rebiuld top end

GoldenMotor.com

Kioshk

Active Member
Oct 21, 2012
1,152
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Connecticut
Make sure you've properly lapped the head and cylinder and torqued the head down adequately. It sounds like you MIGHT have low compression. Of course this will increase as the new parts break-in.
 

Bobbyz

New Member
Jul 15, 2014
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56
reading pa
iam new to this dont know what you mean the bike will not even move runs when starting good just dont revand no power
 

BobbyT

Member
Mar 16, 2014
162
15
18
Santa Maria ca.
What engine is it? Did you use a torque wrench to tighten the nuts?
Did you line up the rings with the keepers in the grooves.

Do you have a compression tester and a torque wrench?

You should let us know as much info as possible when trying to get help. It will help us help you. The Google search near the top of the page can be very helpful to find threads for how to do almost any repair.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
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USA
if you're sure the carb is actually opening without giving more revs, then I'd run it a bit to see if oil seeps out somewhere (indicating a compression leak)
 

Bobbyz

New Member
Jul 15, 2014
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reading pa
It a 80/66cc china girl put a new top end new cylinder piston rings and head with new gaskets but very thing to specs I got off sight motor runs good till you give it gas to go it sound like it getting chocked the chock off motor leve it idle it runs good let it run don't see any ooil leaking any place
 
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crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
I'd first buy & rent a compression gauge for a quick check (some auto parts stores loan tools for free). I'd next (should have been done before the start) check the depth of the ports between the new barrel & the old to see if there are diffs there. You may need to go thicker/thinner with base & head gaskets.
 

Bobbyz

New Member
Jul 15, 2014
48
0
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56
reading pa
I have a china girl 80 cc I put a new cycleder piston and rings as a new CSI and mag coil motor starts runs great give it gas nothing stays running but don't rev there no oil leaking any place took it to small engine shop compresh he says good for the size of motor what else could it be :-||
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
one quick check is to loosen the muffler just a bit and see if it revs then

an easy mistake could be putting base gasket on wrong, which can block transfer ports

most common mistake is to order a top end set that has diff barrel height, diff port height, or diff piston - if you find no other reason, then take it off & carefully measure all between old set & new

that, and debris falling into bottom end are some reasons I rarely rebuild top ends when new motors are so cheap
 

Bobbyz

New Member
Jul 15, 2014
48
0
0
56
reading pa
Ok thanks for the help did everything i was told idles great but will not rev up don't kknow what happen to it almost rebiuld motor not giving up but stopping for a few days
 

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
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memphis Tn
Make sure the throttle is actually moving the carb slide. I've had the small ball end on the throttle cable fail and give this problem...
 

Bobbyz

New Member
Jul 15, 2014
48
0
0
56
reading pa
No luck china girl idles good turn gas to her gos up very litle will not move me on bike on flat did everything i was told i must be overlooking something .the only thing i was not shore about is took intake off piston moves but does not open intake port looked over all parts they look the same
 

Greg58

Well-Known Member
May 1, 2011
5,353
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Newnan,Georgia
The fuel is drawn down under the piston to lube the lower bearings first then it travels up the transfer ports into the cylinder. Yours is like all the piston port two strokes.
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
I've seen barrels with transfer ports just a bit lower than usual (maybe about the height of one piston ring diff) - these can usually be made to run with a really thick base gasket that some kits use or 2 or 3 regular gaskets.

I've seen so many diffs that first thing I do is put both barrels upside down on flat surface & put a straight edge across the base gasket seat - often find a few mm diff in overall height & then know to see what needs to be done with port height adjustments. But most often a new motor is quicker & easier and about same price if labor is counted.
 

Bobbyz

New Member
Jul 15, 2014
48
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56
reading pa
Ok was working on bike and found a bolt that hold both half off motor together on bottom of motor head broke off it hides behind chain gard of bicyclr chain side don't have time tofix it this week hope that's it but there no oil leaking out there
 

crassius

Well-Known Member
Sep 30, 2012
4,032
158
63
USA
yes, that could be it - were I you, I'd use a hand impact driver on all the case bolts (including the three hidden under the clutch)
 

skitchfish

Member
Oct 27, 2010
222
0
16
Michigan
Sounds like typical symptoms of an air leak at intake or intake to carb, sometimes there not real obvious. Make sure your choke is moving when you move your choke flipper
 

skitchfish

Member
Oct 27, 2010
222
0
16
Michigan
When you removed your intake to watch piston did you use new gasket? Did old one tear or come off like it was glued on? Maybe try cleaning it up with a new gasket and a thin film of seals all and allow a full day to dry. I realize this sounds too simple but give it a try.