66cc Engine won't Idle

GoldenMotor.com
B

BeaverRat

New Member
Jun 27, 2011
147
0
0
WA
Hello,
I just resolved the issue of the carburetor leaking, so now I can return to the original problem... No matter what I do, the engine will not idle. For instance, if I stop at a stop sign, I have to feather the throttle a bit to keep the engine from quitting. If I just lower the throttle all the way and disengage the clutch, the engine will quit.

The only way I can get the engine to not quit, is to turn the idle speed screw all the way in. But then it seems like a VERY fast idle... Even if I back the screw off a tiny bit, the engine quits. The strange thing is that if I turn on the choke, the engine speeds up a ton! (that's not normal is it?)

Anyway, it appears to run fine when not idling with the clutch disengaged, but it is sure annoying to have to restart the engine after every stop sign :)

Anyone know what is going on?

Thanks
 
Allen_Wrench

Allen_Wrench

Resident Mad Scientist
Feb 6, 2010
2,784
26
36
Indianapolis
Where's the c-clip on your needle set? Once I set mine into the second groove from the top, then did just a bit more fiddling, she idled fine.
 
D

dmb

Active Member
Dec 4, 2010
1,354
3
36
lakewood ca
you can check a air leak with wd40 or carb cleaner. spray if any rise or stall. i always use a o-ring and loctite290 [made for carb adj screws, i put a little on the intake too]
 
B

BeaverRat

New Member
Jun 27, 2011
147
0
0
WA
Ok. My C clip has 5 grooves on it like this

[][][][][]

The clip is on the middle notch.

Also, I am running 70:1 opti 2
 
B

BeaverRat

New Member
Jun 27, 2011
147
0
0
WA
OK, I leaned it up a notch, and it made no difference. Still very hard to start, and still wont idle unless the screw is all the way in (and even then it idles extremely fast).
 
B

BeaverRat

New Member
Jun 27, 2011
147
0
0
WA
I might just order a new carb... this one has been nothing but trouble...

EDIT: I was just thinking, could the problem be a bad spark plug?
 
Last edited:
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
No, moving the clip down, towards the pointy end, raises the needle which enrichens the mix.
I meant for you to enrichen the mix. The fact that it runs better with the choke partially on shows that it needs more fuel in the fuel to air ratio.

A new spark plug or a gap adjustment could help too
try adjusting it, ranging from .020" to .028".
 
B

BeaverRat

New Member
Jun 27, 2011
147
0
0
WA
Ok, I will richen it. But I must have a air leak somewhere because most people that run Opti 2 at a lean ratio have to lean out there engines. What are some common areas of vacuum leaks? I already o-ringed the intake connection at the carb, so it must be somewhere else...

EDIT: I richened it all the way (bottom slot on needle) and it runs and idles now, but I noticed the idle is very inconsistent. It will speed up, and then slow down, and I have to be constantly adjusting the idle speed screw otherwise it will quit, or rev too high. Does this sound like a vacuum leak?
 
Last edited:
biknut

biknut

Well-Known Member
Sep 28, 2010
6,631
409
83
Dallas
Which carb are you running, NT, or CNS? I'm guessing NT. If that's the case the middle slot on the needle is the default position. I usually have to run the needle in the leanest position.

Intake leaks are usually either where the manifold bolts to the head, or where the carb connects to the manifold. Usually if I get even a small intake leak, oil leaks out onto the fins under the manifold, and runs around to the front of the motor.

If you can get a good idle by just holding the throttle open a little, you just have an adjustment problem. Most of the time an intake leak causes the motor to race.
 
MarkSumpter

MarkSumpter

New Member
Nov 27, 2010
474
0
0
Ohio
Ok Beaver Rat like Gearnut said the problem you are describing sounds like an air leak especially since you have richened the mix and it idles but is erratic.

First off if you have the acorn nuts holding the head on throw them away and get some regular 6x1mm nuts. The acorns tend to bottom out and not actually allow the head to seal. Then remove the head and check it for trueness (warpage) and inspect the gasket for blowby and replace if necessary then re install the head and cross torque the new nuts to 100 inch ponds of torque. I would also check the intake manifold gasket and seal it with indian head and possibly put some RTV silicone around the carb throat where it goes over the intake and around the clamp relief. Return the c clip back to the middle notch.

If you still are having a problem woth surging or it still wont idle you need to do a more comprehensive leak test. Some people use WD 40 or carb cleaner but I dont recommend that method because it doesnt always detect a leak and you cant check the crank seals in this manner as well besides the fact that carb cleaner is flammable as well as was WD40 till recently and can cause injury.

When I was building my first china engine bike last November I had some serious air leaks and posted the method I have used for over 30 years working with 2 cycles in this thread:

http://motorbicycling.com/f52/basics-port-polish-port-matching-16646-6.html#post237700

BTW this thread is well worth reading in its entirety as there is a lot of information on porting from some really knowledgeable folk.... Gosh I can't believe it was only in November that I got my first China and have done so many since LOL.
 
B

BeaverRat

New Member
Jun 27, 2011
147
0
0
WA
MarkSumpter said:
Ok Beaver Rat like Gearnut said the problem you are describing sounds like an air leak especially since you have richened the mix and it idles but is erratic.

First off if you have the acorn nuts holding the head on throw them away and get some regular 6x1mm nuts. The acorns tend to bottom out and not actually allow the head to seal. Then remove the head and check it for trueness (warpage) and inspect the gasket for blowby and replace if necessary then re install the head and cross torque the new nuts to 100 inch ponds of torque. I would also check the intake manifold gasket and seal it with indian head and possibly put some RTV silicone around the carb throat where it goes over the intake and around the clamp relief. Return the c clip back to the middle notch.

If you still are having a problem woth surging or it still wont idle you need to do a more comprehensive leak test. Some people use WD 40 or carb cleaner but I dont recommend that method because it doesnt always detect a leak and you cant check the crank seals in this manner as well besides the fact that carb cleaner is flammable as well as was WD40 till recently and can cause injury.

When I was building my first china engine bike last November I had some serious air leaks and posted the method I have used for over 30 years working with 2 cycles in this thread:

http://motorbicycling.com/f52/basics-port-polish-port-matching-16646-6.html#post237700

BTW this thread is well worth reading in its entirety as there is a lot of information on porting from some really knowledgeable folk.... Gosh I can't believe it was only in November that I got my first China and have done so many since LOL.
Click to expand...

Ok, I have:

-replaced head nuts with open ended ones
-torqued head down to 12 ft-lbs
-sealed carburetor clamp with an o-ring
-checked intake manifold to engine connection with WD-40
-re-seated c clamp to middle position

AND, it still will not idle consistantly. I have to always be adjusting that idle speed screw to keep it from quiting, or revving too high. Also once I get it idling nicely, if I try to rev the engine with the clutch disengaged, the RPM's get stuck pretty high and it will not return back to a nice idle (the carb slide is not getting stuck). The only way to lower the idle speed then is to pull out on the adjustment screw. I end up just chasing the idle speed... Then the next time I go to start it, the idle speed will be way off again...

Does this still sound like an air leak?

:-||
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
Air leak can be leaking from a:
Intake seal, either at carb to manifold or manifold to cylinder.
Crankshaft seal, left or right side.
Cylinder base gasket.
Crank case center gasket (where the left and right halves meet).
Head gasket. The head and cylinder gasket surfaces are notorious for not being flat and true. Even with replacing the head nuts with the much better standard nuts as you have done, and proper torque, if the sealing surfaces are wavy then there is no way the head gasket can seal properly.
 
You must log in or register to reply here.
Top Bottom