Loss of power no solution

ElCangrejoPR

New Member
Joined
Apr 8, 2018
Messages
7
Hello forum. Upon doing a LOT of research I decided to open an account and ask for help. I got an 80cc bicycle engine off ebay with NT carb. It already did break in period, around 4 to 5 tanks. Mixture was 16:1 then we increased to 20:1 then around 30:1. The bike has a massive power loss. It runs top speed 15mph with luck and going uphill is more an assisted peddaling.
Things I have tried to increase power:
-moved the c clip for the needle (moving a notch up from center helped a bit)
-checked float and adjusted jet which was loose,( no change here.)
-changed fuel line which leaked and filter (no change to performance)
-changed spark plug (no change)
-checked muffler to see if it was clogged and it wasnt.
-removed muffler cap (increased power a bit but still slow to build up speed)
-tried different nt carb (no change to perf.)
-tried an HP carb (made it loose performance)
-checked and adjusted clutch
-checked magneto and voltage for magneto and cdi
-changed cdi (original one was giving a reading of 7 instead of the one it should have, changing cdi improved performance a little bit)
-adjusted every screw and cap for any possible leak and nothing.
The only thing that seemed to boost the power was removing the muffler cap and rising the c clip a notch to make it leaner. Was have 2 more bikes and one of them runs flawlessly. Has good power and goes fast. We keep switching parts between the 2 and nothing seems to improve the performance of the engine. We opened up the engine and looks fine. We do notice the engine only responds fairly to the throttle when it goes from 0 to 3/4. At full throttle if its running it looses power and decreases speed ubless taking it to full throttle very slow. Also not even at half throttle the bike has enough power to sustain speed if it goes a little bit uphill. Any advice?
 


crassius

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Joined
Jul 23, 2012
Messages
4,575
what size rear sprocket do you have? seen similar on 38mm stroke motors with 36T sprockets
 

crassius

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Joined
Jul 23, 2012
Messages
4,575
I'd first try doing a cold compression test, but you may also want to loosen the muffler about 1/8 inch to see if it may have gotten blocked by something
 

ElCangrejoPR

New Member
Joined
Apr 8, 2018
Messages
7
I'd first try doing a cold compression test, but you may also want to loosen the muffler about 1/8 inch to see if it may have gotten blocked by something
I will go this week to do a compression test. As for the muffler, without the cap it gains a little boost in power. Still needs pedal when going on a small hill. We put a camera through the inside of the muffler and its not blocked. Everything is clear. The union between the engine and muffler is also clear. Been tweaking it and it seems to be developing more speed only in flat surface and when accelerating slowly. If you throttle to full it looses power and rev.
 

FurryOnTheInside

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Joined
Sep 23, 2013
Messages
3,425
Havent spotted any leaks. Only leaks it had were some oil drops from muffler at the beginning of break in and fuel line was broken. About the frame mount I don't think its in a bad spot. All tight no movement.
If it "four strokes" when you go WOT, I would try it with the air filter box removed, but still with some type of filter.. or just drill holes in the box to let more air in. The stock air filter box is restrictive so that would richen the A/F ratio at higher RPM and WOT.
 
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