QuestionI have a 93 Suzuki VX 800 that is stock except for an aftermarket exhaust.( slip on mufflers )I bought the bike 6 months ago with 8500 miles on it. It ran decent until recently when it has started to develop a surge at 70+ mph. If I add a little choke, it runs smoother. I pulled the plugs and they are tan in color. At idle the bike had a slight amount of black smoke when I blip the throttle. Since the problem was only at 5,000 rpm and higher, I pulled the carbs and raised the needles slightly, set the float levels to factory specs (Rear carb was incorrect) and then set the idle mixture to 1 3/4 turns out.(was 1 1/2) The engine is much more responsive, but the surge is still present.(P.S. I also checked the petcock fuel filter,replaced the air filters and checked the fuel cap vent-no problems there)Note: The surge isn't always there and under hard throttle it misses once in awhile. The bike has a vacuum operated fuel pump and I'm going to replace that next. If that doesn't work, what would you suggest?
AnswerHi Lynn,
I sugesst that you check cylinder compression, valve clearances, and carburetor synchronization. Adjust or repair accordingly.
Once the above are within service limits, install new spark plugs, inspect spark plug leads, and investigate current leaks and flash-over.
If the problems persists, consider inspecting jets for evidence of damages at the screw slots. Defects to jets caused by tool tips causes turbulance to fuel flowing over affected area. This may cause performance problems noticable at higher speeds.
Otherwise, search and destroy. Keep probing until you discover the source of the problem.
Respectfully,
Mark Shively
