I have a 1997 Polaris sport 400cc. This will be kind of long so please bare with me. I just had the engine totally rebuilt, I have a new carb, new ignition coil, primary coil, all my vent hoses are clean and work fine, I have a new CDI Box, new spark plug, new spark plug cap, checked all my wiring and my fourn wheeler is still messing up. Here is what it is doing. It will run all day long in Neutral, it will ride around fine low to mid throttle, and when I go wide open it sputters, back fires, and then will die, a couple mins later it will start and will drive slow and idle fine but as soon as i hit wide open it does it again. I know it is not the carb because a buddy of mine has the exact same four wheeler and his works great and has no problems running. I put it on my four wheeler and the minute I hit wide open it sputters and boggs down and backfires and then goes and then sputters and dies. I have checked all my hoses on the entire four wheeler and all are clean, I even drove with the gas cap off to see if this would effect it and it did the same thing. I am totally out of options. I checked with ritter about the stater and he said that this would not cause that, so if ANYONE has ideas PLEASE PLEASE PLEASE let me know I am totally clueless. Thank you so much. Oh yeah I also changed the fuel filter, checked the rev limiter, double and triple checked all my wires and even compared them to my buddies four wheeler, I checked the throttle lever and everything seemed good. It has to be a fuel or spark problem but I am totally bummed about this and lost. The carb is out of the question because I took my buddies working carb and all hoses and put it on mine, and put mine on his and his ran great with my carb, and once i put his working carb on mine the problem still happened. I know that you have or had one of these machines so possibly you could help me. I talked to Rick Ritter and he has helped me out a whole lot and has given me ideas but I have tried all of his and I still have the same problem could you please help me out.
Thanks so much

 

I had my 98 sport 400 rebuilt and experienced the same thing as you,although not as extreme. It turned out that the new piston allowed a lean condition to occur since it allowed more air in than the stocker. A richer main jet should clear up your problem.Later

 

OK, we're gonna need more info. First, is this a totally stock unit? Does it have a pipe,silencer,reeds, anything other than stock components?The second thing is, when you hit wide open throttle, how long of a time factor before it starts sputtering? Does it do it as soon as the rpms hit maximum, or does it take a second or two before doing it? That could be important info.Let me know and we'll go from there.Bubba

 

Bubba,
I have a stock everything, I just had my whole engine rebuilt, so I guess I do not have a stock piston, Rick Ritter re built it for me and did an excelent job. This little problem was occuring before my motor locked up and is still doing after the motor is rebuilt. I did start thinking today though when it starts bogging down and acting up, I have noticed that my air coming from my exhaust stops and then builds up and then blows out so is it possible I have a clog in my exhaust that allows my four wheeler to run properly at low speeds and then causes air to flow back from a possible clog, When this acts up it happens within about 10 - 15 feet after it is wide open. I keep hearing that it is my carb or fuel lines, how is it possible that it is my carb or fuel lines if I took out my friends that works fine on his quad which is the same year as mine and all his hoses and lines and put it on my quad and put all my hoses and lines and carb on his and his still worked fine with my carb, but his which worked fine on his how is it that it could quit working once it is put on my quad????? Do you see why I have ruled out my carb. I have no other ideas, but like I said once before the way this whole thing was acting some days I could ride all day no problems, then other days I could ride 5 mins and it would be bogging and stalling, but as of now it has happened every single day that I have added new coils, to fix the problem so it has gotten worse and now happens all the time. I hope this is enough info.
Thanks,
Jdogg

 

Jdogg,
Just a quick thought.Could it be possible that you got a mouse nest built in the exhaust while the bike was down.Had a car that did the exact same thing. Cat. converter was plugged and when it was cold[i mean cold] the car wouldn't run right.All the junk in the converter would freeze solid and not allow the ehhaust to escape.Idled fine but wouldn't rev.Do you notice it is worse when the outside temp is cold?

 

I believe it runs worse in the cold and let me tell you it is cold here it has been 30 below with the wind chill for the last few days. I am going to try to check my exhaust, and check my reeds, but how do I tell if my Reeds are bad????
Thanks
Jdogg

 

They will be cracked or broken or frayed on the tips.Later.

 

Go with exhaust first. Even with a slow flowing petcock with a blockage or something causing the fuel to flow slow, it would run out farther than you're saying. Sounds like it is building exhaust backpressure and killing it. If it idles great and responds great, the reeds should be fine.Bubba