My wife and I have matching 99 Scrambler 500s. Mine has close to 3,000 miles on it, hers maybe half that. The only mods are K&N filters on both and a Polaris speedo on mine.

The problem with both of these quads occurs when riding up a fairly long slope or climbing a steep hill when the ambient temperature is 80 degrees or more. The quads will act like they are choking and then just die. This problem occurs only rarely, but I really don’t like knowing that it is most likely to happen when I am climbing a long hill on a hot day. The last time it happened it left me sitting on a pretty steep slope at 11,000 feet with a very long drop on one side.

The only fix is to wait 10-15 minutes then restart. I have tried pouring cold water over the radiator, the fuel pump and spraying cold water on the fuel lines. I have removed the air filter cover and air filter and cranked the engine with my hand over the carb intake.

Last year I posted about this problem and was advised that it was “tank-lock” which occurs because the overflow tube is either kinked or plugged and steady acceleration will cause negative pressure in the fuel tank. I replaced the overflow tubes and made sure they were routed in a manner to prevent kinking. On a couple of occasions when riding and I could tell the quad was going to quit, I have loosened the gas cap enough to have gasoline splash out. It made no difference.

Other than this complaint, the Scrambler is ideal for my riding style.

Any opinions?

 

Mine likes to spew gas out of the vent tube every now and then. I don't really know why, but it REALLY aggravates me when it happens.

 

My '99 Scrambler 500 4x4 also chokes out on long hills. When mine starts bogging, I lay on the throttle fairly hard to keep it going. It won't die unless I let off the gas. I hate pushing the throttle to keep it running. When this happens on some hills, if it instantly recovers it might wheelie over backwards.
It also bogs in water.

 

It very well could be your jetting. On my old machine i messed with my jets w/o knowing and it messed a lot up. I too had to keep the throttle on to have it run. Also at those altitudes it could be your plug.