82 KZ750 CSR M1 parallel twin dies at 4500 rpm.

So, I was coming home from class on wednesday and I had just stopped and filled the tank when about two miles up the road it started sputtering like it was running out of fuel. My immediate thought was that when I had changed the petcock back to run from reserve, something had not seated correctly. I switched it back and forth once or twice while keeping a steady throttle position, but it still died. I coasted into a parking lot and proceeded troubleshooting. I pulled plugs, they were a little dirty and one had some white crust on the strap, but I had spark. It wouldn't run to save it's life though, so I got a ride home and went to pick it up yesterday.

Yesterday, figuring it was probably gummed up (because I haven't used an ethanol treatment for months, been putting a new tank in every day or two), I tore down the carbs for a cleaning. there was what looked like fine red sand in the jets. I thoroughly cleaned the carbs (slides to bowls) and re-installed them. Turned the key on, gave it half choke and it kicked right over (I have no working starter). I thought, "great, I fixed it".

Not so fast...

The bike idles perfectly and even runs the way it should up to almost 4500 rpm. Once there, it starts to spit and sputter (no backfiring, so it has to be running out of fuel), and if pressed further, will kill itself at 5000 rpm.

I'm think it's maybe an advance problem since it happens at a certain rpm. Any thoughts?

I do have the manual, so I can follow the troubleshooting procedures. I just figured I would bring it up here in case any of you had a better suggestion than starting at "step 1". I'm trying not to take weeks to figure this out because it's my daily transport and I'm having to borrow a vehicle till I get it back on the road.

Also, does anyone know what the compression is supposed to be? I can't seem to find it in the manual. It seems to be pretty even around 110 on my bike.

Check the in-tank filter (on the top of the petcock) for clogging...sounds like rust in the tank...starving the engine for fuel at higher rpm's...Acid clean tank. Add an in-line fuel filter. Lots of threads on here on the subject.

Yeah, sorry... I forgot to say that a removed, disassembled and cleaned the petcock. No problems there. I get fuel flow into the bowl just fine and the inside of the tank seems to be clean. Thanks though.

Daryl wrote: So, I was coming home from class on wednesday and I had just stopped and filled the tank when about two miles up the road it started sputtering like it was running out of fuel. My immediate thought was that when I had changed the petcock back to run from reserve, something had not seated correctly. I switched it back and forth once or twice while keeping a steady throttle position, but it still died. I coasted into a parking lot and proceeded troubleshooting. I pulled plugs, they were a little dirty and one had some white crust on the strap, but I had spark. It wouldn't run to save it's life though, so I got a ride home and went to pick it up yesterday.

Yesterday, figuring it was probably gummed up (because I haven't used an ethanol treatment for months, been putting a new tank in every day or two), I tore down the carbs for a cleaning. there was what looked like fine red sand in the jets. I thoroughly cleaned the carbs (slides to bowls) and re-installed them. Turned the key on, gave it half choke and it kicked right over (I have no working starter). I thought, "great, I fixed it".

Not so fast...

The bike idles perfectly and even runs the way it should up to almost 4500 rpm. Once there, it starts to spit and sputter (no backfiring, so it has to be running out of fuel), and if pressed further, will kill itself at 5000 rpm.

I'm think it's maybe an advance problem since it happens at a certain rpm. Any thoughts?

I do have the manual, so I can follow the troubleshooting procedures. I just figured I would bring it up here in case any of you had a better suggestion than starting at "step 1". I'm trying not to take weeks to figure this out because it's my daily transport and I'm having to borrow a vehicle till I get it back on the road.

Also, does anyone know what the compression is supposed to be? I can't seem to find it in the manual. It seems to be pretty even around 110 on my bike.

Compression on a 750 twin should be about 150 (new) and service limit is about 115.

Make sure the air vent on the fuel tank cap is not clogged or restricted.

Daryl wrote: I tore down the carbs for a cleaning. there was what looked like fine red sand in the jets.

That's rust sediment. Could be some things are still plugged up.

Yeah, I think I'm gonna tear then whole fuel system down and clean it top to bottom.

And thanks for the compression info. I finally found it in the manual. I might as well try it again in case I missed something. It was pretty late when I got that far. I may have left it sit a little too long and cool of a little too much.

Well... I spent all day tearing the fuel system apart. I flushed the tank, disassembled and cleaned the petcock, disassembled and cleaned the carbs, and flushed all the fuel lines. I also used gas from one of my cans instead of the gas that was in the tank and used ethanol treatment in it. Seems to run fine now.

My thanks to Grumpy Ole Artist and bountyhunter for the help.

You probably ought to install an in-line fuel filter. Vibration pulverizes the rust particles into a fine dust that can get past the screen. The sintered brass screens will prevent the stuff from getting to the carburetors.