Second Build, vibrating?

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bubba

New Member
Apr 8, 2011
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Victoria, Australia
hey guys, this is my first time at this forum, firstly i'd like to point out that after reading a few threads everybody here seems cheery, helpful, and most of all supportive.

This is the second bike i've built, the first one was a rather poorly strewn together cacophony of parts. I sold it shortly after building.

It's a Huffy cruiser with a 70cc China engine. Generic, haha!

Nothing special but it is alot better than my first boneshaker. Everything feels solid. I'm 16 and work full time so i don't have a lot of spare time to work on it but i just got it finished today.

Just wondering, sometimes when i get into the high revs it seems to lose a lot of power and sought of splutters. It also vibrates like nothing i've ever seen before. I've read this is because the chinese just chuck a bigger bore ontop of a 49cc crank, but i'm not too knowledgeable in this area.

thoughts?

 
L

leadfarmer

New Member
Sep 30, 2011
149
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VA
It could be getting too much fuel at wide open throttle. I understand this is a jet size issue, and someone more knowlegable than me will come along. I am on my first build.
Anyway, that is a good looking bike.
 
Matheneyr3

Matheneyr3

Member
Jun 4, 2009
98
0
16
Carolinas
Like those colors- the fenders look like Carolina blue!
.....-I'm not sure, but your tensioner may be fighting the motor mounted on top of the chain.
Anyway- Really clean looking build- I like what you've done.

-If nothing I've suggested helps.....-Don't be surprised
Richard.
 
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bubba

New Member
Apr 8, 2011
20
0
0
Victoria, Australia
i had the tensioner mounted underneath but it kept turning inwards and derailing the chain from the sprocket, bent a few spokes too. i mounted uptop and it seems okay i suppose.. i'll try underneath again to see if that makes a difference
 
Cavi Mike

Cavi Mike

New Member
Dec 17, 2011
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Rochester, NY
If it's sputtering up top it's doing what's called "4-stroking" because it's running too rich. You need to adjust the needle on the slide in the carb. The needle is held in place with an e-clip and there are 3 positions.

Where did you get your engine? I've been trying to find that exact engine, 66/80cc slant-head in black but everyone says they're discontinued, all I can find are silver ones.
 
Cavi Mike

Cavi Mike

New Member
Dec 17, 2011
189
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Rochester, NY
Down for leaner. Did you put an O-ring in between the carb and intake first? If you don't, you'll lose all low-end power once you move that needle.
 
2door

2door

Moderator
Staff member
Sep 15, 2008
16,302
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Littleton, Colorado
Cavi Mike said:
Down for leaner. Did you put an O-ring in between the carb and intake first? If you don't, you'll lose all low-end power once you move that needle.
Click to expand...
You move the clip down to richen the mix and up to lean it. Start with the clip on the second notch from the top and work from there. Check your spark plug coloration to determine which way to go. Dark plug= rich, a light color means too lean.
You didn't say what fuel/oil ratio you're running. It should be a 24:1 mix for break-in and after a couple of gallons go down on oil to a 32:1 mix. Gap your plug at .024 to .030.

As for vibrations, make sure your engine is mounted solid to the frame, both front and rear. Any slop in the engine mounts will increase the vibrations you feel. They all vibrate to some extent; some more than others.

I also agree with the tensioner issue. You should not put pressure on the top run of the chain. It should be on the bottom side. Also you'll want to secure those wires a little better to protect the connections instead of letting them hang loose.

Good luck.
Tom
 
B

bubba

New Member
Apr 8, 2011
20
0
0
Victoria, Australia
thanks guys, i tried mounting it on the bottom as secure as i could. also i used conduit on all my wiring to protect it, as recommended. i will report tomorrow as to how i go with the tensioner issue. cheers
 
killercanuck

killercanuck

New Member
Dec 17, 2009
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Wallaceburg ON
A trick you can do to keep the idler from twisting is drill a hole in the mount for a set screw, or drill into one side of your chainstay tubing and make it a lock screw. 1/8" hole is plenty and any screw jammed in will keep it from twisting into the spokes.

If you know someone with a tap&die set, can tap a bigger hole in the mount and thread in a set screw. But a little hole is better than no hole for a set screw.

Most engines will vibrate alot at a certain rpm. My winter bike vibe's like crazy at around 3500-4000, but smooths out after around 4500, opposite of yours I guess :p

nice build, and gl.
 
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