How To Adjust Carb Mixture On Honda 100 Cc ?

[Trevor]

Are the throttle speed and mixture screws readily accessible, or do I need to remove body parts?

How do the Thai mechanics set the mixture without a Krypton machine / exhaust analyser? Or maybe they can't!

Just want to get rid of the stinky, over-rich exhaust smell. Thanks.

[goldfish]

Don't know the carb or bike you are talking about. The mixture should't need adjusting, unless maybe you changed the exhaust. Is the air filter clean?

If you feel the mixture needs adjusting replace the spark plug first with a new one and run it for a few miles then remove and check the colour, it should be a sandy brown colour. Check the ideal colour from a picture on the net. Then turn the mixture screw a quarter of a turn at a time. Anti-clockwise if too rich (dark, sooty colour) and clockwise if too weak (light fawn, white colour). Make sure the engine is warmed up before clocking up those testing miles

[Japhrodisiac]

Warm the engine up, then turn the idle screw up so that the bike is idling smoothly ( a slightly high idle). Then turn the mixture screw in slowly

until the engine starts to sputter, turn it back out in quarter turn increments until the engine has the highest idle speed (engine will run most efficiently and thus have a higher idle on the correct mixture setting). adjust the idle screw for a nice steady, low idle, and you are done.

[goldfish]

Warm the engine up, then turn the idle screw up so that the bike is idling smoothly ( a slightly high idle). Then turn the mixture screw in slowly

until the engine starts to sputter, turn it back out in quarter turn increments until the engine has the highest idle speed (engine will run most efficiently and thus have a higher idle on the correct mixture setting). adjust the idle screw for a nice steady, low idle, and you are done.

I'm really sorry but this is not correct. It will give you the most economical tick-over, but will be running too weak and unable to pull a load and accelerate. Where did you learn to do this?

[Japhrodisiac]

Warm the engine up, then turn the idle screw up so that the bike is idling smoothly ( a slightly high idle). Then turn the mixture screw in slowly

until the engine starts to sputter, turn it back out in quarter turn increments until the engine has the highest idle speed (engine will run most efficiently and thus have a higher idle on the correct mixture setting). adjust the idle screw for a nice steady, low idle, and you are done.

I'm really sorry but this is not correct. It will give you the most economical tick-over, but will be running too weak and unable to pull a load and accelerate. Where did you learn to do this?

Well, this is the tried and true quick and dirty method, and works fine. Your method would have an inexperienced "tuner" pulling the plug to check for colour, regardless of whether or not he is riding on the idle circuit, or on the slide/needle or main jet circuit. Pulling a load? He is riding a 100cc honda dream, where he will be on the idle circuit (up to 1/4 throttle) for about .2 of a second until he is WFO just to keep up with traffic, lol. In a former life I was a professional motorcycle mechanic, roadraced at pro level for 8 years and built and tuned hundreds of engines. Since you asked. And, never be sorry.

[goldfish]

Am always sorry if I feel I need to correct someone elses advice, wrongly so on this occasion it would appear.

'Pulling a load? It a 100cc bike". Cheers for giving me some perspective here.

[Trevor]

Thanks for the tips guys.

Problem is the mixture is still too rich with the mixture screw hard down tight as a gnat's orifice. Guess it's time to change the carburettor, or at least the mixture jet?

[goldfish]

Thanks for the tips guys.

Problem is the mixture is still too rich with the mixture screw hard down tight as a gnat's orifice. Guess it's time to change the carburettor, or at least the mixture jet?

then loosen it

[Japhrodisiac]

Thanks for the tips guys.

Problem is the mixture is still too rich with the mixture screw hard down tight as a gnat's orifice. Guess it's time to change the carburettor, or at least the mixture jet?

It is likely then that the overly rich mixture is due to the little tip of the mixture screw being broken off due to over tightening, or that the float needle is stuck, or some such problem with your carb. Also, i want to distinguish between a fuel mixture screw and an air bypass screw on your carburetor. Carbs have either one or the other, never both. If the screw that you are adjusting is closer to the engine side of the carb than the air intake side, then the function of the screw is to adjust fuel metering on the idle circuit by reducing or increasing the amount of fuel passing by the orifice which the tapered end of the fuel metering screw controls. Some carbs (like those on 2 stroke bikes and some older design 4 strokes such as scooters etc) have an air bypass screw, which is located on the air intake side, rather than the engine side of the carb. If you turn this one in, you would be RICHENING the mixture, because you would be reducing the amount of air in the air/fuel mixture. Make sure that you know which type of carb you have, and are adjusting it properly. Remember

Air Bypass screw : turn in for rich, out for lean

Fuel Mixture screw: Turn in for lean, out for rich

Now you should be well and truly confused, but this may be your problem.

[jeffrosner]

Warm the engine up, then turn the idle screw up so that the bike is idling smoothly ( a slightly high idle). Then turn the mixture screw in slowly

until the engine starts to sputter, turn it back out in quarter turn increments until the engine has the highest idle speed (engine will run most efficiently and thus have a higher idle on the correct mixture setting). adjust the idle screw for a nice steady, low idle, and you are done.

I'm really sorry but this is not correct. It will give you the most economical tick-over, but will be running too weak and unable to pull a load and accelerate. Where did you learn to do this?

This is how I adjust the mixture on an airplane. Of course, it pays to warn your non-pilot passengers because a sputtering engine seems to upset them.