revs great on idle, no power when riding

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T-lo

New Member
Feb 8, 2012
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Orange Park
I'm sure this has been covered before but i'm not finding it in this forum due to lack of details. I'll try to be as clear as possible.
I've got around 20 hours of riding out of my newest bike, and i ride almost every day. with a 66/80cc skyhawk gt5 and the new style high preformance cns carb like the one seen here - http://www.bikeberry.com/cns-high-performance-carburetor-set.html after getting the chain to align correctly and working out most of the kinks i went for a quick ride to show it off and i got some speed! i mean that this is the fastest i've been on a motorized bike yet. flyin'! a few more good rides... anyway, now i've slowed down. i would say that i've might have lost about 30% of the speed i was getting. when idling, the engine revs great and idles fine. but when i get going, i'm just not getting anywhere.
Now i've checked the spark plug boot, check the plug tomorrow, and changed the gas. chain is tight, clutch is workin' great, and starts up easy enough. Oh, I also checked the thingy in the carb to see if it was going up and down properly and it look like it is.
What do you think?
 

T-lo

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Feb 8, 2012
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Orange Park
ok. took apart carb, nothing special happened. checked spark plug. it was a little black and oily. put it all back together and tired again. not any better. - still not going very fast. is it time to check the cylinder? what am i looking for?
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
What fuel/oil mix are you using? Too much oil, as in a 16:1 mix recommended in the kit instructions, will foul the plug and can plug up the exhaust. With as much run time as you say you have I'd suggest going to a 32:1 mix using a good quality 2 stroke oil formulated for air cooled engines.

Taking it too easy during break-in isn't good either. These little engines respond well to some hard running during the initial hours. Don't feel that you need to baby them. Don't abuse it but give it some WOT (wide open throttle) time. Your engine will thank you.

What's your plug gap? Should be .025 to .028.

Tom
 

T-lo

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Feb 8, 2012
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Orange Park
well i've done some taking things apart and i noticed that after removing the top cover to check for scratches in the cylinder, none found, it didn't seal all the way around. so i've used some RTV on it and i'm waiting 'till tomorrow for it to dry.
 

2door

Moderator
Staff member
Sep 15, 2008
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Littleton, Colorado
Silicone sealer won't do the job as a head gasket. You need to make sure the sealing surfaces are flush. We recommend dressing the cylinder head against a known flat surface such as a sheet of glass and use sand paper, 280 to 300 grit, to make sure the surface is flat.
Do the same for the cylinder then use a new head gasket with the head bolts torqued to the proper value. Shoot for 120 to140 inch pounds and make sure, if you're using them, that the chrome acorn nuts are not bottoming out before they are flush with the head. Many of us discard the acorn nuts in favor of hex nuts to assure proper sealing of the head to the cylinder.
Good luck. Let us know how things go.
Tom
 

T-lo

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Feb 8, 2012
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Orange Park
thanks tom, i think you're right. how about the metal gasket it comes with? keep it or junk it? i have an extra one - will using two help, or would they be redundant?
 

T-lo

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Feb 8, 2012
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Orange Park
I've tried to ride it again now with the rtv on it and it won't run. it sounds like my friends motor did that came with a big hole in it.
 

T-lo

New Member
Feb 8, 2012
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Orange Park
ok. i followed toms instructions and got rid of the RTV and put it all back together and running but not really well. i still don't have that power when riding and spark plug is wet and greesy after a few minutes. durring idle i can give it some gas and it screems. but when riding i can't get the rpm's . What's up?
 

T-lo

New Member
Feb 8, 2012
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Orange Park
i just replaced that spark plug and instantly noticed a differance. that's what i was talkin' about! but why is my spark plug so dirty?
 

T-lo

New Member
Feb 8, 2012
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Orange Park
Nope, Choke is not on. i do use it to help me get started but it goes off almost right away. it's not on the carb either, this is one of those you mount on the handlebars
 

darkhawk22

New Member
Aug 17, 2010
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Acworth, GA
I'm having the same problem.

I have a zoombicycles engine that I bought about 1-1/2 years ago and they no longer ship to the US from Canada (at least that I know of). Anyway the motor was running great then one day I took it out and I noticed a burning rubber smell then lost power. I checked it over and didn't see anything out of the norm so I thought it was the CDI as it wouldn't crank so I replaced it. Still no luck, limited power on hills. From what I've read it could be anything from a clogged exhaust to busted seals. Any ideas appreciated.
 

darkhawk22

New Member
Aug 17, 2010
733
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Acworth, GA
The spark plug wire was a-ok, I even tried a new CDI with a new spark plug wire and double checked the gap. Plug looks like the bike is running lean as it was very very light brown. Last night I checked the crank seals on both sides and they look ok with no oil leaking out and the side compartments for the magneto and crank were both clean and free of oil and debris. I did find that one of the prongs for the clutch plate was floating around in the case, as well as, the screw and locking ring that holds the crank gear. I will replace tonight along with some locktite to make sure things are secure. I'm thinking maybe the prong or one of the other parts were rubbing against the rubber crank seal which made the burning smell and that the parts were interfering with the operation. I'm really surprised one of the parts didn't get in the gears and lock the engine up.
 

KCvale

Well-Known Member
Feb 28, 2010
3,966
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48
Phoenix,AZ
Rves great, no power on load, wet plug...

Set the 'pac man' clamp on the needle in your carb one notch closer to the top.
This lowers the needle into the jet more and thus leans the mixture out some, meaning less gas ratio to the incoming air flow.

Pull off your intake pipe, clean it up and inspect it (did you ream out all the just at the connection?), then secure it back in place with some black gasket stuff.

Put a bead of gasket sealer over the grove in the top of the carb where the tightening screw is, air leaks there are common.

Check the handlebar cable for your choke, it may have got gotten crimped or caught and the separate choke plunger in the carb may be being held open even though the lever shows off.

Hope that helps.
 

T-lo

New Member
Feb 8, 2012
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Orange Park
the new cns carb has no needle adjustments. so i made my own. it was already at the top and i took it down and didn't make a difference. now i've changed it back. the air flow screw is sealed on the new one as well. i removed the cover and the screw is still inside and i turned it almost all the way out. Also, noticed when i shut off the gas and left it to run, it would rev much smother as it was running out. Now i set the fuel vavle only slightly on and have the air screw almost all the way out. running much better. not fouling plugs