Newbie with 97 Polaris xpress 300 carb issues... Please help!!!!

[Louznmemind]

Howdy all, new to the forum, forums in general, and 2 strokes altogether. I have a new to me 97 Polaris Express 300, it has been bored .30 over, running 40.1 premix, oiler lines are blocked off. I admit my ignorance of 2 strokes and I'm Louznmemind with this thing.... I cannot get it to start without holding the throttle wide open and it will not idle on its own no matter what I do. Once I get it started I have to hold the throttle slightly open to keep it running, it will go into gear and SEEMS to run good all through the throttle range, it screams at WOT but when you let off it wants to bog out, it will keep running if you keep bumping the throttle. The carb has been taken apart and cleaned although it looked brand new inside when I took it apart. The main issue it had when I got it was it would pour gas out of the overflow as soon as you turned on the petcock, I replaced the petcock and adjusted the float height, I also replaced the float needle and seat but I'm not sure I have the float height correct. Is there a process to adjusting the float height considering it is made into the float bowl? Could this be my issue or should I also look elsewhere? I have tried adjusting the air screw to no avail, even at 1/8" intervals but the idle never changes at all, what is the default setting for this screw as well as the idle screw? I apologize if this is confusing or if I missed giving any necessary info but I will do my best to clear anything up if someone could please give me some advice. 

[Mech]

Well you need to know the fuel is fresh. Does it have compression ? It would be a good idea to recheck the carby's clean and adjusted right.

The idle mixture should change with a half turn of the screw, if it was doing nothing it sounds like it's jet or air bleed's  blocked.

There will be a workshop manual somewhere, probably in the downloads on this site. That will show you how to check the float level.

When you have the carby out, check the connection to the inlet manifold's airtight.

[Louznmemind]

Fuel was mixed by me and is fresh, also replaced Fuel lines, tank was empty when I got it. 

I have not checked compression but will definitely do that. 

I've checked the Intake connection and found no air leaks. I'll recheck the idle mixture screw because it's definitely not changing anything and I'll see if I can find the download for the float adjustment. Thank you, this thing is testing my patience. 

[Louznmemind]

Alright y'all, compression check shows 100 psi and it holds it. (tested with carb both on and off the machine) As mentioned, it has been bored .30 over, it was bored before I got it and supposedly didn't have a lot of ride time afterwards but I can't say how fresh it is. Seems it should be a bit higher from what I've researched but I really don't have a clue. As far as float adjustment info on this forum, I haven't found it yet but also haven't had a lot of time to look. As far as the jet needle, it appears to be factory 169 and is set on the 3rd slot from the top (as it was when I got the machine). Pilot jet is factory #40, and main jet is factory #155

[Mech]

Even if the float level is a bit out, the idle mixture should still adjust. I'm pretty sure you need to have another look in the carby, or manifold for leaks. It would be a good idea to check if it's got reed valves, that they are ok.

When you pull the carby apart blow through all the various drillings, especially the ones going to the idle mixture discharge holes. . Check the jets are clean, including the air jets just inside the air intake side of the venturi.

[Louznmemind]

Took the carb back apart today and literally cleaned every single piece and every passage, I'm more confident now than the first time I went through it. The pilot jet has a hair thin obstruction inside that would not come out, not exactly sure what it is but I replaced it with the new pilot jet. First time I did not take the slide apart and pull the jet needle, when I pulled it today I discovered the plastic washer under the clip was not there. I'm not sure what that affects exactly but I put the new one on it from the kit. Also found the new check valve on the carb overflow tube was clogged, is that check valve necessary? 

Is 100 psi acceptable on the compression test? As far as setting float level, I can't download any manuals until I get to 10 posts but I'm hoping I at least have it in the ballpark. I've checked and not found any manifold leaks. I'll be getting it ready to start in the morning and see what happens....

[jcyoungkeit]

I would check crankshaft seals also. could be pulling air in through them. I had a trailboss with a bad stator side seal that had similar symptoms. 

[Louznmemind]

I promise I'm not a mechanical moron but this thing....  

