Quantcast
Jump to content

  • Join Today, It's Simple and FREE!

    As a member, you can post in our forums, upload your photos and videos, use and contribute to our downloads, create your own member page, add your ATV events, and even start your own ATV club to host your own club forum and gallery.  Registration is fast and you can even login with social network accounts to sync your profiles and content.

Brian Haley

Early 2000s Polaris Trail Boss 325 4 Stroke Fuel Issue

Recommended Posts

I wanted to ask this question before I pull this thing apart and dig into the carb. Very seldom used for a couple years but took it out the other day and it ran like crap. Blows black smoke on throttle (unburnt fuel) and sound like a multi cylinder engine with a misfire. Won't rev very high on full throttle but seems to be smooth at about 1/3 or less throttle. Choke doesn't seem to do anything and thinking perhaps it's stuck closed. If I turn off the fuel and let it run for a minute It will rev like normal under full throttle until it stalls out from no fuel but as soon as I open the fuel line again it goes right back to running rich/flooding.

 

Any help or ideas would be great. Trying to avoid tearing it apart and rebuilding the carb but the only thing I can think is the choke is stuck cause with the fuel off it will rev just fin seemingly as it's emptying the float bowl.

Share this post


Link to post
Share on other sites


Most likely what you think it is. Usually the carburetor is the culprit here, take it off and clean it good.  If your not familiar with doing this you can go to YouTube and you will find a ton of videos to help you out. Also some fresh fuel and a new plug should fix it up. 

 

Share this post


Link to post
Share on other sites

Update and I hope someone can shed some light on this. So I cleaned the carb and no change in fact it seemed to get a little worse but I now believe that's because it needed some adjusting that I couldn't really do because of the way it was running. I still thought it was a fuel issue and it may very well be but I bought a new carb. It was cheap enough on amazon so I went that route. Installed the new carb and it starts and runs at idle better than before and smells much less rich but it would still not rev on throttle. It revved a little better with the choke on but still backfired and popped pretty badly and would not rev very high. I started thinking it could be timing so I did some searching and I found that was not likely the case but many people were saying it will run like crap without the air box installed and sealed. I had my doubts but I tried it anyway and it was the same. Without the airbox I tried covering the air intake and it flooded with fuel and stalled as would be expected. Once I put the air box on I covered the air intake again and it revved then began to stall so I covered half of the opening and bam it revs like it should.

I'm debating covering half the opening with some duct tape and just go with it but I figured I would ask if anyone had any ideas for a proper fix. I suppose the issue could be not enough fuel in the mix or too much air since it idles fine but I'm not completely sure how to adjust it. Mixture screws are usually meant to adjust at idle and my issue is off idle with both the old and brand new carb.

Does anyone have any ideas?

Share this post


Link to post
Share on other sites

Topic moved to Polaris forum and added manufacturer to topic title 🙂

Share this post


Link to post
Share on other sites


I don’t think the tape is a good idea. I would go back to the factory carb and set your fuel/air screw to 2-1/2 turns out from a snug tight position.  That should get you running enough to tune it. Either 1/4 turn in or out. The higher it revs while turning the better. Lower the idle if the engine revs to high. 

Now as far as not running right and air box etc.  Yes the air box and filter need to be in place. And that needs to be done prior to adjusting the fuel/air screw.  

Now after that is done you should check spark quality as well as add a new spark plug.  Make sure you have a good spark.

Is the fuel fresh ? And the valve (petcock) on the tank flowing good fuel ?

 

 

Share this post


Link to post
Share on other sites

I would also check the quality of your filter boot and intake boot for cracks, ect. Make sure they are all tight.

Sent from my SM-N920V using Tapatalk

Share this post


Link to post
Share on other sites

In your initial post you described a rich fuel condition that got worse as you increased throttle. You were right too think along the line of a choke stuck closed or other obstructions in the intake. Next you removed and cleaned your carb to no avail. There is one item often overlooked when cleaning a carb. The needle jet which sets just above the main jet. It is a small (usually brass ) tube with a series of small holes in the side. If those holes are restricted or clogged your fuel mixture will be too rich. Make they are clean and be careful not to alter their size. Your new carb on the other hand has a lean condition and most likely could be corrected with a larger main jet. 

