annoying. It still had the original battery, so I put a new one in. No change. After some more reading I came to the ground regulator mod: https://www.suzukiatvforums.com/forum...lator-mod.html
It is also related to this issue: https://www.suzukiatvforums.com/forum...dle-issue.html
This boosted my idle voltage to over 14 volts. See the ground regulator mod for my contribution. This solved the random idle stalling issue. While the machine was apart I decided to change coolant, oil, and diff fluids. With all my panels off, this worked great. The quad idled perfectly. I put everything back together and let it idle in my driveway. It idled fine. When I revved the engine, it revved and instead of returning to idle it misfired and died. I've been able to repeat this result several times.
I consulted the factory service manual and some threads on here: https://www.suzukiatvforums.com/forum...ut-10-min.html
So I started hunting. TPS was in range and I did not have any service codes.
Easiest suspect was that the coil pack was overheating because it sits above the exhaust. I remove it, cleaned all the connections up and replaced with no change. I measured the resistances and they were all in check... 0.1-0.6 primary ohms and 12k-19k secondary ohms. These were measured when the coil was cool. I ordered a new one from Caltric: Suzuki LT-A750X KINGQUAD 750AXI - 2008 - Ignition Coil
It was cheap, but complete. This should at least tell me if the problem was the coil. No one had one in stock nearby.
I installed it and there was no change in the issue. The new coil measure correctly on the primary but I only got 3k ohms on the secondary. I may not have made a good connection but I figured i'd try it. It fired right up and drive great. I let it idle in my driveway and it shut off. I was frustrated to say the least. Time for more reading.
I was following 1H-3 to 1H-6 in the service manual and the troubleshooting codes for C12 (SKP sensor) and C24 (ignition coil) neither of which were displaying since I did not get a check engine light. I checked the resistance of the CKP sensor and it was 220 ohms, right within spec of 150-250 ohms. I did this test while the engine was hot just after cutting out.