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Wayne S.
Wayne S., Motorcycle Mechanic
Category: Motorcycle
Satisfied Customers: 1255
Experience:  Experienced and Licensed Motorcycle Mechanic - all sizes and brands welcome.
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I installed a 50mm big bore lot on my 50cc taotao 2014

Customer Question

Hey I installed a 50mm big bore lot on my 50cc taotao 2014 scooter. Only has 80km on it. I ran perfectly like a charm before the big bore kit. After I installed the big bore kit, with the exhaust big valve head, Keihin carb the scooter has a REALY hard time turning over, it takes a much more former to turn the flywheel over now after the installation. Feels like there's too much compression. The electric starter doesn't have enough power to turn the engine a full revolution (fully charged new battery) but sometimes does spin it fast enough to get it going. I've started it once before using starting fluid then died on me after 30 seconds. My kickstarted broke after trying so many times which I ordered parts for and. Getting it fixed. People told me to add another base gasket to decrease compression. The engine turns so smoothly by hand and electric start when I unplug the spark plug.
Submitted: 1 year ago.
Category: Motorcycle
Customer: replied 1 year ago.
Force* instead of former
Expert:  Wayne S. replied 1 year ago.

The valve timing can affect the compression, double check that and make sure spark plug is not too long.


Customer: replied 1 year ago.
Before I installed everything I made sure everything was ok top dead center and made sure it still was while I was putting the cam shaft on with the timing chain.
Expert:  Wayne S. replied 1 year ago.
If your engine is turning over smoothly with the plug out then
maybe the compression is just very high. This is a bit odd as
usually compression is not altered by very much.
Is the carb flooding the engine with fuel as this could create
a hydro lock with too much liquid in the cylinder.
Added base gaskets may help unless you got some kind of high compression piston. Make sure it is not getting to much fuel or oil in the cylinder.
Customer: replied 1 year ago.
With the spark plug in I can spin the flywheel one full rev then after that rev it takes a lot of force to get the flywheel to its next position then normal again.
Expert:  Wayne S. replied 1 year ago.
There will be some resistance due to compression but are the valves
clearance set properly while engine is on the compression stroke
and the "T" mark aligned on the flywheel? About .003" should be
Can you tell if the piston is hitting on something?
Are the valves opening and closing normally when you look at the rocker
arms moving. Spark plug is not too long is it?
Was the head gasket the correct one for the larger bore size?
Customer: replied 1 year ago.
I could tell that The piston isn't hitting anything, timing chain is all adjusted with the T on the flywheel and the 2 wholes alighed with the head and the top hole on top. The gasket came with the big bore kit and fit perfect. Spark park is the right size. I tried Turing the flywheel while I was screwing in the spark plug and herd a hissing sound which is normal because of the compression leaking through the spark plug while it wasn't right so I know for sure I have compression but once the spark plug is snug it get hard to spin the flywheel after each full rev. It gets hard when to spin then that timing magnet on the flywheel is passing the sensor then after it gets in that position is gets back to normal. Even when I electric start it it spins fine then slows down when trying to turn on the hard part then gets back to normal. I know I'm getting gas as when I try to turn it over the spark plug has fuel.
Expert:  Wayne S. replied 1 year ago.
Your engine sounds like it has compression so it should run if all is well otherwise. If the compression is too high for the starter to handle you will have to pull the cylinder and see if you can reduce the compression. Possibly you need a different piston.
If it will fire then check that your new carb is clean inside
and that the float needle is not stuck closed.
Once you have fuel and spark it should run even if it is reluctant at first. Many new carbs corrode during shipping and need to be totally
cleaned out with some carb cleaner.

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