Modern Buddy

I installed a Prima exhaust on my Genuine Buddy 125 back in September and jetted up from no 92.5 to no 95.
Scoot ran great for a few months. Lately, I developed a flat spot in the mid-range during acceleration up to highway speed. Its irritating.
Pics of my plug reading from today are attached. One side of the plug looks a little lean (white) and the other side looks rich (darker than tan).
Should I return to stock jetting or maybe do something with the pilot jet?

The easy answer is to go to the next main jet size. However, it may be good to rule out other causes first. You might try to clean out the carb jets first perhaps.

Is there any weakness at part throttle?

Hmm, changing the main jet size should not have much affect on the midrange because it only controls the fuel mixture at 3/4 to full throttle. What you should try is raising the needle valve a little to richen up the midrange. Since the carbs used in our scooters do not have adjustable needle valves, the easiest way to raise it is to put a thin flat washer (1mm thick or less) under the existing c-clip that is on the needle jet. The difficult part about this is finding flat washers with a small enough hole and are thin. Try looking for them at a hobby shop that sells RC (radio control) models. If that fails, you can find them online from Tower Hobbies.

If it's not too much for you I would first clean the jets then I would try some seafoam for a few tanks. You could also try just adding seafoam for a few tanks first. Looks like the idle jet may be partially plugged. If so there is probably some other varnish covering carb parts.

I will try the Seafoam first.
I moved to the coast at the end of last year and that seems to coincide with the mid-range problem.
We still take hour long rides, but we ride on the beach, where the speed limit is 20 mph. We rarely take a long ride at cruising speed anymore.

wheelbender6 wrote:I will try the Seafoam first.
I moved to the coast at the end of last year and that seems to coincide with the mid-range problem.
We still take hour long rides, but we ride on the beach, where the speed limit is 20 mph. We rarely take a long ride at cruising speed anymore.

Was there much of an altitude change? This could affect the carburation mixture. Or, it could just be gummy bears in the carb like BuddyRaton said.

Elevation only changed 100 ft or so. Good idea though.

babblefish wrote:Hmm, changing the main jet size should not have much affect on the midrange because it only controls the fuel mixture at 3/4 to full throttle. What you should try is raising the needle valve a little to richen up the midrange. Since the carbs used in our scooters do not have adjustable needle valves, the easiest way to raise it is to put a thin flat washer (1mm thick or less) under the existing c-clip that is on the needle jet. The difficult part about this is finding flat washers with a small enough hole and are thin. Try looking for them at a hobby shop that sells RC (radio control) models. If that fails, you can find them online from Tower Hobbies.

I think you may have throttle position and rpm range confused here. Mid-range refers to the middle section of the RPM range that the motor is capable of, not half-throttle. You can be at full throttle and pass through the mid-range of the power band depending on how the variator is set up.

It refers to both. When accelerating to cruising speed, the power seems to drop off approaching 40 mph and pick up again after 45 mph. The flat spot is even moRe noticeable if I use much more than 50% throttle.

Check your variator surface. Is there any varnish or grooving affecting the belt movement?

The Seaform appears to have taken care of the problem. I'm glad I didn't pull the carb apart before trying it.