Clutch New 48cc Engine, clutch noise

[AussieSteve]

The instructions had pictures of the internal carb parts and it says exactly:

The Air/fuel mixture screw (idle) should be preset at 3.5 turns counter clockwise from the totally closed position. DO NOT back off screw more than 4.5 turns or vibration may loosen the screw and cause it to fall out. <happy cheapskate notes, spare included in kit> If this situation occurs, stop engine immediately and replace mixture screw.

Are we talking about the NT carburettor supplied with most 2-stroke engine kits? If so, there is no idle mixture screw, only an idle speed screw. This is not an Air/fuel mixture screw.
From the above, it sounds like you're talking about a totally different carby. (or I am.)
(Post a pic if you don't mind.)

By now, poor wrinkledoggi must be totally confused.

... Steve

 

[happycheapskate]

post pic: ok

Hi wrinkledoggi. I hope you are not confused.

Perhaps Aussie is right and we got different carbs. I thought these things were pretty common or universal, but maybe I got an upgrade or variation.

Picture to come (editing post after upload)

http://tinypic.com/m/6jd24m/1

 

[motorpsycho]

throttle cable adjustments shoudl not be made at the carb cap OR by raising or lowering the slide c-clip. as aussiesteve pointed out, the c-clip is for adjusting lean/richness of the air fuel mixture. Throttle cable adjustments should only be made by the adjustor on the cable that is up by the throttle. like aussiesteve said, if you adjust it in any other fasion, your cable could become too short, and it will pull the throttle open when you turn the handlebars.
by raising the carb cap the thickness of the o-ring you used, will change the air fuel ratio (richer) because you are pulling the jet needle out of the main jet the thickness of the o-ring.

on my 48 c.c. i did not have to make any internal clutch adjustments. all my adjustment was made at the clutch arm by the length of the cable. when your clutch is engaged (clutch lever out) you should have a little free play in the lever / clutch arm. the free play will ensure that the clutch is fully engaged when you let the lever out. with the clutch lever out, you should be able to wiggle the clutch arm back & forth slightly with your hand.

you do not have to peddle your bike to start the motor. normally (well, with me anyway) i just get a rolling start and pop the clutch. I NEVER peddle my bike, i just roll down the driveway and pop the clutch. the only thing i use my peddles for is the coaster brake.

happycheapskate: once you get your motor running, the only way to tell how it's running mixture-wise (too lean / too rich) is by reading the spark plug. you will have to run it and check the plug. as i understand the correct way to do it is to ride the bike at w.o.t. and then kill the motor with the throttle held at w.o.t. pull the plug out and "read" it at the electrode. if it's black the mixture is too rich, if it's a silvery color it's too lean. tan is the color that you're after.

 

[happycheapskate]

It only has one screw. The internals include a "depth setting" of the needle (relative to the sliding air valve ) which is manipulated by setting a clip on the needle to change its positioning. I like the design.

I used blue low strength loctite on the carb screw for a extra safety. you can still turn it but it won't rattle loose. I suppose a bit of plumbers tape or the home remedy of nail polish will work as well. Yes it still has the spring too.

 

[happycheapskate]

motorpsycho. Thanks for the tip. I thought mine is a little rich running because of the sound and characteristics of how it runs across the RPM range. (just used to weedeater carbs, but they usually have 1 or 2 mix screws, an idle screw, and 2 limiter screws).

I think the clutch is maladjusted because its scraping a little when I pedal only with motor off, and when I pedal with motor idling, it speeds up a little.

By moving the arm by hand, it still seems this way, so I will try a small adjustment to clutch.

Its close enough for now because the screw is working for adjustment,

 

[AussieSteve]

by raising the carb cap the thickness of the o-ring you used, will change the air fuel ratio (richer) because you are pulling the jet needle out of the main jet the thickness of the o-ring.

Hi motorpsycho. I agree with everything else you said, except...
Adding an 'o' ring or washer under the cap doesn't raise the needle. The spring still holds the needle firmly into the slide by pressing on the 'c' washer to hold the 'c' clip hard against the bottom of the slide. The needle height is identical in relation to the slide.
Believe me, I have a fibre washer in the top of my carb for other reasons and it doesn't raise the needle.
I've attached a sketch.
On mine, however, the additional seal did make the mixture a little richer. The carb used to suck air past the top cap before I fitted the washer. (I tested with carby cleaner with and without the washer.)

... Steve

 

[Al.Fisherman]

" The Air/fuel mixture screw (idle) should be preset at 3.5 turns counter clockwise from the totally closed position. DO NOT back off screw more than 4.5 turns or vibration may loosen the screw and cause it to fall out. <happy cheapskate notes, spare included in kit> If this situation occurs, stop engine immediately and replace mixture screw. If a more rich gas mixture is required you can move the jet pin "pac man" clip <c clip> to the next lower position notch."

This screw is misnamed if called a Air/fuel mixture screw. IT IS A IDLE ADJUSTMENT SCREW nothing more nothing less. The 3.5 turns is a good start to where it will set the piston for a idle that the engine will run. If you remove the piston you will see a milled surface cut into the piston, not to be confused with the alignment grove. This screws ONLY function is to limit the travel of that piston in the DOWNWARD movement only. By decreasing the travel of the downward movement you are letting less ambient air pass through the venturi. Thus decreasing the RPM. The mixture adjustment is done from within the carburetor and is done with the "C" clip. This is done by changing the position of the "C" clip on the needle. The closer to the top of the needle the "C" clip is the more the needle enters the jet, thus restricting both the fuel/air mixture. The pistons purpose is much that of a butterfly in a conventional carburetor.
Other then sealing the carburetor from ambient air, it will take up slack in the cable...not much, but some. The thickness of the compressed "O" ring.

 

[AussieSteve]

Thanks Al.

... Steve

 

[happycheapskate]

Thats what I got from looking at the parts too. The people in China may not worry about being totally technical with the instructions (like calling the primer button a "tickle bulb". hahaha.

Thanks for all the help on this forum, and for helping wrinkledoggi. I'm having a good time here and learning a lot. Good website.

" The Air/fuel mixture screw (idle) should be preset at 3.5 turns counter clockwise from the totally closed position. DO NOT back off screw more than 4.5 turns or vibration may loosen the screw and cause it to fall out. <happy cheapskate notes, spare included in kit> If this situation occurs, stop engine immediately and replace mixture screw. If a more rich gas mixture is required you can move the jet pin "pac man" clip <c clip> to the next lower position notch."

This screw is misnamed if called a Air/fuel mixture screw. IT IS A IDLE ADJUSTMENT SCREW nothing more nothing less. The 3.5 turns is a good start to where it will set the piston for a idle that the engine will run. If you remove the piston you will see a milled surface cut into the piston, not to be confused with the alignment grove. This screws ONLY function is to limit the travel of that piston in the DOWNWARD movement only. By decreasing the travel of the downward movement you are letting less ambient air pass through the venturi. Thus decreasing the RPM. The mixture adjustment is done from within the carburetor and is done with the "C" clip. This is done by changing the position of the "C" clip on the needle. The closer to the top of the needle the "C" clip is the more the needle enters the jet, thus restricting both the fuel/air mixture. The pistons purpose is much that of a butterfly in a conventional carburetor.
Other then sealing the carburetor from ambient air, it will take up slack in the cable...not much, but some. The thickness of the compressed "O" ring.

 

[Al.Fisherman]

Steve....Very nice drawing...so right you are. Actually if one takes the carburetor apart all this we are describing will/should become much clearer.