Flat spot in midrange
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- wheelbender6
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Flat spot in midrange
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?
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?
2013 Buddy 125, Prima Pipe, #95 main jet, Orange CDI
- babblefish
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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.
Some people can break a crowbar in a sandbox.
- BuddyRaton
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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.
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'06 Cream Buddy 125, 11 Blur 220, 13 BMW C 650 GT, 68 Vespa SS180, 64 Vespa GS MK II, 65 Lambretta TV 175, 67 Vespa GT, 64 Vespa 150 VBB 64 Vespa GL
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'06 Cream Buddy 125, 11 Blur 220, 13 BMW C 650 GT, 68 Vespa SS180, 64 Vespa GS MK II, 65 Lambretta TV 175, 67 Vespa GT, 64 Vespa 150 VBB 64 Vespa GL
- wheelbender6
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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.
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.
2013 Buddy 125, Prima Pipe, #95 main jet, Orange CDI
- babblefish
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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.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.
Some people can break a crowbar in a sandbox.
- wheelbender6
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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.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.
- wheelbender6
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- wheelbender6
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- Posts: 852
- Joined: Sun Jul 07, 2013 1:27 am
- Location: Houston area