Carb issues help?
I just rebuilt the carb on my '04 Magnum 330. It's a Mikuni 34mm CV carb.

I got the rebuild kit from my local Polaris dealer. I also got 8' of 1/4" fuel line and a new in-line filter. I drained/cleaned the fuel tank and the fuel is now for the lawn mower. All of the fuel lines were replaced from the tank to the petcock, to the fuel pump, and to the carb. I even replaced the vacuum line from the carb to the fuel pump. New in-line filters installed. Fresh fuel in the tank.

The carb kit had replacement parts for everything except the pilot screw/needle. I checked the float settings when I rebuilt it. I clipped the needle at 3 of 5, just like when I tore it down (factory setting). I cleaned the pilot screw, and reinstalled to two turns out from bottom.

I was able to get it started w/o any problems, and it idles perfect (got lucky). But I haven't adjusted the pilot screw.

Now my problem. I start up, closed the choke, and idles fine. BUT, if I try to give it gas it starts to stumble. I tried to give it wide open throttle, and it died. I can restart it and it runs fine at idle. I haven't tried driving it yet since I still have the front end tore apart.

Any thoughts? I can get to the needle easy enough, but it's clipped at the same setting as I tore it apart at, and where it's been running fine since I bought it.

Thanks in advance,
Wayne
St Louis, MO

 

2 to 2 1/2 turns is good on the fuel/air screw as most times from the factory these are set very lean. After removing the block off plug I've even found a couple at 1/2 turn out and one almost closed that was a set this way from the factory.The owner had a heck of a time starting this up and had to run with the choke open for a good while. If you sure the jets are clean and clear, enough fuel is getting to the carb (you can pull the line and it should pulse a good fuel flow while cranking), Then I'd check the jet needle and see if it's installed right, that the spring is holding it down and it's not moving up the slide.I've seen this happen to where the slide would move a little,but not the needle and would bog or the needle would move up in the slide! OPT

 

Thanks for replying. I have enough experience dealing with holley's and rochester q-jets for cars, but this single thing is just boggling my mind. The only single carb I have is for my lawn mower, and this isn't even close. So I guess I'm asking for a little help and talk me through this. So thanks in advance.

I will address your reply as best I can. As far as fuel goes, I went back to my car roots and installed a clear in-line fuel filter that I got at my Polaris dealer. He tried to talk me into a factory filter for cheaper, but I wanted to 'see' that my fuel was flowing (and it is).

My pilot screw plug had been removed prior to my tear down. I had bought my bike from a Polaris mechanic in southern IL 3 years ago. So it had been rebuilt before. I just don't know who or how long ago. When I rebuilt it from the kit, I found an extra screw on the table. When I researched it I realized that it was the pilot screw and I didn't count my turns. When I rebuilt it, I called my dealer and asked the service guys and they said to start at 2 turns. So I gently bottomed it and backed it out two full turns. I can go to 2 1/2 or 3, if that's what I need to do. But before I do, should I back the idle **** on the bottom of the carb, that goes to the throttle cable?

I replaced the needle in the middle of the slide/diaphram with a new needle in the rebuild kit. Not the seat, just the needle. I put the clip in the middle slot (3 of 5), where it was set on the tear down (and had been working fine for the last three years).

Should I open it back up and check to make sure that it's moving and maybe stretch the spring a little to give it more tension? (since I don't have a replacement and it did not come in the kit and by the way, it didn't have a replacement diaphram, but it looked to be in good shape and not dry rotted or cracked).

I can start it normally now, choke closed when cold (**** pulled out), give it a minute and open the choke (**** pushed in), and it will idle. I do have the idle **** on the bottom of the carb turned in a little. But when I give it any gas, it bogs down/stumbles and then dies. Hit the key and it'll start right back up, but hit the gas and I can only repeat the above.

I know that I'm rambling a bit, but I want to give you a full picture of where I'm at, so I'm coloring inside the lines for you.

Thanks again for your help,
Wayne
St Louis, MO

 

The idle setting shouldn't be problem,you can adjust it after you find the source of the bogging. Look at the carb on your model here and see if it might help you,especially on the slide needle and parts. Browse OPT

 

Thanks again.

I didn't remove the butterfly, I cleaned around it.

I wasn't able to remove the black plastic 'jet assembly', because of the security bolts holding them in place. I also wasn't able to remove the 'jet needle' as well. So I only soaked the entire body with these parts in place. I reassembled it in reverse, replacing those parts that came in the kit. As best that I can see, I reassembled it exactly as I see in the diagram for 2004 Magnum 4x4 carb.

I will pull the top off, pull the slide/diaphram, and put a little carb cleaner into the 'jet needle', and let it soak. I will also turn the pilot screw another 1/2 turn.

Can you suggest any other ideas?

Thanks,
Wayne

 

Be careful with carb cleaner on the plastic parts,plus have you replaced or cleaned the air filter and prefilter? If dirty could be the problem or part of it. OPT

 

I have had a few that i had to adjust the throttle for this problem.

 

sounds like you may still have some crap in the carb

 

Guys, I have the same problem as Wayne on my 2003 Trail Boss 330. I bought it used after it sat up for two years. It has the same CV carb. I pull the carb off, soaked and cleaned it. I'm certain it is assembled correctly. It started right up afterward and idled great. But at 1/4 throttle it began to run rough and at 1/2 throttle or more it seemed like it was starved for gas and died out. I pulled it again, cleaned it again with the same results. I've clean that carburetor once a day for four days. Nothing changes. I'm pretty sure its not dirt or gum anymore. My main jet was stripped so I couldn't get it out but I cleaned it well. I can fill the tube the jet screws into with gas and it runs out through the carb with no problems. I cleaned - not replaced - the needle jet and the jet needle. The pilot jet is at 2 turns. ( thanks to this forum!) I went through the fuel pump today. Just cleaning it and the lines - I didn't have a kit. same results. I've run it with the airbox on, off, with the two vent lines hooked to the airbox and without them hooked up. no changes... The needle jet looks good. The jet needle looks ok. The spring and diaphragm assembly works. I should mention that 2 days ago after cleaning it, it ran great! I rode it for about a 1/4 mile through all speed ranges and it ran really good. I pulled it in the shop, started put things back together and thought I'd like to hear it run one more time before I quit for the day. It started right up, idled great but for some reason, would not run past 1/4 throttle just as before. What am I missing? Just to be certain, those two vent tubes in the top rear of the carb are supposed to go to the airbox..... aren't they? Thanks

 

Have you checked for vacum leaks ?