Trying to figure out why my kymco 150 is bogging down...
Any insight?
Lou
I heard the miss of the motor when you blipped the throttle. Most likely the pilot jet circuit is clogged. Clearly you have a condition of lean misfire or skipping. This happens when you open the throttle off idle and there is not enough fuel supplied by the pilot jet or "slow jet" and so the motor is getting more air but only the same amount of gas suppled at idle. Once you pass 1/4" of twist (excluding the removal of the initial cable slack in the throttle which does not count) then you get into the larger "main jet" which does not clog as often simple because it is a much larger "pipe" and the main jet has a main jet needle that regulates gas flow but also serves to poke a hole in the jet if it gets clogged.
Why not a vacuum leak? You could have a vacuum leak but it would effect the idle (irregular) and the entire range of throttle - although a small vacuum leak would be more noticeable at low speeds, rpms etc. Also, vacuum leaks are fairly rare - most scooters here are less than 10 years old, rubber has not had time to crack, miles ridden are very low - less than 10K and modern motors make extensive use of electronic sensors which vastly reduces the number of vacuum hoses and thus the potential for vacuum leaks. Old motorcycles I worked on from the 80's with an inline 4 cylinder had quite a few vacuum hose, same with cars - like spaghetti. The Grandvista and other similar models use a throttle position sensor no vacuum to advance the timing (spark advance).
Use seafoam or a related carb or fuel injection cleaner at a higher concentration level. If that fails do a visual inspection by accessing the the area around the carb to look for possible vacuum leaks. If that fails, it is time to remove the carb and clean it on the bench. If you do the last item take lots of digital pics at every step and
DO NOT REMOVE THE TWO SCREWS ON THE TOP OF THE CARB (the "hat" where the diaphragm is - the diaphragm is easily damaged and costs about $35 to replace!!) and there is NO reason to open that area as there is nothing to clean.
If the carb is clogged how did this happen? Scooter sits for a year or much more with old un-stabilized gas like my 2005 Kymco GV250. After a year or two it was parked at 1600 miles and sat for around 5 years. It was purchased and take to the dealer. They did a so so job of cleaning and said if that is not good enough replace the carb $350 for a new oem carb (aftermarket carbs can be used ~$50 but an adapter must be made for the electronic TPS to attach to the carb).
Short story long... I'm in the exact same boat as you. I cleaned my carb twice, accidentally took of the part I said not to and my scoot would not go over 45 mph! Took it apart and got it right and make things much better but I still have the hesitation the same as you have. Bought and after market carb from the same mfg Keihin CVK but aftermarket car makers sell carbs that assume your motor uses a vacuum hose for spark advance rather then the electronic TPS that Kymco uses - and virtually all modern cars starting in the late 1980's. I saw a post online where a guy did a DIY adpter on his aftermarket carb to fit the TPS and I'm considering doing the same when I have time.
Before doing this the last part to check / clean is the idle mixture screw which affects 0 to 1/4 inch of twist of throttle. I will remove the screw (counting the turns) shoot carb cleaner and stick a bristle from a wire brush in there then compress air and reassemble and test.
Final Chapter:
Any condition that results in lean burn (too little gas) regardless of the reason - clogged jets, vacuum leak or gasp both problems... cause the engine to run too hot and slowly burns it up. So the little issue of a sitting vehicle where the owner lets it sit and does not add a $5 can of fuel stablizer or drain the fuel before storing it results in annoying and expensive performance issues later on and potentially a lean burn that harms the motor.
