Motorcycle Repair: Aerodynamics and Carbs, stock airbox, mixture settings

Question
Hi I have a problem that has me stumped! I've made 1 good '86 zx100 out of 2 parts bikes. I know it's a tad lean and i need to sync the carbs. My problem is when cruising at @ 70mph(1/4 throttle) the revs fluctuate and if I whack the gas it stumbles then goes great= Lean, if I lay over the tank and improve the aerodynamics the surging pretty much goes away and when I hammer it the stumble is hardly noticeable. The carbs are clean(3 times). Stock airbox and 4-1 yosh. I have a new K&N Jet Kit on the way. Thanks Mike

Answer
Hi Mike.

Before this problem can be properly assessed, you need to do the service on the bike.  Clean and synchro the carbs, do the valves and timing, and make sure that the oil, oil filter and air filter are all good.

As far as the bike running lean, it could be due to air leaks in the manifolds, so make sure that the manifolds aren't leaking, which could cause the problems that you are describing, such as the flutter and running lean.

Do all of that before you go changing the mixture settings or the jets.

Good luck and ride safe.
FALCON