Thanks everyone for your input, I'll be using it all. Got carb back on this morning, no difference. 

Still starts only with throttle held wide open and will not idle. Pulled the crankcase drain bolt and drained about 3 bottle caps of gas. I left the drain bolt out and went to crank it just to see if everything drained, it started right up on its own and idled extremely low off just the gas in the carb bowl.

Put the drain plug back in, hooked up a fuel source, and again it would not start without holding the throttle wide open and would not idle. 

Pulled the drain plug again and got about a cap full of gas. The carb is also shooting a mist of gas out the back of the carb when I keep it running. 

 

 

[Mech]

A bit of a mist coming out of the carb is common, but it might be a sign of crook reed valves.

It sounds like it's flooding. You need to verify the float level. Some bikes you can attach a bit of clear plastic hose to the drain pipe, bend the pipe up the side of the carby, undo the drain screw and start the motor. The fuel level will be seen in the hose and it should be just slightly below the top of the bottom case/float chamber. Then I'd wind the idle mixture lean, lower the slide needle and see how it went. If it runs better then I'd adjust the idle mixture, then ride and test and adjust the slide needle or main jet.

[Louznmemind]

I appreciate the info, I should be able to mess with it again sometime tomorrow. 

This is the first time I've ever seen the floats made into the bowl and it's thrown me for a loop for whatever reason but I'm not giving up.

[spock58]

On 2/20/2022 at 8:03 AM, jcyoungkeit said:

I would check crankshaft seals also. could be pulling air in through them. I had a trailboss with a bad stator side seal that had similar symptoms. 

I agree with this possibility if the carb isn't the problem. Very common with older 2 strokes.

[Louznmemind]

I guess that's my next route, went through the carb again yesterday. I set the floats from what sparce info I could find on YouTube and still have the same issue. Definitely a learning experience...

[Mech]

I agree that crank seals can cause starting problems, but this thing sounds like a flooding problem. If the seals leak, don't they run lean ? This bike accumulates fuel in the crank. I've diagnosed and fixed leaking crank seals before, but I don't remember flooding being the problem..  Perhaps my memory's no good...  Was flooding a symptom when you guys found leaking crank seals ? Whether flooding is or isn't a symptom of seal wear, it would be something to check for hard starting.

Have you checked the choke is right off ? Does the choke plunger have it's rubber seat still ?

They can also get a distorted bore which buggers up the transfer ports operation.. That makes them hard to start. The way to check that is to pull the cylinder off, take the piston off, take the rings off and slide one down the bore. Then use the piston to push the ring down a little at a time, especially where the transfer ports are, and holding the cylinder up to the light you look for light between the ring and the cylinder wall.

 

[Louznmemind]

This thing is definitely testing my patience. It's definitely a flooding issue, if I drain the crankcase and leave the drain plug out, it starts first push of the button and idles just enough to keep it running for maybe 15 to 20 seconds. 

When I put the drain plug back in, it doesn't want to start and won't idle. When I take the drain plug right back out, it has gas in it again. 

Petcock is new and is working fine, it's only flooding when I try to start it and keep it running that it fills the crankcase. 

[spock58]

First thing with flooding that is suspected is the needle & seat - it could be the problem still. Since it was replaced, did you install a new gasket (or o-ring) on the seat?

It's important to get the proper size n&s since there are different styles/sizes available; gravity vs. fuel pump fed. 

[Mech]

If the choke is a plunger type, they only operate when the throttle is closed, or near closed. When the throttle's open they don't have enough vacuum to lift the fuel. I'd pull the plunger and check it's still got it's rubber seat/seal.

If you turn the fuel tap off and start it, what does it do ? If you turn the fuel on and off enough to keep the carby just full enough to run, does it still flood ?

[Mech]

Have you checked the float actually does float ?

