Ok guys. I know this is the C3 general forum but I really need help. Please just give me this one thread that doesn't fit in this forum. You guys are the only group that I trust to get good advice on a motor problem from.

I have a 2003 Polaris Predator 90 2 stroke ATV that my kids ride. It starts and idles pretty good. When they take off riding it the thing dies out. It's like it runs out of fuel. But, once it takes off if I move the choke slightly to the choked position it runs pretty good but then when they stop it dies unless the choke is moved back to the all the way off position. So it's like it gets the right amount of air at idle but too much at WOT????? The air cleaner is clean, the needle and seat/float/primary jet are all clean and open. I did put a new stator and CDI box on it not long ago but since moving the choke makes it run fine I know it's a fuel/air deal. Do I have a crankshaft output shaft seal leaking? Any other ideas?

-Justin

 

it's been a while since i've had a 2-stroke but it sure sounds like a fuel issue.
1. if it isn't ridden much, iwould check the tank for crap around the inlet. I've had this on old bikes before.
2.is the fuel line kinked?
3. use a whole can of carb cleaner to blast EVERY little hole in the carb.
4. did the kids try to "fix" it in the garage? It's amazing what an 8 yr old can do with a screwdriver. You may want to check the basics; air mixture, oil mixture (if equiped) & idle.

in my LIMITED experience (3 20-30yr old bikes & 1 old piece of sh** snowmobile )with 2 strokes the crank seals don't go bad.

good luck.

 

I have 3 Sea Doo's with 2 strokes and one thing that I worry about is running them too lean. It is the easiest way to burn a piston. I am very careful about keeping fuel filters changed and I rebuild the carbs every 3 or 4 years to make sure the jets are clean. I even went through and replace all of the fuel lines to be sure that they were in good shape. Is there an ATV forum? Sea-Doo.net has given me a lot of valuable info.
Good Luck

 

Couple of ideas.

Make sure you are getting clean fuel to the carb.

A common problem with 2 strokes is that once they get some wear on the cylinder walls etc, they will run great when cold, but just won't run reliably when hot. Hope that's not the case. This happens mostly with chromed cylinder walls.

Also, don't use outboard oil in anything but an outboard. Use a good quality oil like Stihl etc, meant for high temps and clean burns.

 

It has never had anything in it for oil but Polaris oil. The fuel flow to the carb is fine. I know that because I replaced the fuel filter and when I had the carb apart I hooked the fuel line onto the carb and opened the fuel valve and saw a good stream of fuel shoot out of the inlet port on the carb body. I rode it around long enough to get it warmed up and it didn't improve the situation. Is there a way to check the vacuum on a 2 stroke?

Everytime I own a 2 stroke I always say I will never buy another one.........guess I get what I got coming for buying a stupid 2 stroke in the first place. Must be time to go to the Honda dealer and get a new 90 for the little one and a 250X for the older child.

-Justin

 

We better pray that "grumpy" dont see this , other then that I am sorry but I have no clue as to whats wrong but I sincerely hope you get it fixed for your kids. Peace,,,Moosie

 

I had this same thing happen to me. It is a dirty carb. I sprayed it out and didn't fix it. I had to take out all the jets and found a piece of sand stuck in one of the jets. took a toothpick and cleaned it out and it runs like new.

 

OK. I'll try that route. I didn't go completely through the carb, just checked the needle and seat and primary jet and flow to the bowl.


-Justin

 

might be polishing his pewter.............

 

I've been riding snowmobiles for 20+ years. I run seafoam in the first tank of the season, but every couple of years I have to yank the carbs and clean them. Good luck.
Tim

 

If the carb uses a pulse diaphram to supply fuel.Check the pulse line from the carb to crankcase for cracks. It could be leaking crankshaft seals. Just what you didn"t want to hear.

 

Pretty sure the pilot jet is plugged. At least that's what it sounds like. It's the other little jet with the itty bitty hole.

 

[QUOTE=Artsvette73;1567403109]. It could be leaking crankshaft seals. QUOTE]



based on your description of the problem, that was my first thought before I scrolled thru the posts.

Sound exactly like what older Yamaha 2 stroke golf cart engines do when the seals go bad.

 

its got water in the carb undo the screw on the bottom and drain it out.should be fine after that.ben

 

We race karts so have a bunch of 2 strokes in the garage.

I don't think it's crank seals. My experience with crank seals is they usually make it hard to start when really bad and kill the top end.

Sounds like dirt in the carb to me or fuel pump, but doubt this has a fuel pump from what you describe.

Many carbs have areas that you cannot clean without removing a brass plug (the plugs are pressed in and have to be replaced with new plugs if they are removed). Typically a full rebuild kit will include the plugs.

Seafoam works wonders as well, but won't help if it's a bit of sand or something like that.

 

I am going to take the carb off and look it over really well today. I didn't check the pilot jet when I had the bowl off last time, just the needle and seat and primary jet, along with the fuel flow from the tank. It doesn't have a fuel pump, it's gravity feed from above. I will let you all know what I find with the carb. Either way I think there's a Honda 250X under the Christmas tree for my 10 year old and a 90X for my 7 year old. But, I gotta get this thing running good before I can sell it.

-Justin

 

In our house, 2 strokes rule!

 

Hey, those are great pics. I bet the kids really like that. What do those things run for speeds? What kind of engine are they running?


-Justin

 

These are 125cc Rotax engines. The Rotax 'program' uses the same engine for 4 different age groups (7yr-Seniors) by using a combination of different exhaust, different cylinders and restrictors. The adult package is about 28hp.

Chris runs "Mini-Max" which is 9-12 years old. With the spec gear on a sprint track (short [< 1 mile], paved road course) it will do 55mph.

On a road race track with the road race spec gear (road race being a car track > 1 mile long), they will do 68mph.

IF this class had open gearing (which they do not), it would do 75 or so.

IMHO, this is not a 'starter' class for the younger kids. Starting in this class when you are 11 or 12 is fine. Chris moved to this class when he was 8, but at that point he had been driving for 4 years and racing for 3+. There are other classes (Yamaha, TaG in this area) that are for the same age group and have a lot less HP.

His other kart is a 80cc shifter. That thing will fly. While Chris is not ready for the road race track in the shifter, other boys are running 100mph with the same setup on the road race track. On the short track, the shifter is doing about 65mph, but is LOADS of fun.

The pic with the group of boys was from Eagles Canyon Raceway north of Ft Worth.

 

I think it is technically impossible for a naturally aspirated engine to get too much air. I think you mean to say the mixture gets too lean, which would be as a result of not enough fuel. I have had the speck of sand/blob of gunk caught in a jet problem on lawnmowers, snowthrowers, snowmobiles and probably a few other things I have gotten too old to remember, so I think the boys have steered you right here.