Virtually zero power below 3000 rpm when cold

My KZ650 is not making power when its cold at low rpm. It's not from running lean as I must reduce the "choke" to keep it from stalling from an overrich condition, and the engine will run sans choke above 3000 rpm after less than 30 seconds on the road. But no matter how the choke lever is postitioned, there is almost nothing happening below 3000 rpm. I'm talking moped here and after more than 30 years of riding and nearly as many motorcycles, I have never experienced anything this weak. Or sluggish.

Any ideas? It runs fine after a couple of miles.

Have a look at the four individual arms on the choke that pull each plunger. I have had one of the set screws back out so that one cylinder wasn't getting any enrichment. It produced similar results.

Thank you for the tip, I'll have a look!

How long do you let it warm up before riding? Ed

5-10 seconds. But I've tried to warm it up for a couple of minutes and it doesn't make much of a difference - riding it makes it run good sooner.

Still sounds like it needs to just be warmed up longer. My carb inducted bikes need a few miles to run and idle right. Now fuel injected Harley idles and runs perfect right away, but the computer is compensating for a cold motor.

Not run right is OK and normal, the problem here is that it has no power and no choke position will help. Even warming it up the engine is incredibly sluggish trying to climb up from 1500 rpm, it takes forever. Once past 3 grand, all is fine. But higher than I like when engine is cold.

Check everything,
Assume nothing...

Static timing, Advancer function.
All ignition components
Reclean carbs and adjust
I know its a very broad answer, but thats whats needed , Basiclly a good tune up , then you may discover the weak link

Street Fighter LTD wrote: Check everything,
Assume nothing...

Static timing, Advancer function.
All ignition components
Reclean carbs and adjust
I know its a very broad answer, but thats whats needed , Basiclly a good tune up , then you may discover the weak link

Exactly Right!! and start with the simple things first

What spark plugs are you using? Ed

Excellent question, Ed. They are new. It's all I know :blush: But they could of course be a range too cold.

I better do a full tune-up, which was in the plan for the first rainey weekend. And it's raining :laugh: Going to fit the proper ignition plate from the spare bike and do a dynamic adjustment. Will also check carb balance, the enrichment mechanism, compression plus adjust the cam chain. Valves must wait until I get the cover gasket - unless it's low on compression, of course.

Thanks to all who chimed in!

The reason I asked about the plugs is that the first edition of the KZ650 Kawasaki Service Manual recommended plugs that were 1 heat range too cold. I'm guessing they worked fine for the Kawasaki test riders who probably ran the the bikes at 9,000 rpm all the time. Anyway, the later editions of the manuals made a correction stating the correct plugs are ND W22ES-U or NGK B7ES. I had followed the instructions in the first manual when I first got my bike and ran the colder plugs. This caused the plugs to soot up very badly and sometimes 1 or 2 would foul when the engine was cold. Once it warmed up they would clear and it would run fine. Switching to the ND W22ES-U plugs solved the problem; I haven't had a fouled plug since switching. Ed