81 Kz 305 Wont Rev Past 4000 Rpm

[ck76239]

Hi Guys,
I finally got my 81 Kz 305 running. When I bought it, the carbs were gummed up. I completly disassembled them, and dunked them in carb parts cleaner. I then verified with compressed air that the passage ways were clear.

Trouble is, now that it's running, I took it out for a ride, and it runs fine until it hits 4000 rpm's. After that it wont rev much higher, and sounds like it pops and stumbles. I drove it 6 miles in an attempt to clean it out, but that did nothing. If you take it out of gear, it will rev to almost 6000.

I pulled the plugs and they are sooted black from running rich, but not oil fouled...

I checked the coils out, thinking that maybe they are breaking down, but they are within the specs listed in the service manual.

Any suggestions?

THanks!

[hayward6]

Cleaning the carbs is not enough, its a good start but you need to verify the internal parts are in good shape and the floats are adjusted right. One of the big problems with using compressed air is that you run the risk of actually bending the tongs and throwing the floats out of adjustment. I would pull them back off and make sure the floats are right before doing anything else.

If its running good at low rpms then your pilot jet and screw should be fine, but if your starving for fuel at higher rpms you either have a blockage from the tank or the floats are wrong. and of course this is only if the problem is with the carbs good luck and let us know what you find.

[ck76239]

Thanks for the reply.

The compressed air never hit the floats, as I blew each individual jet out, and then the empty carb body. I will verify float height, but the condition of the plugs indicated that it running rich, and not starved for fuel.

I am thinking more and more it's an electrical problem, but I'm just not sure where to begin

[StarGate]

I would suspect it's more likely fuel related but it could be either. Does the bike had the factory exhaust and air filter setups or has either of these been modified? Are you running factory jets in the main and pilot? When you hit the 4k rmp mark while riding, did you try to turn the choke on and see if it gets better or worse? That would tell you if it's rich or lean at that point. If the plugs are black but not from burning oil then it's definately running rich at some point but that could be during low rpm and it could still be lean at high rpm if the main is too small. Just some thoughts to consider.

[ck76239]

I am running the factory exhaust and factory airbox. I'll play with the choke to see what effect is has on the bike's performance.

Thank You

[Andy the gringo]

It sounds like more of an electrical problem to me. Check your timing advancer to make sure it isn't stuck also verify that you are getting 12 volts at your coils. You may want to do Wired George's coil repowering mod.