150cc gas motor bike

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1. If you do have a spark, you need to check the gas. Make sure there is gas in the tank first! If there is you need to check the fuel valve. Most scooters use a gravity fuel feed by locating the fuel tank higher than the carburetor. The fuel usually then flows through filter and then through a vacuum operated valve. The valve has three hoses connected to it. One if from the fuel tank and is for the gas going in, one is connected to the carburetor and is for the gas coming out and one goes to the engine manifold which provides a vacuum. If you disconnect the hose from the carburetor, fuel should run out when you crank the engine (be careful to catch the gas if you do this and don’t do it with a hot engine). If you don’t see gas the fuel valve may be faulty. You can try applying a vacuum to the control port of the valve and see if the fuel flows. Sucking on the line is one way to do this (but make sure it’s the vacuum line, not the gas line if you try this!).

   If you are getting a spark and you are getting gas to the carburetor and the engine is turning over on the starter OK, it’s possible that the electrically operated automatic choke has failed. It’s supposed to operate when the engine is cold, but if it’s stuck or burned out, the mixture will be weak and the scooter probably won’t start. The automatic choke is usually a black cylindrical object attached to the carburetor with a couple of wires coming out of it as shown on the left. It’s the only electrical powered component attached to the carburetor, so it’s usually not hard to spot. If you have a voltmeter you can measure the resistance across the leads of the choke. It should be somewhere in the region of around 10 or 20 ohms. If it’s an open circuit, it’s burned out and will need to be replaced. If it seems to be OK it may be stuck, or the wiring to it may have a problem. Check to see that it’s getting voltage.

   It’s also possible that there is a problem with the carburetor and if so you may need to remove it and clean it out. If the scooter has been sitting for a few months with gas in the carburetor, the gas may have evaporated and left a sticky “gum” behind that will prevent the carburetor from working properly and which must be removed.

   If the automatic choke is OK, the starter cranks the engine, there’s gas and there’s a spark then there may be an engine problem. You need to check the cylinder compression. You need a compression tester to do this. It screws in instead of the spark plug and measures cylinder pressure. When you crank the engine you should see a reading of around 150 psi or more. If it’s 100 psi or less there’s likely and engine problem (bad valve, bad piston, failed piston rings) which will need the engine taken apart to find.
   Probably the most common problems are a dead battery or carburetor problems due to bad adjustment or build up of gummy deposits. Carburetor problems usually come on slowly though. If a scooter is OK one day and refuses to start the next day, I’d first suspect an electrical problem.

   Comment by master — 05/12/2010 @ 3:15 pm

2. Scooter Repair

   So you buy a scooter and something breaks. Who is going to fix it? Well, if you’ve bough in person from our retail store in California,? we have access to parts, shop manuals and we will have mechanics trained to fix your scooter. All you have to do is bring them in.

   But what if you are located outside of California, we have a few suggestions for you. You can try contacting local motorcycle (or better still, scooter) repair shops. If they are not very enthusiastic about working on a Chinese scooter, no worry! Have them contact our tech support department directly. We will make sure they will have the easy access to our spare parts and the technical support they need. Remember, we are the only company who actually carries all common parts in stock.

   150cc engine and transmission as used in many Chinese scooters

   You might also get some help from a lawn mower repair shop. They are used to working on small engines and the engine in a scooter isn’t all that different from the engine in a lawn mower. You can also try snowmobile and ATV repair shops.

   CVT (transmission) belt. Price ~ $40. Belt life anywhere from 2500 to 10,000 miles

   It’s not a bad idea to keep a few spares (such as a spare spark plug and CVT belt) on hand, just in case you need them (and eventually, you will). It’s a good idea to remove the CVT cover on your new scooter and read the number on the belt BEFORE you need to change it. Belt sizes vary, even on the same nominal scooter “model” and by the time it fails, the size markings may have worn off! The belt size is usually three numbers such as “835-20-30″. This would mean the belt is 835mm long, 20mm wide and has a cross section with a 30?? bevel angle.

   The best way to avoid needing repairs is regular maintenance, which means changing the oil regularly, changing the fuel filter and spark plug at the proper intervals, checking the CVT belt and air filter, checking the tires and going around the scooter at least once a month and making sure that all the bolts are tight (especially the bolts holding the muffler on). Use the recommended grade of gas (usually higher than 90 octane for most Chinese scooters) and add fuel stabilizer if the scooter isn’t going to be driven for a while.

   Though you won’t find individual repair manuals for every different Chinese scooter, they are all pretty similar and many use the same engines and transmission parts.. There are a couple of books which may help. The Haynes guide is probably the best general reference for the repair of “generic” (i.e. Chinese) scooters. The “Complete Idiot’s Guide to Motor Scooters” is pretty basic and really doesn’t give much detailed information, though it’s not a bad introduction to scooters if you really know nothing at all about them.

   Comment by master — 05/12/2010 @ 3:15 pm

3. Scooter Carburetor Adjustment

   If there’s any one component that’s more likely to go out of adjustment on your 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. 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 as shown below.

   Comment by master — 05/12/2010 @ 3:15 pm

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