sputtering and bogging when hot

I asked about this problem in the carb section some time ago but talking to a mechanic has led me to believe that this might be beter place to try to solve my problem . My 1976 kz750 B twin had been running great and I took it on a weekend trip last summer. it ran beautifully, on the last day of the trip we were stuck in some traffic close to home and it started to bog and sputter when at highway speed. I got home though and didnt use it for the rest of the season. This year I took it out and it ran great at first, but when it got hot it started to do the bogging and sputtering thing again. doesnt do it cold and for short trips runs like a charm. I thought it might be carbs since I changed the plugs and fuel but I talked to a mechanic I know and he thinks it might be points ??..anyone have any ideas ???

I would think check your coil. it sits right above the engine

Christo wrote:

I asked about this problem in the carb section some time ago but talking to a mechanic has led me to believe that this might be beter place to try to solve my problem . My 1976 kz750 B twin had been running great and I took it on a weekend trip last summer. it ran beautifully, on the last day of the trip we were stuck in some traffic close to home and it started to bog and sputter when at highway speed. I got home though and didnt use it for the rest of the season. This year I took it out and it ran great at first, but when it got hot it started to do the bogging and sputtering thing again. doesnt do it cold and for short trips runs like a charm. I thought it might be carbs since I changed the plugs and fuel but I talked to a mechanic I know and he thinks it might be points ??..anyone have any ideas ???

Of course I cannot diagnose you problem in one description, but *man* does your problem sound like the one I fought for over a year. Look at some of my old posts (here and in the archive), almost the same description...

...yep, it was my coil... new Dyna, no troubles....

bad points will have you thinking your bike is near death. check gap and timing. look for sparks at the points when running that is bad and is a sign to get new ones and condenser too.
next the standard compression test (W.O.T.)
you did the fuel and plugs. What you find will tell you what to do next

Let me ask you this then, is there an easy way to check my coil ?..is it as simple as checking the voltage at the coil ? will I need to run the bike till it's hot ? and will the voltage drop as the bike heats ??

Let me ask you this then, is there an easy way to check my coil ?..is it as simple as checking the voltage at the coil ? will I need to run the bike till it's hot ? and will the voltage drop as the bike heats ??

If you find your coil within specs when hot check your valve clearance. When was the last time it was checked?? My 77 kz650 was doing the same thing when it got hot.I pulled my hair out for some time and came to find the clearances were on the tight side of the scale. Good luck

Let me ask you this then, is there an easy way to check my coil ?..is it as simple as checking the voltage at the coil ? will I need to run the bike till it's hot ? and will the voltage drop as the bike heats ??

Might be a cracked coil shorting but sounds more like the valves need some clearance. They start tight and get tighter as the bike warms and you lose seal when they are shut, ruining compression. CHECK VALVE CLEARANCES...