1997 Polaris xplorer 500 bogging and popping out of carb

[spr203]

hello, 

i have a 1997 500 xplorer . 

it will ideal fine you go wide open and its lazy and spiting fuel out of carb. 

if i install the air box it runs worse . 

things that have been checked or replaced 

cam is in new condition 

valves adjusted 

carb replaced 

new gas 

fuel lines cleaned out 

new coil and plug 

seems like the ignition timing is retarded 

sometimes its hard to start 

any help would be great . 

thanks 

 

[Curtis Underwood]

First question did you buy new carb from OEM or just one off ebay that is a replacement?
If it is just one off ebay then lower or raise the needle by one notch this sets the air/fuel mixture. The repacements carbs that are no OEM are sold for machines that  vary in size. I bought one for a 450 cc and it said it fit 250cc through 650. It did same thing as you discribe so I justed the needle in the carb up and down until I found best running position. But carb never ran perfect on that machine, So put it on a 350 machine and it ran great, so I went back and bought OEM and it fixed problem.
Second thing that does cause this is the rubber intaker manifold beteween carburetor and head. If it has a air leak it can cause this to happen. They often crack and the crack is hard to see, slightly twisting them some times show the crack.
Even if the valves are adjusted to specs sometimes you have to losen them by a thousandth. The valve specs give a range adjust to highest of the range on the intake. Also if the valves are sticking and not moving open and closed freely it can cause this. Any valve problem can cause it to act like the timing is off. Next check to make sure it is in Time. The air cleaner has to be on these small engine for them to run properly.

[spr203]

thanks for your input . i will pull the rubber adapter off and check it . i have been moving the c clip up and down . 

 

[Curtis Underwood]

The problem with these carburators you get as replacement is they are set for a certain machine size and if you use them on a larger or smaller machine they have to be reset. I have used these and on a couple of machines not been able to get them to adjust to where machine would run good. but I was able to get the backfiring/popping/blowback to stop just could not get full power at same time. It could be it is just the carb with something that will not let it work on your machine.
If there is not an air leak I suspect since you have changed the c clip settings with little change in blow back that you have a valve sticking problem or a vlave that is not closing all the way.  When the cylinder comes up on compression stroke if the intake valve leaks by it will cause blow back and you will have that backfire popping sound.
I worked on a Honda 650 (now it was not a two cycle engine) but it had this backfiring or popping/blow back problem. I tried everything from a new carb (OEM to new igintion modules, coils, plugs etc.) Then someone metioned valves again and I had set them but I went back and did a check and found the intake valve was sticking and not closing all the way. I took a hammer handle pust valve in to force it to open and release it and watched it as it closed. It did not just spring back fast it close but seamed slower. So I pulled the heads and removed the valves. I found carbon build up on valve stims causing the valves to bind(almost did not get them out of head because of the build up). I cleaned the stims and bushings in the head, ground the valves and put new set of seals on it. Then because I had it tore down I went ahead and replaced the piston rings. I put it all back together and made sure timing was on, valves were set to specs, and it started and ran perfect. So your valves sounds like they may be sticking or maybe even have a burnt valve.

 

[Mech]

If it idles fine it won't be a valve problem.

It sounds to me like it's not getting enough fuel. Either that or the exhaust is blocked.

As has been said, aftermarket carbys are not set up for any particular market or altitude or fuel grade, they all need adjusting. I mostly take all the old jets out of the old carby and fit them to the new carby, slide needle and discharge jet included.

Before you do that though, (because this is easiest, but you don't mention having done it), you should check there is plenty of fuel getting to the carby by disconnecting the hose from the carby and running the pump if it has one.

[Curtis Underwood]

That machine I told you about that had a valve problem idled good but because of the valves were sticky, when it was revved up it would blow back and had a loss of power.
 Without being there there is no real way to tell. All we can do is to tell you what we have run up on.
Since Mech  said to check to see if enough fuel is getting to carb then the best way is to put a clear plastic hose on the overflow line and open the drain plug some. Hold the plastic hose up along side of he carb and if the fuel comes up to where the bowl meets the carb then the float is set right and you have plenty of fuel getting to the carb.

