running lean

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T

t6R

New Member
Mar 31, 2014
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Connecticut
Hi guys, I can't figure out why my bike is running so lean. I know i'm getting too much air. the stock jet in it is my biggest i have. I have a jet kit that came with my other carb, but i can't get a filter on that one. Not enough space between the seat tube and the carb.

Anyways, i have sizes .60, .65, .70, .75 and .80 along with the nt stock jet and the stock jet that came with it. I've restricted the air flow on the filter by putting something over it. It runs lean to the point that it wants to take off.
 
2door

2door

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Sep 15, 2008
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Start looking for a massive air (vacuum) leak somewhere in the intake circuit or crankshaft seals. You're introducing excess air somewhere. This is almost an unheard of problem with the NT carburetor which typically runs toward the rich side. The problem isn't the carb, I'm almost certain, unless you have poor fuel delivery from the tank or a clogged or partially clogged main jet.

Start at the intake manifold gasket where it attaches to the cylinder. Make sure the gasket is sealing and the fasteners are torqued correctly. Check where the carburetor attaches to the manifold. The metal to metal clamping action doesn't promise a good air-tight seal. We suggest a sealant be used.

Remove the right and left side covers. Look for evidence of oil residue inside the covers which might indicate a defective crankshaft seal.

Let us know what you find.

We're assuming you are using a muffler/exhaust system and not running the engine with an open exhaust port or pipe with no muffler.

Tom
 
crassius

crassius

Well-Known Member
Sep 30, 2012
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if you have the steel intake, your carb may not be on all the way (happens a lot) - push a piece of thin safety wire into one of the slots in the carb mount & see if it hits steel or goes right in
 
T

t6R

New Member
Mar 31, 2014
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Connecticut
My main jet is clean. I am running a small expansion chamber. I will check the crankshaft seals though. I havn't checked the intake manifold yet. Thanks for the tips. I don't think my duel delivery is a problem. I can see fuel making it through.
 
maniac57

maniac57

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Oct 8, 2011
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I'm not at all sure you ARE running lean.
What exactly makes you think it's running lean?
Is it overheating? Refusing to shut off? Pinging and detonating?
Just a white plug tip is no guarantee it's lean. Gas does weird stuff these days.
I have NEVER seen a chinadoll that had a factory carb on it that was running lean.


First thing to do is remove whatever you have blocking the filter, then install the stock .70 main jet and start from there.
Then tune with the needle, and if it still four-strokes a lot, drop to the .65 jet.
Remember to reset the needle to full rich when swapping mains to allow full tuning range on the main jet..
 
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T

t6R

New Member
Mar 31, 2014
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Connecticut
Its idling at about half throttle. the Idle continues to skyrocket and spikes when i pull the clutch in. It almost takes when i let the clutch out without being on it. It didn't do that before when it was running correctly. I believe that it could be an air leak in the crank case. I'm missing 2 bolts. have yet to find a hardware store that has them.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
Check that the carb slide is actually moving all the way up and down by removing the filter and looking as you turn the throttle. cable could be binding or kinked.
If you're missing case screws, you may indeed have a massive air leak. I would not run it like that. The screws are common metric stuff available at any Ace hardware, Lowes, Home Despot, etc.
 
T

t6R

New Member
Mar 31, 2014
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Connecticut
home depot doesn't have anything at all in my area. Ace might have them, but they don't really have a lot either. Lowes has about the same stuff as Home depot.
 
T

t6R

New Member
Mar 31, 2014
80
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Connecticut
sorry to revive an old thread, but i wanted to post something. I figured out why it is running lean and just need some help. I have to replace the crankshaft gasket, and probably the gasket between the top end and low end. I tried to start it yesterday and found fuel leaking out of the crankcase. does anyone have a guide for replacing these gaskets? (I know the crankcase one needs replacing because part of it is falling out of the motor) Also, would it be beneficial for me to have my crank balanced? My uncle knows how to do it...so would it be worth the time and effort while i have the casing open?
 
crassius

crassius

Well-Known Member
Sep 30, 2012
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stop

first thing to do is use an impact driver on all case bolts (including the three under the clutch hub_ - this will usually fix case leaks unless your front mount is being spread by a really wide frame tube every time you tighten the mount (this you fix with some spacers there)

barrel gasket is fixed by increasing head torque by 10% or maybe even 15% (unless you have acorn head nuts that are binding which means adding washers or using open nuts)
 
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