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how to tell if my fuel mix is to rich or lean


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hi everyone im new to the forum,

i got a chinese quad 4 months ago and before you start saying thats what you get for not getting a branded quad i got it for €100.

my quad occasionally back fires when i take off and if i leave it to idel it eventually sputters and dies..

any help is much appreciated.

p.s. i have the ability to work with it mechanically but i dont have any special tools :biggrin:

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The easiest way is to pull the plugs. Black = rich / white = lean and a light tan = just right.

A black dry fluffy colored plug is caused by deposits from a carburetor that is running too rich (too much gas), or excessive idling on some engines. Black smoke coming from the exhaust is a sign of a rich air/fuel mixture. The rich air/fuel mixture must be repaired before installing a new spark plug. Common causes for a rich air/fuel mixture are:

dirty air filter.

air mixture screw or carburetor needs adjusting.

choke is sticking.

carburetor float height is out of adjustment or float is sticking open.

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i was playin around with the carb adjusting that half washer on the needle changing the position of it and then checking the spark plug but every time the spark plug was black even on the leanest setting. on the middle notch it was ideling ok but now on the leanest notch she is dieing after ideling for a bit even tho the spark plug is turned black.

im confused!!! :aargh:

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if you r running rich it will actually make your plug foul and wet. the perfect colour of a plug is a dark tan colour. if it idles and shuts off and also backfires when you give it gas it is running to lean. a rich mixture will not cause a backfire. it will ccause it to bog. turn then air fuel mixture screw all of the way in gently then turn it out approx 3/4's to a full turn. then start the quad. leave it in nutral and rev then throttle the engine up and down while fine tuning the mixture. adjust it until the bog is gone then turn it back an 1/16th of a turn. that should be set pretty accurate. if you have any other questions feel free to drop all of us another line.

your friendly neighbourhood mechanic.

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i have no idea what brand it is unfortunately and i think it DID have a adjusting screw and was very very poorly done, when i was riding it fell out so there was a hole where it used to be and i had to fill it with gasket sealant... it fixed the problem. i cleaned the spark plug and ran it and it was black and it was still back firing when decelerating... :confused:

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Adjusting the air/fuel mix at idle is done with the pilot screw, it is usually found on the bottom of the carb just forward of the float bowl. You can get stuff for cleaning your filter at a dealer, just spray it on, let it soak, and rinse it off. Yes it is perfectly ok to use water on your filter, just make sure you let it sit and dry naturally for a day or so, or until it is completely dry. Some people use diesel fuel to clean foam filters.

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You have to check the carb in three diffrent positions. The needle controls about 1/4 to 1/2. The pilot jet and starter jet control up to 1/4 and the main controls 1/2+ To check the pilot check a new clean plug but accelerating only to about 1/4 throttle. The you need a new plug to check the main. Talke it up to full throttle then put it in neutal and coast to a stop while cutting the engine. This keeps the needle and pilot from fouling the plug. I suck at jetting but once you have enough experience it is almost second nature.

What is your temp and elevation?

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