KZ650 Issue: Engine restricts itself during rides

Hey Guys,

I am new to the forum and I am hoping you might be able to help me with a problem I am having with my 77 KZ650. The problem occurs while riding and has happened when the engine is cool and hot. The engine will be running normal but then will "kick" into a restricted state where you can maintain your current speed but you have to be at full throttle. If you throttle down, you will never get back to your original speed and the bike sounds as if its maxed out and running at full capacity.If you pull the clutch in the bike wil mechanically shut off (electricals will remain on).

This used to just occur when I hit a hard bump. Now it is completely random when it happens. Sometimes if you pump the throttle a handful of time it will kick out of this restricted state and other times it will randomly do it itself. There have been times where once it gets there, it never comes out and I have to let it sit for a few hours.

The carbs were rebuilt by a professional and i replaced the petcock with a new high flow petcock as I thought it might be a gas problem.

Any info or advice is absolutely appreciated as I am tired of pushing the bike down busy streets! Thanks!

It sounds like one or two cylinders may occasionally stop firing. I would carefully check the wiring to the coils to make sure there are no loose or corroded connections. Also check to ensure that one of the coils isn't grounding out against the frame. When is the last time you replaced the points? Maybe one set is pitted really badly and failing intermittently (unlikely, but possible). Ed

I would check the battery w a digital multimeter --- it should be 12.6 VDC after charging.
Even if it's new check it. The bike needs a good battery to fire the coils & run right.

AmishGuy wrote: Hey Guys,

I am new to the forum and I am hoping you might be able to help me with a problem I am having with my 77 KZ650. The problem occurs while riding and has happened when the engine is cool and hot. The engine will be running normal but then will "kick" into a restricted state where you can maintain your current speed but you have to be at full throttle. If you throttle down, you will never get back to your original speed and the bike sounds as if its maxed out and running at full capacity.If you pull the clutch in the bike wil mechanically shut off (electricals will remain on).

when mine was doing that it was because there was crud in the fuel tank and a bit of it would get into a main jet and block it. If fuel system has any crap in it, you will have problems forever.

Could also be symptoms of an electrical problem maybe a bad coil? This part sounds like a bad coil.

There have been times where once it gets there, it never comes out and I have to let it sit for a few hours.