Polaris carb problem (possibly)

[NavajoNPaleFace]

I have an '04 500 HO Sportsman Polaris with the Mikuni carb and with right at 1500 miles on it.

I've been having some problems with it that, even after four trips to a good and qualified Polaris mechanic, has yet been found and fixed.

On occassion the engine will cut out (spit and sputter) when going up a fairly steep incline.

I have to keep 'pumping' the throttle to keep it going yet it has stalled on a couple of climbs.

I've also noticed the same cutting out right after topping it off with fuel but after a few miles it seems to smooth out (until, possibly, that first steep hill comes along).

We thought that the filter screen where the fuel line is inserted in the tank was plugged or collapsed but that is not the case.

We thought that the gas from the main station I use might be bad so I tried three different brands of gasoline (from three separate stations, of course) and it cut out with all three brands.

The annoying thing is that it only acts this way on occassion but, yet, no one should expect anything less than a great running quad when it's new.

We thought that the jetting was set too rich since I can smell a strong odor of gasoline at times.

But, the jets have been checked out.  They reset the float and even tore the carb down and rebuilt it.  But the problem persists.

I have another appointment to drop it off next week and they are to get first hand guidance from Polaris on further attempts to repair it.

I ride with severeal other models of Polaris and no one else has encountered the problem.

The head mechanic at the dealership that is working on it is a really sharp guy who has had his share of years working on quads and the whole thing has him and his mechanics baffled.

I'm still thinking that the float needle valve is bad and/or worn and is letting too much gas into the bowl and, consequently, flooding out the carb.

The mechanics all have said they have checked that and found no problem.

My question is has anyone experienced any sort of problem such as I am and, if so, what the thoughts are as to the source of the problem(s).

Could some sort of electrical problem exist that might cause it and, if so, what might I look for?

Thanks for any help you might be able to give.

[264 WIN MAG]

Did you do the plug chop to check the jetting or did the factory. Often times if you ask them to do it and they know nothing has been changed they'll leave it alone. Most bikes come from the factory rich and mine was the same way. I brought it in and they said it was fine and then I did a chop and sure enough it was running rich. I changed the jet down and the thing purs like a kitten now.

Spittering and sputtering problems I have seen:
trash in carb
pinched or clogged vent hose on gas tank or carb
improper adjustment of idle mixture screw
float bowl jammed
fuel filter has trash in it
spark plug fouled

I don't know what to tell you, but from my experience if you are running fine most of the time and it just runs bad when you get on an incline or get the motor in a bind something is wrong with the jetting or there is trash in the carb.

What color is the spark plug?

[NavajoNPaleFace]

Thanks for the reply.

The jetting that was done was done by the shop.  

I didn't mention but they re-jetted the carb so that I could get an altitude range  of 2,000-6,000 feet.  However, this was done AFTER the initial cutting-out problem I encounter.

The spark plug I pulled out, as well as the one the mechanic pulled, was black but not from burning oil.

I pulled out the one in 'her' last evening and, it too, is black.

They claim to have checked the carb out well and, in fact I watched them, tear the carb down and rebuild it.

What are you referring to when you mention 'plug chop'?  I'm not aware of that term.

I'll check out the over-flow tube to see it it's pinched.

Otherwise, I'm lost for suggestions, myself.

The shop, whose mechanics are well-known in the area for their excellence are also at a lost.

Hopefully, this next 'leave' will give them time to really go over 'her' much more than the times they spent an hour or so looking at just the carb.

Again, thanks for taking the time and replying.

[264 WIN MAG]

As I suspected your problem is in the jetting. If you change altitude, air restriction, exhaust restriction, add aftermarket parts, etc. you are going to have to rejet.

Like I was saying before most bikes come with the same jetting across the board. The companies do not take into account your altitude and things like this. When I got mine from the factory the stock jet on a Grizzly is a 153.8 and I had to go down to a 145 because I was running too rich and having the same problems you are having right now. Although if I was to travel to where you are at I would have to rejet for the higher altitudes or the Grizzly would run like poop.

A plug chop is simple to do and you have already done it. Pull the plug and check the color. If the plug is black as it is in your case it means you are running to rich and need to go down on the size of the jet. If the plug is white you are running lean and you need to go up on the jet size. If the plug is a light brown color you are just right. Rich won’t hurt anything although the bike might run like poop under a bind because the carb is being flooded with too much fuel. Running lean on the other hand will cause excess heat in the engine and will eventually tear some stuff up and cause you major problems in the long run.

When you do the jetting just go down one size at a time until you find the perfect spot for you bike, and remember that all bikes are different and will have to be done uniquely.

[dcb]

I would try a hotter plug to see if that could be the problem? a sooty "bLAcK" plug can be a week spark.
 Also check make sure you are not plugging up the vent on the gas cap when you fill your tank, when going up in a steep angle the gas could be pluggin the vent.

[264 WIN MAG]

A hotter plug is not going to help. If the plug is black this means there is an excess of fuel. If the bike is new the plug should be fine. If the plug is fouled I would replace it, but not with a hotter plug because you might cause yourself to run lean. Like I said before you would much rather want to run rich than lean.

If the plug is black you are getting too much fuel so go down on the jet size some.

black=rich
white=lean
grey or light brown=perfect

Sometimes you also might have to mess with the idle mixture screw a tad bit from the factory. I know the settings for my bike at the altitude and mods where I am at, but I have no idea for a 500ho at your altitude and mods.

Just have to keep messing with it until you get it right.

[dcb]

It is possible that you could have an electrical problem. maybe? ask them how the coil checked out. it could be a week spark or bad spark plug wire.

The spark plug I pulled out, as well as the one the mechanic pulled, was black but not from burning oil.

I pulled out the one in 'her' last evening and, it too, is black
Symptoms
Soft, black, sooty, dry-looking deposits indicate a rich air-fuel mixture, weak ignition, or wrong heat range spark plug (too cold). This will result in engine misfire.

Recommendations
Check for correct plug heat range.  On carbureted vehicles, check choke and choke pulloff, high float level, and needle and seat condition.

 since the carb had been rebuilt the float set and probably a number of other checks, and the top notch polaris mechanic said there is no basis for the problem. ""  On carbureted vehicles, check choke and choke pulloff, high float level, and needle and seat condition"" it only seem right that you go back to the basics. replace the plug with  a higher heat range plug .
Try it and see. it will not cause the engine to run any richer.

Controlling the operating temperature of the plug’s firing tip is the single most important factor in spark plug design. “Heat range” is the relative temperature of the spark plug’s core nose, and it is determined by the length and diameter of the insulator tip, as well as the ability of the plug to transfer heat into the cooling system. A “cold” plug transfers heat rapidly from its firing end into the cooling system and is used to avoid core nose heat saturation where combustion-chamber or cylinder-head temperatures are relatively high. A “hot” plug has a slower heat transfer rate and is used to avoid fouling under relatively low chamber or head temperatures. What’s confusing is that a “hotter” (higher performance level) engine requires a colder plug because more power equals higher cylinder temperatures.