As Mech said if it is an after market carb it could very well be the jet sizes. Take the jets out of your old carb and get a set of torch tip cleaners (start with the smallest tip cleaner and go up in sizes until you get one that will not fit threw the jet) and this is to make sure it has no build up in them. This is only way I have found to make sure a jet is fully open. Then set the c clip to the same point as the c clip is set on the old carb needle. I have found in most cases the needles are the same lenght and size as the original.

[Mech]

What Curtis is showing there is a good way to check the float height, but it doesn't guarantee that there is enough flow of fuel to keep the bowl full once you open the throttle.. You need to disconnect the fuel hose from the carby and lay it sideways into a bottle, then either turn the tap on or start the engine so the pump operates, and check the fuel is flowing out of the hose at the full diameter of the hose. It's a good idea to check there is a good flow of fuel when you open the throttle too if it has a vacuum operated fuel pump. Start the motor, hop on and lock the brakes, put it in gear and give it about half throttle so it's starting to load up a bit.. the fuel should still flow out of the fuel hose at full diameter, if it doesn't, you may have a weak vacuum or a crook pump.

[Curtis Underwood]

We most of the time think that this is going to be one problem when it can very well be a combination of problems. I had a 350 yamaha come in several years ago. It would not start. So I used some starting fluid and it ran for a few seconds. This told me it was a carb or fuel issue. I cleaned the carburetor, replaced the fuel filter, and drained and cleaned the tank. It started up and idled good but blew back and back fired or popped. I found the timing chain off by one knotch on this machine that was causing the problem too. So you could have several issues at the same time causing this. It is not very often that you have multible issues causing same problem but it happens.
Mech way is a good way to check flow from pump. But if you have a full bowl using the check I showed (if the bowl is full when you start the engine and revve it as soon as it starts it should revve correctly until the fuel in the bowl is used) if it does not rev up to full rpm then it is not fuel flow problem. He also had a another good thought and that was the exaust system is blocked. The muffler can build up with carbon and stop up. Some mufflers have a tube with holes in it that the exuast passes through and these can stop up with carbon.
What we have not metioned is fuel filters. Some fuel systems have a filter or screen in them at a on/off fuel valve in the tank which valve has to be removed to clean or replace, an inline filter or on the carb that has a valve built into it with a filter. If you do not get good flow replace the filter or clean it. Filters can restrict the flow to a point that it will not run at high RPM after a short time. 
From what you have said I do not think it is a fuel flow problem.
What I think is it is going to end up being is either as Mech said the jets in the carb is the wrong size , the intake rubber adapter from head to carb has a leak, the carb has some tube where fuel flows that has stopped up, intake or exaust valves leaking by or low compression. 
The problem is we are not there and can only guess and say what we have run upon.

[Mech]

Yup, there are several things, or combinations of things that could cause it...

So, Spr, in the thread title it says "popping" out the carby and then you describe it as "spitting fuel" out the carby.

If it's just spitting fuel then it could be a blocked exhaust, not enough clearance on the inlet valve adjustment, worn cam bearings or a mistimed cam.

If it's backfiring out the carby(with a flame/loud pop), then it could be all sorts of things either fuel, electrical or mechanical..

At the moment to me it sounds as if the mixture is too lean, which causes it too burn too slowly, and so have lingering pockets of flame when the inlet valve starts to open.. And those lingering pockets of flame, ignite the incoming mixture every so often giving that "pop"...  And yes, all this happens even despite the exhaust stroke having supposedly swept the cylinder clean. Flame can "hide" up the spark-plug or in the corner between the valve and the head.

The changed carby could cause all this. If installing and disconnecting the air-box makes a big difference, then it points to the carby operation, not electrical or mechanical. Since it's simpler and cheaper than fitting new parts, you really need to make sure the new carby is set up for your bike, and the local altitude, temperatures and fuel grade. The simplest way for you to do that, if the replacement carby is an identical design as the original, is to change all the jets and needle and discharge tube which the slide needle drops into. 