Share this post


Link to post
Share on other sites

For the time being I'm gonna close off part of my air intake of the filter box cause I need it for tomorrow and it will run decent. Unless I'm wrong and the pics I found online are also wrong it doesn't appear I can adjust the air/fuel mixture screw with the carb on the quad.

One part of my question was overlooked. Am I correct in thinking that the mixture screw only adjusts idle mixture? One more thing. On the bottom of the float bowl there is a nipple with a shut off screw next to it. The original carb had nothing connected to it and the replacement had a rubber hose on it but I have no idea where it should be connected. What is the purpose of this nipple? It appears to just be a way to drain the float bowl.

Share this post


Link to post
Share on other sites

You are correct on the idle mixture screw. The rubber hose should be routed down to the bottom of the machine and left open. It is a drain hose.

Share this post


Link to post
Share on other sites


Regarding the drain hose...it's also connected to the overflow tube inside the float bowl.  If the float valve ever sticks open, the excess fuel will run out on the ground instead of filling up the crankcase with gas.

You'll need one of these tools to adjust the idle mixture with it running.1519871349_s-l1600(2).thumb.jpg.e453529e4c76ffb4e87d4c137fd2ff38.jpg

Share this post


Link to post
Share on other sites

Starting to think I have multiple issues going on. Going to replace my very old and worn fuel lines to make sure none are collapsing off idle as that explains getting too much air and backfiring. Also I ordered a new petcock cause the original does not fully shut off the flow. (noticed that when I had the tank off the quad) It's only a drip but I still want it to shut off. Once that is done I'll have to see how it runs off idle and continue to figure out why I'm having mix issues. I appreciate all the info. 

Share this post


Link to post
Share on other sites
3 hours ago, Ahren Longo said:

may have a stuck float in the carb. That will make it flood too.

The old carb didn't idle all that well but was seriously bad off idle. The new carb idles fine and still has issues off idle which leads me to believe I had 2 problems. Old carb off idle seemed to be flooding gas based on black smoke and raw fuel smell. New carb seems to be either starving for gas or just getting too much air cause similar sound with no rev and sputters and backfires but no smell or smoke and choking the air intake partially it smooth's right out and revs fine. Going to replace all my fuel lines to make sure I don't have any collapses.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Similar Topics

    • By Squirrel
      Several months ago, I finally got around to fixing the bayou. Rebuilt the carb, replaced the fuel selector switch, hoses and fuel filter, and she ran great. Only had 2 minor issues since then where, at higher speeds, it acted like it was choking out when I let off the throttle.
      Lately I've noticed if I let it go for more than a week, it almost drains the battery dead trying to start. I initially thought battery, but after inspecting I found very little if not any fuel flow through the line until it starts and runs.
      I'm a little baffled and don't have much time to mess with it as most my free time right now is spent on getting my rv up and ready for hunting season in the next 3 weeks. So any help on quick diagnosis checks would be helpful. Otherwise I'll just keep starting it every 3-4 days to keep things primed until I'm done hunting.
       
      Oh, and another question on a different topic. Does anybody know what the mounting brackets on the front rack are for? I'm referring to the 2 angled metal tabs with threaded holes that are located on the left, near your knee when sitting on the quad?
       