As has been said, you need to be sure the float works and isn't leaking between the float needle seat and carby body. A simple test is to take the carby off and tip it up on it's side while you blow through the fuel inlet, then slowly tilt the carby till it's level and the needle should seal against your blowing. It should actually stop your blowing when the float starts dangling down against the needle, it doesn't have to be totally flat. If you tilt it so the float swings away from the needle, then swing it so the float will be dangling but against the needle, it should stop the flow then.  It's a good idea to do that test whenever you've had a carby apart. Sometimes the floats get jammed down by the needle dropping too far. Rare, but it does happen.

Edited February 23, 2022 by Mech

[Louznmemind]

2 hours ago, spock58 said:

First thing with flooding that is suspected is the needle & seat - it could be the problem still. Since it was replaced, did you install a new gasket (or o-ring) on the seat?

It's important to get the proper size n&s since there are different styles/sizes available; gravity vs. fuel pump fed. 

Considering this is the first carb of this type I have dealt with and the po obviously left at least one piece out, I'm not sure.

The seat I took out of it had a tiny rubber o ring that sealed(?) when it was threaded into the carb, it broke in half when I took it out, the new one has an equivalent size metal washer. I do know the needle and seat are identical to the ones that came out of it otherwise. 

The kit came with the machine and I just assumed it was correct. (Possibly a bad assumption?) 

 

 

[Louznmemind]

47 minutes ago, Mech said:

If the choke is a plunger type, they only operate when the throttle is closed, or near closed. When the throttle's open they don't have enough vacuum to lift the fuel. I'd pull the plunger and check it's still got it's rubber seat/seal.

If you turn the fuel tap off and start it, what does it do ? If you turn the fuel on and off enough to keep the carby just full enough to run, does it still flood ?

It is the plunger type, where exactly would the rubber seat/seal be? There's a plastic cylinder/plunger that goes into the choke hole, if you look down into the plunger hole there is nothing but a smaller hole in the bottom. 

I've not tried that process with the fuel valve so I'm not sure. 

[Louznmemind]

49 minutes ago, Mech said:

Have you checked the float actually does float ?

As has been said, you need to be sure the float works and isn't leaking between the float needle seat and carby body. A simple test is to take the carby off and tip it up on it's side while you blow through the fuel inlet, then slowly tilt the carby till it's level and the needle should seal against your blowing. It should actually stop your blowing when the float starts dangling down against the needle, it doesn't have to be totally flat. If you tilt it so the float swings away from the needle, then swing it so the float will be dangling but against the needle, it should stop the flow then.  It's a good idea to do that test whenever you've had a carby apart. Sometimes the floats get jammed down by the needle dropping too far. Rare, but it does happen.

Honestly the way you described it, I'm not positive. I do know the "floats" float with fuel in the bowl but are they actually raising the needle assembly when it's put together, again I can't say for sure.

I will check with the method you described. With all of y'alls responses I definitely feel like I'm narrowing things down. Much appreciated to you all..

[Mech]

Some old floats were hollow and could get cracks and not float, or not at the right height.

That metal washer under the float needle seat might not be sealing. If the surface was made to have a rubber ring it may not seal with the metal washer. It might be changing the float level too.

In most carbs the choke plunger is metal, and it has a rubber insert in the end to act as a seal when the choke's closed.

And definitely try managing the float level by turning the fuel tap on and off while it's running. Once the carby's full it should run for two minutes before it runs out. Try only opening the tap for a couple of seconds at a time and see if it will run and idle. If it does run pretty ok then, then you do have a float problem.

[Louznmemind]

The parts fiche for the Express 300 shows 2 different carbs, one shows a needle valve washer (part #3130047) and the other shows what they're calling a needle valve packing (part # 3130017)

Considering mine originally did not have the washer, I can only assume it takes the latter. I'm going to have to order one and wait forever for it but I'm hoping and praying that is my issue.

 

Edited February 24, 2022 by Louznmemind

[Louznmemind]

On 2/22/2022 at 11:03 PM, Mech said:

That metal washer under the float needle seat might not be sealing. If the surface was made to have a rubber ring it may not seal with the metal washer. It might be changing the float level too.

After this info as well as the info in the post Imade above this one, I took the carb back off this morning to compare the "packing" to the washer. 

