couple of questions.

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oldpot

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Jun 21, 2012
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ok first time i took my 49cc out(4 years old engine got it off bloke on Craigslist)since i got it 3 weeks back for a quick run about 6 miles

first question, i got a single speed bike in what ratio to a 7 speed bike is the single speed gear, (1-7) feels like 5-6 on my bike, i am wonder if it because the Chain Tensioner is on the normal bike chain side (no idea why the bloke put it there ) but i know there's a 1/2 link on the sprocket chain side , from a standing start its hard to pedal to get the bike going i have no idea how i start on a small hill ,and i do have 2 small hills with traffic lights at top of them on a few places i will be going with bike ,, i wonder if i could take the Chain Tensioner off and shorten the chain and have no Tensioner on at all would ease the pedaling .pic of Chain Tensioner.

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2nd, when engine starts up to 5-10 mph , it jumpy and not smooth then from 10-20mph feels ok , but when i try put it bit more power it takes about 1-2 seconds before it goes forward and sometimes like that at 5-10 mph to when i go faster ,i struggle to get to 25mph (hope that 49cc would be ok at 25mph),
i am running a bit of old fuel that was left in tank with some 50/1 mix and this engine has only done 200miles in 4 years and i put on about 8 miles since i got it .any ideas?
 
2door

2door

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The tensioner on the pedal side really doesn't add that much resistance. But it is in the wrong place for a coaster brake bike. When you pedal backwards to apply the brake the bottom chain run takes all the stress of braking. If that tensioner slips or comes loose you might loose the brakes. Relocate it to the top chain run.

As for the engine being "jerky" at low speeds, that's normal if your speed drops below about 10mph. When moving that slow you need to disengage the clutch and pedal instead of using the engine. Starting an engine uphill is always a problem. Unless you have a multi-speed bike with a very low gear pedaling to start uphill will require some effort. Sorry, that's just the nature of the beast.
It appears from your photo that the rear sprocket is large. What size (tooth count) is it? The larger the sprocket the easier the bike will climb hills under engine power but it will also keep your top speed lower than a small rear sprocket. My guess is that sprocket is maybe a 48T, maybe larger. A little large for general purpose riding. a 40 to 44T are good all round sprocket sizes unless you're towing or climbing steep hills or going for top speed.

I'd run out that old fuel and mix up a fresh batch. You didn't say what oil you're using but 50:1 is a little oil lean unless the oil is formulated to run at that ratio. Standard 2 stroke oil should be up in the 32 to 40:1 ratio to provide proper lubrication. Some oils, especially the synthetics and semi-synthetics can be used safely at 50:1 but you need to read the label of the oil container to be sure.

Mix your fuel in a seperate container, never the bike fuel tank. Shake well before filling the tank. 2 stroke mix has a relatively short 'shelf life' and will loose potentancy after a while in storage. That might account for your rough running engine but we'll need to know more information to provide specific advice. What carburetor? What spark plug? Plug gap? etc.
Hope some of this is helpful.

Tom
 
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oldpot

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Jun 21, 2012
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ty 2 door for the info i will check what you ask for tomorrow if i can as i lied up with sprained back at the moment ,but hope i can get to check few things like sprocket size etc , the bike as a drum brake on the back , i not changed nothing on the bike since i got it as it looked ok, here a pic of it

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i have got Lucas 2 stroke oil ,again if i can cruise at 20-25 i will be happy i was doing 18-20 when i was on the bike and was cruising and still going 18 up a hill i been to get to garden so was pleased with that ,my big problem is if i have to stop the other hills that got triffic lights at the top might as well get off and walk across the crossing as no way i be able to start pedaling in traffic as well i was lucky was at green when i went passed last time hehe .
 
WightBoy

WightBoy

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Aug 30, 2012
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Check the local bike shop and see if they have a smaller sprocket for the front of the pedal side or a larger one for the back. This would make it easier to take off on a hill. Unfortunately, just having a single speed pedal drive, you can only do so much. With that brake, you can leave the tensioner on the bottom too.
 
maniac57

maniac57

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Oct 8, 2011
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I would swap out the front sprocket for a smaller one. Many single speed bikes are overgeared for our use and benefit from lower gears. I just built a fixed gear bike that had the same problem. They are geared for fast speeds rather than easy take-off.
 