      Sent from my SM-G950U using Tapatalk
       
       
    • By Dra O
      posted a while back - it was running at one point - I have all the plastic shroud off - it's down to frame and engine now
      -fuel pump: when line from petcock is attached, no fuel comes out other side to carb; the line to the carb is open (can blow through it); I thought when I cranked engine that the pump would spit out fuel on other side but it does not; I removed fuel pump and opened it up - diaphragm looks good - but internal areas had lotsa calcification build up - I cleaned this out and dried it good - the clear plastic pieces (?diaphragms) aren't broken - the spring w/ steel ball on end moves freely; am putting it back on tomorrow; but can anyone answer about the pump? isn't it supposed to pump fuel through it... to other side... to carb? puzzling
      -along with fuel pump: I replaced petcock 3 weeks ago (gas tank had rusty fuel in bottom - cleaned it out prior to new petcock); when I turn petcock arrow NOT to on or reserve, fuel comes out of line; when I turn it to on or reserve, fuel doesn't come out; puzzling
      -I don't know what's on back of fuel pump - it's a valve that has a hose coming out of it - looks like it goes to engine/carb - I haven't traced this out yet - what is it?
      -can squirt gas on air filter and engine will run for 2-3 seconds then stop - fuel in top of carb (under diaphragm) does same
      -it likely needs carb rebuild - will get to this - but something isn't allowing fuel to get from fuel pump to carb
      -I THINK it has a mikuni model x carb - diaphragm is ID 26mm  OD 68mm - hard to find inexpensive diaphragm, I guess because it's a model x
      -last thing - I replaced solenoid due to old one clicking; I HAVE to be charging the battery or it won't start/turn over - battery just goes dead; but if charging, it'll turn over nicely; i'm guessing it's a bad battery
      -any help appreciated - I've never owned an ATV before - inherited this beast from grandparent in-law
    • By Arizona
      Went shopping on Saturday, picked up another Kawasaki Bayou 220 and a Yamaha Timber Wolf 250
      I really should sell some of these but they are a lot of fun to find, fix and ride
      Of course neither of them run but that's part of the fun!  Az



    • By raybob
      I have it all but can find where the vacuum line on the carb goes its a 2000 suzuki 500 quadmaster I know where the two vent lines go but not the bigger vacuum line goes it has vacuum on this line. need help. Ray
       
    • By ATVNetwork
      When it comes to adding more power to your ATV, the first thing that usually comes to mind is bolting on a slip-on exhaust. However, that usually means you are also bolting on a lot more noise. HMF do...
      More...
  • Similar Tagged Content

    • By Travis Mitchel
      Hello all just recently acquired this atv which as you can see in the pics that it has had an unsheltered life. i did get it running and put some used tires on the front.
      It still needs a bit more well needed maintenance, chains tightened and oiled. needs an airbox or air cleaner and other misc items.


    • By mike rhoades
      View File Polaris 1996-1998 ATV Light Utility Service Manual
      Service manual for 1996-1998 Polaris ATVs and light utility vehicles covers: Magnum 2x4, Trail Blazer / Scrambler, Sportsman 4x4, Magnum 4x4, Trail Boss / Sport, 6x6 / Magnum 6x6,  Xplorer 300 / Xplorer 400, Sportsman 500 & Xpress 300 / Xpress 400
      Submitter mike rhoades Submitted 03/02/2019 Category Polaris ATV  
    • By mike rhoades
      Service manual for 1996-1998 Polaris ATVs and light utility vehicles covers: Magnum 2x4, Trail Blazer / Scrambler, Sportsman 4x4, Magnum 4x4, Trail Boss / Sport, 6x6 / Magnum 6x6,  Xplorer 300 / Xplorer 400, Sportsman 500 & Xpress 300 / Xpress 400
    • By colin james
      View File 1985-1995 Polaris ATV Service Manual
      This is the service manual for 1985-1995 Polaris ATVs. Download all the chapters for the complete manual. 
      Includes the following Polaris ATV models:
      Scrambler, Trail Boss, Cyclone, Big Boss, 250, 350, 400, Sportsman, Trail Blazer, Sport, & Magnum. 
      Submitter colin james Submitted 11/25/2018 Category Polaris ATV  
    • By colin james
      This is the service manual for 1985-1995 Polaris ATVs. Download all the chapters for the complete manual. 
      Includes the following Polaris ATV models:
      Scrambler, Trail Boss, Cyclone, Big Boss, 250, 350, 400, Sportsman, Trail Blazer, Sport, & Magnum. 
  • Recently Browsing   0 members

    No registered users viewing this page.


×
×
  • Create New...