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Posted by: Raptorlegs
Being a 2001, my guess is you need to start with a compression check.
Posted by: oldyeller
Could be a choke problem.The engine will like more fuel when its cold but will run poorly once its warm if its getting too much gas.
Posted by: oldyeller
I'm certainly no expert on automatic chokes since our Viper has a manual one(as do all of my quads)..I have heard that if you disconnect the wiring the choke stays on rather than shuts off but I'm not sure about that.Maybe if you disassemble the carb you can figure out for sure how it works.One other thing you might try is using your hand over the carb like a choke since you have the air cleaner off.Try putting your hand over the carb until the engine starts to die then remove your hand and then nail the throttle.If it responds then the engine is too lean and wants more fuel...
Posted by: oldyeller
I just remembered these quads came with a little "cap" that went over the exhaust tip to really restrict the exhaust and kill the power for beginner riders...Make sure it is removed.If the engine has been run along time with this on the pipe or muffler may be clogged and will really kill the power.
Posted by: oldyeller
Could still just be a lack of power or maybe you have some transmission problems?If you can't find anything wrong with the engine I would pull off the transmission cover and take a look.You might have some bad rollers or something going on with the variator that is making it stick in high gear..Our viper has about 125 cranking psi in stock condition.I did once install an incorrect head on it that lowered the compression to about 85 psi and it still started and ran ok but was down a little on power. You shouldn't be too bad with 90 psi but a rebuild is probably in your near future.
Posted by: bradfr
I have a 2001 sportsman 90 that I am trying to fix for my nephew. This quad runs fine in its initial 10 minutes. After that it begins to bog when you try to take off. It does not stall out it just bogs and has no power. Here is what I have currently done.
1.) temporarily bypassed: fuel filter, fuel shutoff
2.) removed and cleaned entire carburetor
3.) removed air box and air cleaner
4.) began tearing into the stator area to inspect
I am running the quad w/out an air filter, fuel filter and fuel shutoff temporarily to remove them from the picture to verify that it still behaves the same. It seems to be getting fuel fine, now I am headed down the electrical path. I was just wondering if the way it is acting could possibly be caused by a faulty stator? I have been reading posts about how bad the stator covers allow dirt, mud, and water into the stator area causing premature failure. I have not taken the flywheel off yet but there is definitely mud caked all around the outside of the plastic cover and there was a bunch of leaves trapped in the cover too. Does anyone else have any thoughts on how to go about diagnosing this problem? Also, does anyone know of a service manual(pdf format) for this that can be bought online? The only ones I can find are hard copy.
Posted by: bradfr
Sorry I meant to mention that as well. Compression is 95 psi which looks ok from what I have read on this forum.
Posted by: bradfr
oldyeller,
That sounds logical but isn't the choke automatic on these machines? There is no manual choke that I can see. How can I adjust it? I am assuming it is the piece that mounts to the carb with a wire coming out of it that they call a plunger starter on www.ronnies.com.
Posted by: bradfr
I just dug into the stator area and it was a mess. Dirt build up everywhere. It has not been having any problems with the charging system so I did not bother running any tests on that. However, I did test the ignition coil per Spike's past threads and it checks out as being ok. I am beginning to think it is still fuel related. I tried disconnecting what I believe is the electric choke that is connected to the carb and I did not notice any difference in the way it ran.(still bogged when I hit the throttle) I did play with the air mixture screw a little bit and did notice quite a bit of difference when adjusting that. Even with that set where the machine runs at its best the thing still bogs. Any other thoughts? Could that plunger starter be bad or something?
Posted by: bradfr
I will check the cap on the muffler, and try your carb idea. Thanks for the help so far.
Posted by: bradfr
Well I just tried just about everything with the carb. It is bogging down all of the time now not just when it gets warmed up. I have a new finding though. I put the machine up on a stand and played with the throttle and it had absolutley no problems. It would continuously rev up to max rpm without any problem. As soon as I took that machine off of the stand and sat on it to ride it would bog. So the problem is only when the motor is under a load. Would this be a sign of bad crank seals or blow by in the rings? Like I said before it had 90 psi compression when I initally took the compression test.
Posted by: bradfr
Thank you for all of the replies. I found out what the main issue was. Do not try and tune the carb without the airbox connected. The airbox restricts the air flow to the point where it creates vacuum for the carb to suck more gas.(kind of like a permanent choke) I was tuning it without the airbox because I was constantly taking the carb off to adjust the float. So in the end the real issues were:
1.) dirty pilot jet
2.) dirty main jet
3.) misaligned float
4.) trying to tune without an airbox.
The machine runs perfect now. I am just glad it is not an electrical problem.
Posted by: puddintang
Might want to check the jetting. I had the same problem with my Pred 90. I changed the main
jet and now it is running fine.
Posted by: mkeesling
I am having the same problem, please let me know what you find
Posted by: mkeesling
I did disconnect the muffler, it didn't help.
I checked the reed valves, they looked ok, but maybe they are too week to close at high speeds ???
Posted by: gjc92
My son's 2004 sportsman 90 has been a starting nightmare for three years. In and out of the shop for the first year and a half under warranty and then last summer a new throttle assembly installed and a new stator after I suggested that after reading this forum. I am not the mechanic that most are here but am trying now rather than feeding the dealer service area.
My current problem is it starts initially great off the kick start, not great or at all off the electrical. Once it starts you get about a lap around the house and power is lost and then it dies. Will not re-kick start for about a day and repeats problem.
There was some debris in the intake into the stator and that was cleared away. Plenty of consisten spark so it seems not to be that. I tried taking the stator cover off but that is not an easy task and couldn't get it all the way off. Do you have to take the foot rest off to get it off?
When looking at the stator assembly I noticed a cable going into it. It is the throttle cable that Y's off the throttle with one cable going to the carb adn the other to the stator. I can't seem to get this cable to move by either moving the throttle or the choke. Is this supposed to be an automated movement or could it be my problem?
Thanks for any help. My son is about to turn 15 and is looking for a new machine but I just can't honestly sell this problem to anyone else. ANy ideas?
