I have an '83 Suzuki DT115 jet that overheats above idle.
Last year while attempting to help someone out on the Big Su I ate a little gravel. Not too bad, or so I thought after cleanining out the grate. After that incident, after about 5-7 minutes of running on step--about 4300 rpm--it starts spitting steam out of the "piss hole" but as soon as I back the throttle to idle I get a good steady stream of water again. It hasn't gotten hot enough to set off the alarm so I'm not worried about damage (yet)
I tried blowing it out with air and with water but no joy and I also dropped the jet to doublecheck the water pump impeller, flanges an gaskets. Other than a couple of tiny nicks on the pump impeller everything looks good. I assume (and fear) I have a pebble or two blocking water flow inside the power head.
Any suggestions are welcome
I owned an '83 Suzuki 140 with a jet. I had the same problem. Many gaskets, thermostats, etc. were replaced by the dealer. In the end, that model has a rubber gasket/seal between the top of the tube on the water pump and the connecting tube in the vertical engine housing. It had become worn and was completely missing. It cost about $3 ten years ago and solved my overheating problem. The Suzuki 115s and 140s are kissin' cousins. Check to see if your rubber gasket/seal is there.