My Sportsman 400 developed a carb problem about 4 or 5 weeks ago. Until then it ran great. Some days it will not start, but if I keep trying and let it sit about 5 minutes between times I crank it, it will ususally start and run fine the rest of the day.

I use this every weekend at the MX track as a pit vehicle.

When it doesn't start, it appears to be flooded. I remove, the air box lid and filter, and sometimes see raw gas run into the air box. So I now have the carb off and have bought a new needle and seat since I think the needle is stuck. I have a couple of questions.
1. How do you remove the part that the needle slides seats into? Does it unscrew?

2. I am not familiar with this type of carb, since I mostly work on 2-stroke dirt bikes. This carb has a diaphram that moves a slide up and down. Does it work off of vacuum? the slide is all the was down when I look at it, which to me would be similair to having the choke on.

Any othe rsuggestions?
Thanks

 

as far as i know the seal just unscrews and yes i do beleave it runs off vacume.

 

Take a pair of needle nose pliers and pull straight out on the seat, it will pull out and the new one pushes in, while you have it apart, take some carb cleaner and tremove all the jets and spray the jets and the holes out real good,and make sure they are open and clean.

 

Thanks for the tips guys. I got the new needle and seat installed into the carbuerator.
My other concern is the slide closing off the throat of the intake. The slide is blocking about 80% of the intake, which to me is the same as a choke. How does the slide operate? It seems to me it should be open more. Before I put it all back together I want to make sure I don't have another problem.
When I move the thumb throttle, the butterfly moves as it should. I pull the manual choke, but can't see anything that is moving inside the carb. How is this supposed to work or what does it move in the carb?

 

As throttle is pressed and butterfly opens,vacuum pulling from intake raises slide and needle to allow fuel air mixture into combustion chamber. Choke itself is not visible unless you remove top cap and diaphram,then can see small brass valve that open and closes with choke **** allowing fuel into chamber. Not usually necessary to remove diaphram unless rebuilding carb complete.Slide controlled by spring under cap,lift slide with thumb,should slide down smoothly.

 

<div class="FTQUOTE"><begin quote>Originally posted by: old polaris tech

As throttle is pressed and butterfly opens,vacuum pulling from intake raises slide and needle to allow fuel air mixture into combustion chamber. Choke itself is not visible unless you remove top cap and diaphram,then can see small brass valve that open and closes with choke **** allowing fuel into chamber. Not usually necessary to remove diaphram unless rebuilding carb complete.Slide controlled by spring under cap,lift slide with thumb,should slide down smoothly.</end quote></div>

So the slide is normal, with it most of the way down right now and will move up once the engine starts and the vacuum applies to the diaphram?
Can you think of anything else beside the needle and seat that might cause gas to back up into the carb? This problem occured suddenly. the bike may not start for 4 hours, trying every 15 minutes or so, then it will start and run just great.

 

the slide does work on vacume and like he said when the throttle is pushed is when it opens. its not like a choke and opens up or down. it all depends on the rmp of the engine.

 

Well guys I am stuck. I purchased a new needle and seat and installed them. I cleaned the main and pilot jets. The diaphram looks OK, and the slide moves smoothly.

I put it back together and have the same problem. The bike will not start, and gas comes back through the intake. I look into the intake when I am trying to start it and the slide just stays down. It never moves up when it is cranking and I move the throttle.

I cleaned the seal on the diaphram around the metal cap, and it moves easily if I blow some slight pressure into the intake, to simulate vacuum. Do I need to have the entire airbox assembled for it to work right?

Any suggestions on what to try next on the carb or other item?

 

Thats the same problem I am having with mine, 2001 400 sportsman, a local guy thats works on small engines said they all start hard, but I dont think that is right. Anyone got any ideas on how to slove it??
Thanks

 

Is yours running gas out of the intake? I would replace the float needle and seat and verify the float height is correct before doing anything else.