80cc bike really slow

SoldierBoy

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Feb 5, 2014
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Ok i had a 80cc bike kit awhile ago and there not slow they do 30-35 mph and this one that i ahve does 15 and takes forever ive cleaned the carb twice and still no change i can turn the idle screw all the way in or out and it does not do anything . ive also messed with the throttle cable to set the idle speed using it but ugh its not working right .
 

donphantasmo

Member
Oct 3, 2010
372
8
18
Middleburg, FL
I would change the fuel, make sure the oil mixture is right, change the spark plug. Also, check the gearing, as well. Start with the fuel, oil and spark plug. And go from there.
 

crassius

Well-Known Member
Sep 30, 2012
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many sellers are offering cheap kits now that may be older than the most recent kits

some have un-balanced cranks and some have polished cylinders

these motors may take between 60 and 100 miles to run in enough to develop full power - often, the carbs on these are very rich also, so that dropping the needle to a leaner position can help a little on hills
 

GoreWound

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Dec 1, 2014
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gearing is a big issue, you only have one so dialing it to where you need it is important.
my bike is heavy, and I have a lot of hills so my bike is slow. That's that.

also if the engine isn't broken all the way in yet almost half of your potential power could be missing. my two stroke was super disappointing to me until the day I was riding it and it made a sputtering noise slightly like two stroking for a few minutes, I seemed to be getting more power during the sputtering, so I tried giving her some gas to see what would happen. this was the moment the engine completed it's break in cycle, the "sputtering" was the engine occasionally getting good compression and ignition. banging the gas seated the piston rings properly, combined with the warmed cylinder and few months of letting it wear in beforehand, I immediately got about twenty percent more power across the RPM band.

but if you live somewhere flat you can always swap out the rear wheel sprocket with a smaller diameter one.

think about driving a manual car, if you leave it in first the car takes of great and tops out at about ten KPH.
if you try and start from stopped with the car in fourth gear you may not even be able to make it take off, but you will maintain whatever terrible acceleration you have until the cars top speed.
 

SoldierBoy

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Feb 5, 2014
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The motorized bike is not heavy its a aluminum Bridgestone CB2 (Vintage race bike ) the gearing is like any other gearing its the stock pieces they give you in the kit generally all the same .I did find somthing though the gasket from the carb mainfold to the motor is old and very bad .So its time to cut my own out of gasket material
 

Agreen

Member
Feb 10, 2013
792
11
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Southeastern GA
A lean condition, caused by a bad intake seal, will cause a loss of power and bogging.

You need to read the spark plug to get a good idea of why it's so slow. Chalky white or no color means it's too lean. Wet or black means it's too rich. Brown means a good mixture.

Search for "plug chop". It's the process by which people tune carbureted engines (at least those that don't use a wide band O2 sensor). The process has been around for years, so there's a plethora of knowledge on the subject.

And also:
Replace the head nuts with shoulder nuts
Check the head nut torque
Replace the spark plug boot (you can find a good one at sickbikeparts.com)
Change the spark plug to an NGK b5hs (auto parts store)
 

SoldierBoy

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Feb 5, 2014
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Now the bikes doing somthing different its running full idle when i put my hand over the intake it keeps going its g3etting air from somewhere else .I found my intake manifold has a crack in it and my hand made seal sucks lol
 

Agreen

Member
Feb 10, 2013
792
11
18
Southeastern GA
The place where the carb and manifold meets. What a terrible design... Try an o ring in between the carb and manifold tube. It may work. Some resort to globbing silicone all over it. Try wrapping it in some tape to see if that fixes it, but don't expect it to last long. Just as a trial.
 

GoreWound

New Member
Dec 1, 2014
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boom fixed now to solve why my mileage sucks
mileage is one of the first things to get better at the engine breaks in.
also once you are broken in you can switch to a less oily gas mix which will further increase your mileage.

also these little engines run much better when warmed up, so if you get into the habit of starting it up then letting the engine idle for a few minutes before you get riding you will immediately notice an increase in mileage.
 

2door

Moderator
Staff member
Sep 15, 2008
16,326
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Littleton, Colorado
Depends. If you rode it like an elderly lady, maybe not. If you were a little hard on it occasionally, ran it at WOT and made the engine work a little, it should be close.

There is a lot of discussion here on 'break-in procedures', What works, what doesn't. Take a look through our 'search', type in 'Break in' and set back for an evening's worth of reading on the subject.

Ask any professional tree trimmer how he 'breaks-in' his chain saws. My guess is you'll find few who say they run it at partial throttle, over lubricate it and treat it softly. Most will tell you they take it out of the box and put it to work. Apply the same logic to your 2stroke bicycle engine and it, and you will be happier.

You'll get differing opinions. Mine is just one.

Tom
 

Davezilla

New Member
Mar 15, 2014
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San Antonio Texas
I gotta agree on the break in... best way to break these in is to mix up a batch of 32:1 using dino oil and ride it like ya stole it, the only exception is to keep the trips short so the engine cant overheat...
 

SoldierBoy

New Member
Feb 5, 2014
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United States
yea i have been riding it crazy it seems to get a little faster but its very slow doing like 15 i can keep up running with it and crappy 15 mpg.Yes thats per gallon not per container its getting better slowly very slowly