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Why is My Moped Slow
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Technical Advice

  •  A few things you need to look at when trying to troubleshoot your moped.  How does it sound?  If you run it wide open throttle when warmed up, does it peak out? or stutter? is it loud, or very quite?

  • The symptoms can help decide what to try. When you are going full throttle, the engine should get to a high RPM and sound smooth. Things that will make the engine sound or run different-

  • Plugging air intake- will start well cold, but be hard to warm up and not reach top speed. Engine will stutter at high RPM.

  • Open air intake- to much air or air cleaner is disconnected- engine will not have power at high speed, make vacuum cleaner sound. Acts like it is running out of gas. ( sounds almost the same as a dirty carburetor.)

  • Plugged exhaust port-  Engine sounds and runs good, but has no power. Slow take off. Same as plugged muffler, but if the muffler is plugged you get a very smooth exhaust note at idle. Hmmmmmmmmmm  instead of  pop pop pop pop

  • Fouled spark plug- backfire. If you get backfire, pretty good chance the plug is fouled.

  • On models with belts, the gear ratio drops as the belt gets thinner (most hondas have belts).

  • On a moped with high mileage, the belt will cause slow top end speed if worn thin.

  •    If you have a bike with chain drive in oil bath (razz, suzuki FA 50, ) and you OVERFILL the oil amount in the chaincase, that makes for slowww running as it requires too much power to turn the oil.
  •    If your engine does not rev up well, and stutters or sputters, like when it is cold with the choke on, the engine is running too rich. (too much fuel).

  • Is the air filter soaked with oil? Clean with soap and water!

  • Is the air opening in the airbox plugged? Very common for a spider or mud wasp to build a nest in one of the intake holes .

  • On a razz, it is common to get a leaf stuck in the intake port of the airbox, causing a 10mph drop in top speed.

  • Don't try to adjust the screws on the side of the carb to get lean or rich, as they are for the idle circuit only.

  • The idle airscrew should be about 1 1/2 turns out on most bikes.

  • Say your engine revs but kind of wheezes, or acts like it runs out of gas?

  • It is common to have a buildup of hard scum on the inside diameter of the hole in the main and pilot jets, and it must be carefully removed.

  • If your moped does not idle the pilot jet is likely plugged.

  • Anytime a moped has not been used for 1 year or more, and still has the same fuel in it, good chance you will need to clean the jets.

  •   The poor quality of today's gasoline's have made this a rather steady bet.

  • Mopeds are affected more than most vehicles because  the small size hole the jet requires is easily plugged, even by thick oily fuel, or water.

  • Drain your carb once in awhile!  Most have a screw of some type at the bottom (where the drain needs to be) of the carb.  
                                                        
Other tips:
  • Make sure the air boot to the airbox is not on wrong, kinked, hard and shrunken (QT 50)

  • Don't oil the air filter if you got the stutters.

  • On a spree, you can leave one snap loose on the airbox lid to allow it to crack open, to get full rpm.

  • But, beware, to much lean out on the gas, and since the fuel cools the piston, the piston can MELT.

  • Still slow?  Check the muffler tip. Make sure no carbon buildup is inside the tip, stick something in as far as it will go.

  • Common on razz to have the tip bent over on a curb, then carbon up solid. common on all types to have the whole muffler plug.

  • When you have the muffler off, is it heavy?

  • Can you get the baffle out to see if the holes are plugged?

  • Check the exhaust port on the cylinder.

  • If you can't see all the way in to the piston, use a mirror and a flashlight to make sure the piston is ok and the port is not plugged where it meets the piston.

  • Common on all models to plug here, Just scrape it out so the hole is full size again.

  • Don't worry about the small film on the inside of the port, I am talking about a very thin film that forms a wall in the exhaust port right next to the piston.

  • A 1 1/2 inch hole can be reduced to the size of a pea...... With a thin film of carbon.

  • If you can see the piston ok, it's not the problem.

  • If you are in doubt regarding your exhaust pipe being plugged, put your hand behind the muffler to see how much pressure is expelled. compare to another bike.

  • It should blow pretty good, and have a distinct pop pop pop pop sound while idling, not a steady hhhmmmmmmmmmmm.


If you are still struggling,
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Scooter Therapy Inc
 
   
12 North Few Street  |  Madison, WI 53703    
toll free 1-800-411-1543  |  local 1-608-255-1520    

fax 1-608-255-1587  |  E-mail


Scooter Therapy Inc    

12 N. Few St     
Madison, WI 53703 

toll free 1-800-411-1543    
local 1-608-255-1520    
fax 1-608-255-1587    
E-mail

Hours: M-F, 9-6 Saturday, 10-3  CST



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Scooter Therapy inc.