Hello! So as i have a summer job now i am taking my bikes to work everyday (ironically i work at a bike shop as a mechanic). Anyway a few days ago i tested out my broken in YD100 bike that i made for towing a trailer and put back on my "custom" pocket bike exhaust. Thing is that it has a higher top speed at about 3/4 throttle. I reached 60km/h on a flat. If i try to pull with full throttle it starts 4 stroking like crazy at about 35km/h then if i let of the throttle it pulls and sounds very nice. If i pull the spark plug it is black so this means i am running rich... If i use the stock exhaust it performs good at WOT but it only reaches about 40km/h. Would i solve this by using a smaller jet size? (i will open up the carb and see what size is in it right now). I use the bike at about 350m and the ambient temp of about 20-35 degrees.
Exhaust Top speed and jet size
- Thread starter MinimumVK
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Sidewinder Jerry
Well-Known Member
What size tires are you using and what size rear sprocket are you using?
GW's Motorized
Well-Known Member
You should clean or replace the plug, go for a ride and make sure there is no 4 stroking, then check the plug burn.
I am on 26x2.00 knobby tires and a 44t sprocket at the rear. Thought about going to a 36 tooth sprocket but even now it barely pulls up a 15 percent incline... (i live in a hilly area) Smaller hills it does really well without pedal assist even with the stock exhaust. A few days ago i was pulling a trailer and some car parts (about 30kg all together) and i did need pedal assist on most hills (lets say 10 percent)
GW's Motorized
Well-Known Member
I've thought about getting a phantom and running a 60t just to see what happens.
Sidewinder Jerry
Well-Known Member
If you were doing 60 kph on 26" wheels using a 44t sprocket that means your engine was turning 8695 rpm at 3/4 throttle. Without engine modifications these engines might at best reach 8000 rpm at full throttle under a light load. Was the 60 kph a down hill speed???.
Doing 40 kph on 26" wheels using a 44t means your engine was doing 5796 rpm. Around 6000 rpm at full throttle is what the stock engines normally do on level ground. Could it be you came down a hill got up to 60 kph at 3/4 throttle; then slowed to 40 kph at full throttle on level ground????
Maybe it was a little incline but at full throttle it definitely does not want to go. I can tell you the engine was really screaming when going 60
It will pop a wheelie like you wouldn't believe and leave your sorry little butt wiping the pavement in place of toilet paper...lol.
Look at what happened to this guy in the first 1.00 minute of riding it after the fast forward building of it...lol...lol...He was only using either the 44 or 48 sprocket with his...lol.
GW's Motorized
Well-Known Member
Looks like that hurt, especially on gravel. Yup, definitely throwing that idea in the scrap bin 
