KZ200A bogging at highway speeds (50+ MPH).

The bike is a 78 KZ200A. I bought the bike not running so it has been a project. the bike has 3800 miles on it so its in good condition. Things I have done in maintenance to get the bike in running condition. Cleaned and rebuilt carburetor, Adjusted points and cleaned, new spark plug, new carb rubber boots, cleaned and sealed rusty gas tank and replaced petcock, adjusted timing and ignition timing, oil change, replaced battery, replaced coil pack, replaced rectifier. I am sure there is more that I have done to it I just cant think of it at this time.

The issue I am having with the bike is that it runs good at lower speeds (anything under 50mph) for any duration of time. Once I get up to 50 mph and maintain speed for a mile or two the bike ends up bogging and dying. The bike will start back up again once it has been shut down. I have checked to see if it is a vacuum issue with the gas tank by running with the gas cap open and had no change in the symptom.

Thank you for any help.

dragonov_elite wrote: The bike is a 78 KZ200A. I bought the bike not running so it has been a project. the bike has 3800 miles on it so its in good condition. Things I have done in maintenance to get the bike in running condition. Cleaned and rebuilt carburetor, Adjusted points and cleaned, new spark plug, new carb rubber boots, cleaned and sealed rusty gas tank and replaced petcock, adjusted timing and ignition timing, oil change, replaced battery, replaced coil pack, replaced rectifier. I am sure there is more that I have done to it I just cant think of it at this time.

The issue I am having with the bike is that it runs good at lower speeds (anything under 50mph) for any duration of time. Once I get up to 50 mph and maintain speed for a mile or two the bike ends up bogging and dying. The bike will start back up again once it has been shut down. I have checked to see if it is a vacuum issue with the gas tank by running with the gas cap open and had no change in the symptom.

Thank you for any help.

Check to ensure there are no kinks or obstructions in the fuel line. They can create a condition where the fuel flow from the tank to the carb is not keeping up with the rate of fuel consumption by the engine. If this happens, the bike will act like it is out of fuel, but after it sits for a short time the carb will be replenished and the engine will run again. At low speeds this problem may not show up if the engine is using fuel at a slower rate, but when the fuel demand is greater at high speeds the problem can occur. Guess how I know? :laugh: Ed

Cool, ill look into that tomorrow. Could an inline fuel filter possibly cause a choke point on this carb?

Thanks for the reply.

It depends on which inline filter you have. Some reduce the flow if the fuel system (like that of our KZ bikes) is not pressurized. Other filters don't reduce the flow much at all. If you cannot find any problems in the fuel line itself you may want to bypass the filter and make a 50+ mph run to see if the problem persists. If it does you should get a different inline filter. I use a Golan Super Mini Fuel Filter. It was relatively expensive, but I will never need to replace it, and it doesn't restrict the flow of fuel. Ed

I didn't see where you said you adjusted the valves. Have you? If not they should be done.
Steve

Im with Ed on this .
Is fuel line original ??? They swell up internally over time .
Fuel petcock clean of debris . Is petcock vacumn actuated ?? Just because you cleaned the tank never assume anything
Test fuel system by disconnecting at carb and let fuel pour into a can and check for good solid stream of gas
Next if all else fails pull carb back apart and check for debris and or water in bowl
Dave

You can confirm the fuel supply issue by turning off the gas once the bike stalls, drain float bowl and compare amount to havingbthe fuel,on and just sitting for a few minutes. Recheck float measurement too.

Well i did find a kink in my fuel line. I replaced that so that there would be no more kink. Still had issues. Finally replace full lines and tried running with out a fuel filter. Issue is still present as of now. Thank you for the suggestions. I will be checking my float level and fuel flow out of the petcock. Once i run the tank down low enough ill pull the petcock out and check for debris. The petcock i have on the tank now does have a filter built onto it. ill also be double checking my valve clearances and ignition timing again. Now its just finding time to do it all hahaha.

Yes you have to begin with the in tank petcock filter.
I have seen a lot of tanks with rusty debris filters and fuel level sending sensors.
Water is heavier than fuel and is hidden in the lowest sector of the tank and do a destroying slow and continuously work.

Well I got the issue figured out. Ended up being the position of the floot position. Thank you for your time and input guys. The tank and petcock checked out good.