Motorcycle Repair: rejetting carbs, kawasaki vulcan 800, aftermarket pipes

Question
I have a 2004 Kawasaki Vulcan 800.  I replaced the factory exhaust with a custom 7/8 in. baffle less fishtail system.  I never re-jetted the carb.  I was told that if the inside of the pipes were black that it would be fine.  Is that true or should i re-jet the carb?  What should I jet it to?

Answer
Hi Daran...

I'm not sure why someone would tell you to check the color inside the pipe, as that is not an accurate way to determine if a re-jet is in order. First, let me state some facts: Installing aftermarket pipes does not ALWAYS require a rejetting. Even if a re-jet is in order, you may never completely eliminate all popping and gargling. Now with that stated... the first thing I would ask myself is "Does the bike run good and perform well?". That is the first indicator. Then I would read the spark plugs and see what is going on in the heart of the motor. We are looking to find out if the new exhaust system is causing your bike to run too lean... which is VERY bad for it. I would start by cleaning the spark plugs, then ride the bike for like 10 minutes under normal conditions (just to warm it up) and when you are almost at the end of that warm up ride, hit the throttle full for a short distance. While you are still at full throttle, turn the run switch off while simultaneously pulling in the clutch and coast the bike into your driveway or garage. Do not restart it until after you have read the plugs!!! Pull the spark plugs and look at them. Ideally, they should be a light tannish (or gray) color. If so, all is well and no re-jet is necessary. If they are black and sooty, then the bike is running too rich. If the insulator tip is white with dark or black specks on it, or blistered... then you are running too lean and you should re-jet. If you need to re-jet, the best way is to go one size at a time and test ride the bike each time until you find the best jet size. You will only need to re-jet the main jet and you'll prolly need to increase the size... BUT... only if the spark plugs indicate the engine is running lean. Unfortunately, I don't know what brand and length pipe you are using, but 7/8" is pretty skinny, so the new pipes may actually be producing a back pressure that is suitable for your engine and a re-jet will not be needed. In summary... if the bike runs good, performs well and the plugs read ok... then no worries!! Hope this helps ya Daran!!!

Thanks...
Jack