It couldn't be more obvious, the hole that the needle seat screws into has a small groove inside that sits slightly lower than the outer ridge.

The washer sits on the outer ridge where as the packing should sit down inside on the groove. You can see the what I'm referring to in the pic. I'm 95% sure that is my issue. I feel like an idiot for not noticing this sooner.

Now I have to order a few so I have extras and wait 4 or 5 days for it. It seems it's not a typical "o ring" because even the ones that small seem thicker unless someone knows something else I don't..

[Mech]

A good engineering supply shop should be able to supply an O ring the right size. O rings come in different diameters and cross-section. Even the tiniest ones fitted to, for instance, the idle mixture screw, are standard sizes.

And good for you for finding it. When you put it together do that tilting test to make sure it's closing properly and sealing right off air-tight.

[Louznmemind]

Thanks Mech, I just went ahead and ordered a few OEM ones for the time being. Once I see exactly what they are maybe I can direct match them if the need ever arises.

I figure since the old one came out in pieces it would be hard to match anyhow. I may as well get what it calls for after all I've put myself through, lol.

I'm not counting my chickens until I get it back together but it makes sense to me now. I will definitely do the tilt test. 

Big thanks to everyone, I'll update when I get it back together.  Fingers crossed !!

[Louznmemind]

Well y'all, I feel like a complete idiot. I had the choke all out of whack and that was my issue the entire time.

I didn't realize the choke had a half setting and thought that was full choke, Long story short, it starts right up, idles good, and has about 60% less smoke from the exhaust. I ordered myself a dunce hat, it should be here tomorrow..

[Louznmemind]

This was a double post so I edited it out, I don't know how to remove it. Sorry

 

 

Edited March 5, 2022 by Louznmemind
Double posted

[Mech]

I'd leave the hat on the shelf for now.

It's possible you had two problems, which can really confuse the issue.

Well done for getting to the bottom of it.

[Louznmemind]

1 hour ago, Mech said:

I'd leave the hat on the shelf for now.

It's possible you had two problems, which can really confuse the issue.

Well done for getting to the bottom of it.

Lol..  I'm definitely not counting my chickens yet but it's doing very well at the moment. 

Still have a list of things to do to it otherwise but it's running and idling very well. I finally got to ride it for the first time without it bogging or quitting.

Credit goes to this forum and those that replied, it was the service manual download that finally set everything in. I've certainly learned a lot but have much more to learn. The flooding issue, which has tested me for an unacceptable amount of time is solved though. 

I'm sure I'll be making separate posts with questions on other topics but maybe this thread will help someone like me someday. 

[Curtis Underwood]

I have worked on so many of these carbs it is not even funny.
There is a list of things that I go by to find the and fix the issue.
1. Clean the carb
2. Check for air leaks at intake manifold (if it is rubber metal ended, found a lot of them that you cannot see unless you slightly twist the manifold and then you will see crack if it has one)
3. Float valve
4. Ignition system
5. Air filter system (has to have the air filter in place for carb to function correctly).
6. Check engine valves clearances both intake and exhaust 
7. Check compression

Your problem sound to me like you have a faulty float valve or the Oring under the valve seat is leaking by. The easiest way to find out is with the carb off. Hook the fuel line up. Hold the carb level and turn the petcock on.
Hold it in the level position for at least two minutes. If any fuel comes out of carb, then the float is leaking by.
As to the fuel blow back when the carb is on without the air filter on it you will have some at full throttle but should not have any at mid throttle. This indicate the fuel mixture is a little too rich, but I have found on some carbs the machine will not run at full RPM without having a little.
I do not rebuild any carb that has a float valve problem. The main reason is the rebuild kits are not specifically for that carb. They are always for several different carbs and says they will work on that machine. But I have found they are not exact. Best to buy new carb from OEM for the machine. I know the OEM are more expensive but you get what you pay for. I think I went through buying about 3 carbs for my Yamaha before biting the bullet and getting one from Yamaha. The ones they sell online for cheap price most likely will not be setup for your machine. If you notice in what they will fit is a range of different size machines.