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2000 Suzuki 500 Quadmaster stumbles and backfires?


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My Quadmaster was getting very hard to start so I put a carb kit in it except the diaphram and float. Now it is running worse, it is stumbling and backfiring. I read some of the threads with similar problems and have adjusted the valves and the float and have checked the carb several times and it still runs awful. I have ordered a new fuel valve and vacuum hose to try that, I took it apart and the diaphram in it looks kind of bad. I have 4 questions:

1. Can the diaphram or float in the carb cause this problem?

2. The needle valve goes through the diaphram assembly and has an E clip with 5 settings,I have it on the middle setting, I didn't pay attention when I replaced it, which setting is the right one?

3. There looks like good fire at the spark plug, could this be an electrical issue? (CDI or Ignition coil, generator)

4. I also left the fuel valve in the PRI position over night and most of the gas went on the ground and evaporated, it did not go into crankcase. The book says this could cause engine damage, what kind of problems can this cause? It runs the same as before.

thanks for any help


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Gas running out of the overflow tube could be a stuck float, and that could cause your problem. Did you find any fuel in your airbox? The fuel valve could be your problem too, someone just posted a similar problem and it turned out to be the diaphragm in the fuel valve. I think that you are on the right track by focusing on the fuel problem. I would forget ignition issues unless you still have problems after you get the fuel issue fixed. As far as the needle clip position goes, I would consult a dealer service tech on that one, elevation, air temp and engine mods can all affect the jetting neeeds. You may also want to get a manual for it, they are a must for anyone working on thier own machines. When you had the carb apart, did you clean it? Did you notice any debris or gummed fuel deposits?

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As far as the needle clip goes, I would call a dealer tech and ask them what they recommend, but there should be something in your repair manual. Do you have an actual repair manual, or are you talking about the owners manual? If you can't get any helpful info anywhere else, I would start in the middle and see how it runs, if it seems good then ok. If it doesn't, try moving it up or down and see if the problem gets worse or better. If it gets worse, then you need to go the other way. At anyrate, I wouldn't mess with that untill you get the new fuel valve, once that is fixed, then I would start messing with the jetting.

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  • 3 months later...
  • 2 months later...

you siad two key points to your problem that did the exact same thing my atv did. when you rebuilt your carb did you remove the needle screw out of the bottom on the front of the carb closest to the engine. that screw is known as the start/idle screw. it is running to lean whenyou try to start it. you should richen it up by turning it out.

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  • 1 year later...

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