how to Fix It - page 1

If there's any one component that's more likely to go out of adjustment on your scooter (especially perhaps your Chinese scooter!), it's the carburetor. If it does go out of adjustment lots of things can happen. It can make the scooter hard to start, it can make the scooter slow to accelerate, it can cause the scooter to idle badly and stall or it can make the scooter idle fast so that it's trying to go all the time and needs the brake to hold it stationary. None of these things are good.

What the carburetor does is regulate the amount of fuel and air which are supplied to the engine. To go faster you need more fuel and more air and they must be in the right proportion. The fuel also has to be atomized as much as possible (i.e. be supplied in tiny droplets). The carburetor controls all these functions and generally does it quite well.

The type of carburetor used on most 150cc GY6 type engines is a Keihin style CV carburetor with a 24mm throat. Keihin design carburetors are a well tried and tested design developed in Japan (Keihin is a region near Tokyo).

Without removing and disassembling the carburetor, there are only two adjustments you can make, but these should take care of most minor problems. The first is the adjustment of the idle speed.

Above is a picture of a typical GY6 engine carburetor and the view is that from the right side of most engine configurations on 150cc Chinese scooters. There's a small spring loaded screw which adjusts the idle speed. It's right next to the throttle control which is connected to the twist grip on the right handlebar. On most 150cc scooters, idle speed should be around 1500rpm when the engine is fully warmed up. Don't make adjustments when the engine is cold. Take a 5 or 10 minute ride first. When the engine is cold the automatic choke is in operation and that can change the idle speed. If you have a tachometer, setting the speed is easy. If you don't, you want to set the speed to a low idle. Fast enough so that the engine doesn't stumble or stall, but slow enough that the clutch doesn't engage and try to move the scooter forward. On most scooters from 50cc to 250cc, this will be somewhere in the 1500-2000rpm region.

The other adjustment you can make is to the low speed fuel/air ("mixture") ratio. This is done on most scooters using a screw adjustment on the other side of the carburetor.

This screw changes the air to fuel ratio at low speeds. It shouldn't need much adjustment, but the way to do it is to turn the screw very slightly (1/8th turn) and see if the idle speed goes up or down. If it goes down, turn the screw back 1/8th turn to where it started, then 1/8 turn in the other direction and see if the idle speed goes up or down. If it goes down, turn it back to where you started since you didn't need any adjustment! If the idle speed goes up, continue turning the screw in 1/8th turn steps until the idle speed is at a maximum. If it starts to go down, turn it back to get the maximum idle speed.

You may need to go back to the idle speed screw to lower the idle speed if it's now too fast. So the basic procedure is to set the fuel/air mixture to give you the fastest idle, then use the idle speed adjustment to set the speed to the lowest rpm that gives you smooth running.

If the scooter idles well and runs fine at low speed, but has problems at high speed, the problem may lie inside the carburetor with the main jet. The fuel/air ratio at higher speeds is set by the jets inside the carburetor and to get at them the carburetor has be be removed and disassembled. This can be a tricky job as the parts are small and delicate. The good news is that these carburetors are quite cheap. You can get a new one for $50-$60, so if you can't make your scooter run smoothly and you don't like the idea of taking the carburetor apart, you can always replace it!

Changing the engine and transmission oil in a 150cc chinese scooter with a 4 stroke engine. The procedure should be pretty similar on 50cc and 250cc models with 4 stroke engines. 2 stroke engines mix gas and oil and so have no engine oil to be changed. I'd recommend changing the engine oil at least every 1000 miles, and the transmission oil at least every 2000 miles. Regular oil changes are the easiest and cheapest way to maximize the life of your engine. Scooters take so little oil that it should cost less than $5 to do and once you know how to do it it should take you more than 10-15 minutes. It's time and money well spent.

The first thing to do is to warm up the engine. Run it for a few minutes so that the oil is warm. That way it will flow easier. If you run it until the engine is hot, or you change the oil after you come back from a trip, that's OK, but you run the risk of burning yourself on the exhaust or with the hot oil. Be careful.

Find some level ground and put the scooter on its center stand. If the ground isn't level you won't get an accurate reading of the oil level when you put the new oil in. To change the engine oil you'll need a wrench to remove the oil drain plus, a flat dish container with a capacity of about 1/2 gallon and a funnel. First remove the "dipstick" which you use to check your oil. I'd also recommend you wear rubber gloves, or at least on on the hand you use to remove the oil drain plus. On most scooters there is a spring which will push the plug out when you have fully unscrewed it and oil will pour out of the drain hole, all over your hand. It's just messy if the oil is cool or warm, but if the oil is realy hot it will burn your hand. So wear a glove to be safe.

Give the oil a minute or two to drain out. Make sure the filter is clean and then put the filter, spring and drain plug back. The spring sits on the plug and the filter sits on top of the spring with the mesh basket inside the spring. You'll have to compress the spring to start the drain plus screwing into the engine, but once

it does start, tighten it up by hand to make sure it's not cross-threaded. If it screws in easily, it's OK. If it doesn't want to tighten, you've probably cross threaded it, so try again. Finally tighten it up with a wrench. It should be tight, but don't overtighten it. The seal is made with a rubber "O" ring. You just need to tighten it enough so that it doesn't vibrate lose (which would be a disaster since all your oil would drain and the engine would seize!). The recommended torque on the drain plug is 1.4 kg.m (about 10 ft.lb). Now you can add the new oil. It goes into the same hole as the "dipstick" fits in. You'll almost certainly need a small funnel to get oil into the filler hole without spilling it. Check your user manual for the recommended oil type, but on most chinese 4 stroke scooters, regular 10-30W or 15-40W engine oil is used. I use Castrol GTX 10-30W. You can get a 5 quart bottle for around $12 (try WalMart) which is good for at least 5 oil changes on a 150cc scooter. You can also use a synthetic oil blend if you wish, though pure synthetic oil isn't usually recommended. On a 150cc scooter you'll need about 0.8-0.9 liters which is just under 1qt. As you add the oil, check the level with the dipstick from time to time and fill to the recommended level. When you have the right level, screw the dipstick back in and you're done!

Changing the transmission oil is also very simple. Most scooters recommend changing the oil at least every 2000 miles. At the rear of the CVT on the left side of the bike there are drain and fill plugs for the transmission. Place the oil drain container under the drain plug. Now remove the filler plus first, then the drain plug and about 100 to 200cc of oil will drain out. There should be a sealing washer between the drain plus and the transmission casing. On my scooter it's a thin aluminum washer. Make sure it's there and then screw the drain plug back into the transmission case. To refill the transmission, you squirt oil into the fill hole until it runs back out. That's your level check! Use the recommended oil, which in most cases is 80W-90 gear oil (though a few bikes may recommend using engine oil). To get it into the small hole you can use a small funnel and a short length of small diameter rubber hose, a syringe or even something like a turkey baster! All you need is something to squirt 100-200cc of oil into the hole. You may be able to buy the oil in a plastic bottle with a long plastic tip, which you can use to directly squirt oil to the transmission fill hole. When it starts to run back out, it's full and you can replace the fill plug (note that it too should have a thin aluminum sealing washer).

Now run the engine for a minute or two, then check the oil level and add more if necessary. Check for any leakage around the drain plugs. If all looks OK, you're done for another 1000 miles.

Scooter Maintenance
Carburetor Adjustment
Scooter Oil Change