If the new carby isn't identical then you need to first clean and adjust the carby, then set it up with the air-box and filter, then diagnose speed range and which jets or adjustments need to be made. You tune the idle jets and mixture and speed, which in your case souds about right already, then you adjust the main jet so it has fuel right to full power, you figure this by reading the spark-lug after taking it for a short full throttle blast, then after that you adjust the needle slide.   Get the carby right and I'll bet your problem will be fixed.. 

Oh, and Spr.. it would be a probably help if you told us the history, how long you've known the bike, what the original problem was, when and under what circumstances it arose,  what you did first, how the work has unfolded.. 

[Curtis Underwood]

Mech I agree with you we need the history of the machine it will tell us a lot. I agree it could be to lean of a mixture. But from experience I don't think it is with him saying he has moved the c-clip. Moving the clip to a notch above moves the needle down which give it less fuel and moving the clip to a notch below moves the needle up which makes it richer. So sounds like he has tried doing both with no or little effect. It could be just a bad carb too that has something wrong from the factory.
 

On 4/19/2022 at 8:16 PM, spr203 said:

thanks for your input . i will pull the rubber adapter off and check it . i have been moving the c clip up and down . 

 

 

[Curtis Underwood]

Mech you might be interested in what I meant to say and did not because I got side tracked about then by my wife lol, it was in the comment I made with the picture showing the setting of the float by use of a clear tube. That you can leave the drain open and actually see the fuel level in the tube that represents the level in the bowl with machine running. What I usually do is put a clear hose on and use a wire tie on tube to make it so it stays in the rasied position and check the float level then I start the machine and watch the level in the tube if running at full rpm it does not drop lower than about 1/8 to 1/4 inch then all is well with the float and fuel supply. I got this from some manual or from someone online don't remember which and it said that it could be used to see the level while machine is running.

[spr203]

thnaks guys . i will working on this tommorow night . i will update you . 

so these things will block the muffler up ?

 

[Mech]

Yeah that hose into the float bowl to check the float level has been used for half a century or more by mechanics.. I've been using it for more than a half century..  haha. It's a toss up whether it's best to check for fuel flow right through the carby first, or whether it's best to check it's getting to the carby as a first step. Either way we have to go on and continue looking for good flow or blockages if there is anything not right.

I always suggest to people that they do the easy things first, (even if the easy thing seems unlikely, it's best to eliminate it before going for the complex stuff). Mostly, even on the side of the track, we can pull the fuel hose off and check for fuel. It's the "simple" that people need to have in their mind when they do find themselves broken down and wondering what to do.

And... for Spr or anyone else reading this that is not used to diagnosis.. when  we diagnose things there are two things we need to consider, the symptoms, and the circumstances.. If someone says their car makes a rumbling noise it means nearly nothing, it's just a symptom alone, but if they say it makes a rumbling noise when they go around corners, it tells a whole lot more, and if they say it's only doing it around left hand corners, then it's getting real clear what things we should be looking at. If a bike stops running at the track, that is an entirely different scenario to a bike that has sat for a week and now won't start, or a bike that sat in a shed for ten years and now won't start. So we need to know if it manifests the problem hot, cold, after a long sit, after a long or short ride, cornering, decelerating or braking, when it's wet, at part throttle or full throttle. . As far as symptoms go, we need to look for every symptom our senses can detect, visual symptoms, sound, smell, vibration or heat, even sometimes a taste we get in our mouth from certain  things (no, don't go tasting things). Every symptom, and every circumstance can help diagnose a problem, and if we look really diligently for a symptom or a circumstance and it's not there, that allows us to ascertain the problem through a process of elimination.. The symptom or condition that's not manifesting can rule some things out.

That's why we need the full history Spr.. Haha.

[Mech]

Suzuki quads have a bung at the back of the muffler and it's part of suzuki routine service to take the bung out and start the motor.. But you know, in forty years of servicing suzuki, I've never seen a blocked muffler, not unless it was a blown motor and the muffler was full of oil. On various bits of machinery though, and vehicles, I've seen blocked mufflers, and it causes spitting out the inlet and bogging down as the revs build. The usual way to diagnose it is to attach a vacuum gauge and rev the engine on the spot. If the mufflers blocked the vacuum drops steadily away as the revs rise.