Bought this machine not running. I've cleaned what seems to be a million carbs and feel very familiar with them. This 2001 Polaris Trail Boss 325 has got me stumped though.

All jets and passageways are clean.

When stone cold (as in sat all night long) and I try to start it, it will half-a$$ crank for about a second and die. First instinct is to pull the choke and it may do the same thing Half a$$ crank and die. Then the next time you try to start it, no matter what you do, it just cranks..and cranks...and cranks etc.

When this condition exists, I turned bowl drain screw and fuel came out. I can also verify that it has fuel in the carb just by the 10 times I have been in it and there is plenty of fuel in the bowl.

Spark is fantastic.

I can make it run by giving it a shot of go go juice and once you get it running, it runs, idles, fires excellent. Don't even have to hit the gas. Just tap the starter button and it purrs like a kitten and runs like it should. Once you are at this point, if you pull the choke the engine revs high like you would expect thus verifying that the choke is in fact working. Just has no affect when stone cold.

Note that the parts fisch shows a 145 main but I can tell you that the 120 in it is the correct jet. Hunted down and installed a 145 only to learn that it won't run on a 145...That's just a side note for anyone else doing a search wondering why they have a 120 when the fisch says it should be a 145.

The fact that I can get it running with carb cleaner tells me that it is in fact starving for fuel. But there's fuel in the bowl....so this tells me its gotta be some kind of a vacuum leak. Intake book looks great and I see no issues with it.

Also realized that these things will not run right with air lid removed. It has a shorter style air filter on it and at first I thought someone must have put the wrong filter on it since the fisch shows the Polaris long style filter. then I accidentally looked at the 2002 specs and it shows a short style one that looks just like what is on my 2001 model machine. So I am thinking it is ok and just a fluke that it has the short style filter on it.

Checked valve clearance and all looked good.

Will check vacuum line running from carb to fuel pump tonight and really hope I find a big crack in it or something but I have glanced at it each of the 10 times I have had this carb off and don't see anything obvious.

On the contrary, how would I have fuel in the bowl if that line had a crack? Gravity?

So to my question, I feel this fuel pump is a pulse style pump. If I put my vacuum pump on it, it should simply hold vacuum and any indication otherwise would indicate a bad pump, correct?

Also this thing does one other weird thing:

You know how when an engine cranks, if you hold the throttle wide open the sound of the cranking engine changes? Well this will make that change just from me opening the choke wide open. That does not seem right to me. I can't think of a single other machine that has ever done this.

The entire choke system seems unusual. When you have the slide cover off the top of the carb, you can see the choke actually move when you pull and push the lever. Shouldn't that entire section under the rubber slide diaphragm be sealed in order for the slide to function? I am assuming the jet in here is used to make that slide work. Someone was clearly in here before I got the machine.

 

Have you checked the carb boots for cracks?

 

yes, it looks good. In thinking about this I am wondering If there is too much clearance in the CV slide.

The fact that pulling the choke will sometimes make it sound as if you are cranking with the throttle wide open tells me that its getting air from somewhere and that's the only place where the choke could air from. This could also explain why it won't run right with the lid off. Once warm, with the lid off it will only run up to about half its RPM range and then kind crackles and pops. Put the lid on and it will run through the entire RPM range like it should. Again, must not be able to get the proper suction it needs. I need to look and see if under these conditions that maybe the slide is not able to go all the way up. Haven't checked this yet.

Grasping at straws as this point.

 

A lot of the early 325 and some of the 330 machines were set way to lean from the factory. Same as with the Sportsman 500 you have to have the filter and air box on along with the lid to get them to run properly. I had several come into the shop for cold start problems and having to keep the choke on for an extended time. Some even had to drive off with the choke partially on until it warmed up. Once warm,they usually ran ok. What I found on the worst ones is that the fuel screw under the block off plug was way off. Found several that were only 1/2 turn out and the worst one that came in,the fuel screw was completely tuned in. Remove the plug and set the fuel screw to 2 to 2.5 turns and hopefully you'll see a difference on starting,warming up and idling. Several of the ones I changed needed the choke only for a little bit on cold days after that. Just a mistake from the Mikuni factory that Polaris didn't check.

 

My thinking is now definitely in this cv slide. When i came home i put a piece of foam in the end of the air filter lid neck and lo and behold it fired right off. Definitely a vacuum i am just amazed at this cv set up. Look at the attached pic showing the slide cavity. The hole you see in the 1 o clock position is the choke plunger with the choke fully turned on. The brass piece you see at 10 o clock position is the 175 air jet.

Is that hole supposed to be there? Mind you someone has been in here before. When i first got here the spring was off to the side where they had not put it together right.

Does this CV actually work by pressurizing the CV cavity to make the slide go up?

Seems to me with that hole at 1 o clock when you pull choke its simply going to suck air from cavity into choke stream which would cause the thing about full choke sounding like crank with throttle open.

The slide has slop but no worse than others ive seen.

 

Their pics function isnt working so copy and paste this url:

http://www.buggymasters.com/files/pics/image.jpg

 

Found the manual and it explains how the system works. Slide would not cause this problem. Atmospheric is in the chamber and that hole is supposed to be there.

Could this be as simple as the wrong air cleaner?

The parts fisch shows the old long style air cleaner. This one has the short style one that you see in the fisch for 2002 and up models. Local dealer has the correct one in stock. Going to get it tomorrow and see what happens. If its just the air cleaner I think I'll just bang my head against the wall a few times in disbelief.

 

Dont think air cleaner is the problem. This shorter filter is what is correct. Longer filter goes on but lid wont with longer filter. Parts fisch is wrong on this too.

 

Well looks like maybe i just burnt myself out on it. Pretty sure when i cleaned out the choke circuit i must not have pulled it out all the way when i hit it with air. Pulled top off carb, verified choke open and hit it again and had very good air going through it this time. Put it back together and ut fired right off. The clue was the engine sound when cranking with choke on. Passage had trash so the next best place to suck something through was the air jet. All good.

 

Good to hear it's running right.

I had a 2000 325 trail boss. Like OPT said, these motors are very cold natured. Don't be surprised if you have to let it sit for a bit to get it warmed up.