Motorcycle Repair: hesitation/throttle, spark plug gap, air fuel ratio

Question
Hi,

I have a 1984 Honda Shadow VT700. The bike has a hard time getting past 80
mph. If I crack it wide open the bike start's breaking up, but if I start to back
off the throttle slowly, the bike will pick back up and ride smooth. If I listen
to the pipe's while it break's up, the left side sounds nice and steady.
However,
the right side cut's in and out rapidly. I completely cleaned both carb's and
jet's spotless! I replaced the fuel line's and fuel filter. I also replaced the pilot
screw's and have them at the stock 1 1/4 turn out. Fuel and spark is good.
Lastly, the hesitation doesn't happen in neutral, it only happen's when there
is a load on the motor. I am stumped.

Any suggestion's would be greatly appreciated. Thank's.

Mike  

Answer
If it's a severe miss, I'd be looking for a spark leak, either in the coil or plug wires.  If its a rather soft miss it could still be an air fuel ratio problem.  Take the bike out and get it to miss for a few minutes and hit the kill switch and allow the bike to coast to a stop.  Pull the plugs and check the color of the electrodes.  If they are very white, it could be a float level problem or an air leak somewhere.  Given it only happen at high load, I'm betting it's not an air leak but it still could be a float level issue.  

My money is on the spark leak.  As the pressure in the cylinder increases with load it take more voltage to get the spark to jump the spark plug gap.  A sure sign of this type of problem is a miss under load.  I'd bet you don't have to be going 80 mph to make it miss.  If it's a spark problem, find a hill and put it in 3-5 gear at a fairly low speed and open the throttle up to increase the cylinder pressure.  It should start missing as soon as it's under a heavy load.

It could also be a plug gap that is too wide or a partially fouled plug.  If the voltage required to jump the plug gap is too high, it will find another path to ground.  It can jump across the plug wires, inside the plug boot, inside the coils or down inside the plug where you can't see it.  

I'd be curious what you find.      

Regards,
Rich