ok this isnt normal

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bulljo

New Member
Jan 5, 2013
34
0
0
orange county
Ok i just replaced my crank bearings and i have the following mods... ported cylinder, ported intake, shaved head, hp airfilter, ported banana pipe, petcock from a moped and a 36t sprocket on 26inch wheels. I run octane booster and b8hs plug gapped at .025 and with the carb tuned all i get is 30 mph from her. And theres this knocking at top end maybe this crank is a dud or the timing is off or is it possible for a banana pipes silencer cones to get plugged? Shoot some suggestions guy ill do anything. Btw theres no leaks.:-||
 

ddesens

Member
Jun 27, 2011
173
0
16
New Port Richey, FL.
I would pull the head off and check the top of the piston edges for shiny spots where it is hitting the head possibly. Happened to me a few times. added an extra head gasket to compensate. It would restrict your engine rpm's if its hitting.
 

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
does it have lots of vibes at the top speed of 30mph?

If so crank being poorly trued and seriously out of balance could be the problem as has been mentioned but also since you say you shaved head down piston hitting head could also be an issue if head was shaved down to far for being used with one head gasket as has also been mentioned.

My question is, have you run this engine combo in the past before the main bearing change?

if so did it have a top speed higher than what it currently has?

Map
 

rogergendron1

New Member
Sep 18, 2013
882
2
0
42
woburn ma
i get 35mph on a 44t with a puch head heavy porting, port matched, piston ramps, skirt cut for intake, cns v3 carb, and a free flowing pipe.

your probably not tunned right ... i need to see a pic of your motor and a pic of your plug.

i need your motor size and type also

does it vibrate a lot or is it smooth ?

also what carb do you have ???

it sound like (without knowing all of this info) that your carb is out of tune and you have a air leak somewhere !and also despite popular myth the higher the oct the cooler it burns the higher the comp the higher the oct needed ... adjust plug to warmest you can run with the comp and and octaine lvls you are running to get a full clean burn.

ohh and your plug is too cool try a b5 or 6hs, despite comon myths higher octain burns cooler than lower octaine !!!
 
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bulljo

New Member
Jan 5, 2013
34
0
0
orange county
Heck yeah theres vibes its more of a rattle then a vibration at top end but it sounds like it revs as high as usual with the clutch pulled in but only goes so far when i ride. Ive ran this crank and mods before no prob and got at least 40. I changed the carb for a spare i have and no difference. Its a 66 cc and the wrist pin sits lower on the piston. Ill check the piston for marks get a fresh gallon of 91 with a dose of motorcycle octane booster and also a hotter plug. Oh yeah the magnet moves a hair back and forth cuz the woodruff key is smashed so ill fix that and change my petcock for the orignal one as this is my first time using it.
 

FMB42

New Member
Sep 27, 2013
107
0
0
Idaho
How did it run before you modified it?

Did you do one modification at a time, a few at time, or all of them at once?

If you did more than one or two mods at a time, your chances of knowing what's wrong is greatly decreased.