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oldpot

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Jun 21, 2012
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ok a few bits of info , the back sprocket with the drum brake is 44 and the normal front sprocket is also 44, plug gap is 0.25 , plug is (ZBC,LB)the plug looked browny colour with bits on it , could be same plug he had on for 4 years but with 400miles could be ok , but i changed it to new one (same as the one i took out )i found in a bag that was in the back rack bag,
looks like the back wheel not the one that came with the bike as its no coaster brake on it ,and does look different to the front one looks , looks like he had a wheel made up , problem i found that when i turn the pedals a 1/4 of every turn it feels harder to turn the pedal and i can hear a scraping noise from back wheel somewhere but cannot find where it coming from i pinpointed where its making a noise but see nothing catching etcetc,(only if coming from the inside of the drum brake )but will have make bike hard to pedal??.

so what size front sprocket should i get and will it make it easier to pedal (say 3,4) on the 7 speed ratio scale ??as now feels like 5-6.

so whiteboy , the tensioner will not make it hard to pedal ??? off or on ?

and will i have to take links out of chain if get smaller front sprocket.?

ty again everyone for your info :).
 
WightBoy

WightBoy

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The brake/hub you have on the rear looks like one of the grubee hd hubs with a band brake. It works by having the band clamp around an inner hub. You may try to loosen the rear brake slightly and see if that works to make the noise go away. You really do not (in my opinion) need the tensioner on the pedal side and yes you will have to remove links to run a smaller sprocket up front. I cant really tell you how small of a sprocket to get without first knowing your current tooth count for front and rear. However, a few teeth can make a huge difference.
 
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oldpot

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Jun 21, 2012
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the front one is 44 you need to size of the rear sprocket on the normal chain side??

i just found out the (Z8C,LB)plug is the one came with bike kit from china so i ordered a better one , i will try find out what wheel it is but bending down kills me at the moment hehe , and find the rear sprocket size as well .
 
WightBoy

WightBoy

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Here is the website if you need info for the rear brake/hub that I think you have. http://www.grubeeinc.com/USA/HD Rear Axel kit.htm

Here is a website for calculating out gear ratios for your pedal side.
http://www.bikeschool.com/tools/gear-calculator

Here is a link to read up on what a "gear inch" is.
http://en.wikipedia.org/wiki/Gear_inches

In simple terms, the lower your "gear inch" number is, the lower your top speed will be but the easier it will be for you to pedal.

Assuming you have a 44 tooth front and a 16 tooth rear with a 26" rear wheel, it will feel like you have a 72 inch rear tire, 40 tooth front will be like 65" tire and 36 tooth will be like 58" tire.
 
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oldpot

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Jun 21, 2012
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i check rear and is a 18 t so that means with the chart is 64 inch but whats that in terms like a 1-7 speed ratio gear (eg could it be 4 or 5 th gear i am getting a little bit of drag as well when i pedal but i see how it goes and then if still dont like how it is i might change front sprocket, yes wightboy looks like the set up for back wheel the 2nd kit one looks like he got all the wheel if so the 150 i payed for it means better bargin for me:) ,
 
WightBoy

WightBoy

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well, in terms of 1-7, I couldn't tell you. On my 8 speed though, my 5 gear is a 17 tooth, so you are geared pretty tall. If you can go down to a 36 up front, that should make it like a 3rd gear roughly
 
Hoofbeats64

Hoofbeats64

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Aug 29, 2017
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While my bike was grounded, I made a silly mistake of hanging it in the garage. I think the way I hung it may have made the spark plug dirty? Hmmm, I wiped it off, what plug at the store (say going to Menards/Hardware store) do these 49 cc engines take? Lots to choose from... The chain seems jumpy, just wondering if that could be plug related... I had also put on the header exhaust port. Sounds deeper and the engine idles way lower. Adjust carburetor?
 
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