2001 Polaris Trail Boss 325- I did use th esearch function multipl times with different terms and found nothing that appeared as this same problem. Neighbor brought the machine to me for a tune up, wouldn't start when I got it but ran good last year, here's what I've done so far: Removed and cleaned the carb, removed and blew carb cleaner and air thru all jets and orifices, replaced bowl gasket. Owner said she put fresh fuel in the tank, but I still drained, rinsed, and refilled the tank with fresh fuel. Disconnected all fuel lines and blasted thru them with carb cleaner and air to remove all old fuel and any potential crap that may have been in there. Got it running, but it didn't want to stay idling. I tried adjusting the idle speed screw and even tho I screwed it in to the point the engine should have been screaming, it still wouldn't idle without me using the throttle. So I started diagnosing fuel flow: I had a steady stream of fuel to the pump I had a steady stream of fuel to the carb (no pulsing) I had vacuum at the fitting on the carb and also at the end of the vacuum hose at the pump. So just out of curiosity, I fired the machine up with the vacuum line disconnected at the carb. The machine idled high due to my previous adjustment, so I readjusted the idle. Idled great and had the proper throttle response when I punched the throttle. Then I went to reattach the vacuum line to the carb and the machine went back to idling down until it died. I repeated unhooking/hooking up the vacuum line and reattaching it to verify and had the same results. I removed the fuel pump and took off the top cover and drained the fuel out of the pump. All the fuel that came out was fresh fuel. The main diaphram looked good, with no cracks or breaks. Since all the fuel that came out was clean and there was no debris in the pump, I did not separate the middle and bottom compartments. Reinstalled the fuel pump, started the machine back up and had the same results as above: Remove the vacuum line from the carb and the machine seems to run great, reattach the line and it idles down gradually until it dies. I am going to double check the carb later today, but does anyone have any other ideas as to what may be the problem? Thanks In Advance for your help!!

 

As long as you haven't crossed the vacuum line with the fuel inlet line,the throttle slack is good (1/8" slack at the thumb throttle) but still dies when you install the vacuum line back up,then sounds like you have a restriction either in the fuel pump,the pump vacuum line itself can be leaking fuel(have had that happen before when a diaphragm seeped) or you may have some small blockage in the vacuum inlet of the carb itself. Fuel air screw should normally be between 2 to 2 1/2 turns out from a lightly seated position. PLUS make sure you haven't broken the small tip on the fuel air screw,partially blocking the idle circuit or the carb is ruined! Have had people do this before.

 

Thanks OPT!! I tagged the fuel/pulse lines before removal to be sure I didn't mix them up. I am going to go thru the carb a second time and also blow all the fuel lines out a second time just to be sure. I'll post my results a little later today.

 

Hi OPT, I dropped the ball on this, got sidetracked. Sorry bout that. I did a little more testing and found that I have vacuum at the carb fitting and also at the fuel pump end of the pulse hose. I decided to disassemble the pump to see if the blockage was there, But I found nothing and everything looked good. Since the price difference between the gasket set and a new pump was minimal, and I got a complete new pump, I ordered a pump. Hopefully the pump will arrive in a couple days. I will post my results after installing the new fuel pump. When the machine is running, should the fuel be pulsing out of the line at the carb or just flowing in a solid stream? Seems to me it should be pulsing and this machine is giving me a even stream..

 

Pumps are different on each machine depending on engine vacuum. Some will have a noticeable pulse of fuel,while others will just have a steady stream for the most part.As long as it's continuous is all that matters.

 

OK Thanks for the info, that helps. I'll post results when the pump gets here.

 

OK, new fuel pump increased fuel flow and machine starts and idles nice. Idle mixture screw is two turns out. Starting at mid throttle it starts missing/bogging. I did replace the spark plug boot with a brand new NGK boot, so I need to consider that. I also replaced the filthy stock air filter with a new UNI air filter. I'm going to try adjusting the needle first and see if that improves anything, if not I may have to buy a Polaris plug boot and try that. I hate getting a machine to work on when I can't run it first to assess the symptoms.

 

Sounds like you're getting close. You can try rising the needle,but sounds like it's still restricting,either still some trash/dirt in the carb? Another thing you can try is unplugging the black wire from the reverse limiter. Could be the source of the problem on the missing,cutting out at higher speed. Part #18. Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse

 

I changed my plan of attack:Pulled the carb again, just to verify proper stock jet sizes, and they are as listed in my manual. Carb is clean as a whistle. I'll try the reverse limiter first tomorrow after work since it's easier to verify/eliminate as a problem, I had that happen on my 91 350L, so I know what you are talking about with that. If the limiter doesn't change things, Ill try adjusting the needle.

 

Alright, here's more results: Unplugged black wire from reverse limiter: no change. Ran the clip up and down all 5 slots on the needle. No change other than a bit more rich on the bottom slot. Checked one ignition part (can't remember which it was right now, white/red wire to white wire) but it was supposed to have 250 ohms and did, so good there. Going to borrow a known good CDI from a buddy's machine tomorrow and try that.