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Discussion Starter #1 (Edited)
Hello everybody,just bought my first ATV 4 months ago, Having an issue with it. I will try to give you every possible detail.
Its a 2006 AC 500 FIS, Dont know if it matters but just took it to NH for a 50 miles ride 1ST ride,Seemed fine,Gradual throttle it ran very well. I havnt really snapped open the throttle since i got it. I opened it up fully the other day,It "Backfires" not 1 loud bang but lots of little bangs and pops,its all broken up sounding "Loss of top end power" it doesn't want to die but it wont accelerate any faster. I dont remember it doing it this bad when i got it.. I have all the plastics off right now and have been trying everything. I cleaned the carb out with air and cleaner, The needle valve I believe? It has a small rubber cone tip. It had alot of play maybe a few mm, I dont know if this is normal,wouldnt pull up much,as to say it wasnt freely moving up out of its hole,measured from lip on carb body to top of float when lightly touching the needle, it was apx 17mm. I checked the plug gap 28-32, valves seemed correct,if you think this could be a definate cause of this issue i will measure again, it was complicated for me to do it (1st time) so not 100% that measurement is correct or if it was perfectly at TDC, The spark plug looks perfect to me,brown electrode with black on base of thread case, and it was dry, Some new items are sparkplug,oil and air filter,oil,fuel filter. I just cleaned v belt housing on pass side,looked fine not worn, I think the spark is weak,its not a nice blue arc jumping a 1/4 inch its yellowish orange and doesnt jump to well.. 16.32k ohms from inside plug boot to ign coil. Read 1.5 ish on just ign coil,by coil i mean the box the sparkplug wire comes from. I cut 1/2" off boot cable and screwed boot back on,no difference, I run 93 Octane with seafoam. I recently cleaned and dielectric greased all accessible plugs cdi speedo everything i could get to,some were filthy, this was b4 this problem. I tried unhooking connections 1 at a time and then riding,didnt help. Everything is stock on the atv,dont know if it matters but 2 weeks ago some fuse went and need to pull brake to start now, Maybe this is a clue?No idea. I thought for sure I figured it out when I pulled fuel filter out, blew into the top of it and it was pretty tough, its brand new though, i blew some air gently through it, 10 times easier,siphoned some debris out of tank, i was sure this was it, no difference at all, I could go on and on. Thats the problem. I have read litterally hundreds of posts in here and elsewhere. i know alot you you really know your stuff so any help would be hugely appreciated. Thanks for your time all.
 

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welcome to the site but please no capslock its hard on the eyes
 

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Yeah please no more capslock!

Okay, your new air filter was this before or after the problem started? If you replaced it with a high flow air filter you could be leaning the mixture out.

If your weather has had a drastic change this could contribute to it if the bike was close to being lean or rich. As the air becomes colder it also becomes more dense leaning the air fuel mixture out. Warmer temps should cause the mixture to richen.

Your symptoms sound like you could possibly be running lean as a lean condition will cause backfiring and a noticable lack of power.

You are running with your airbox lid on trying to figure this out correct? If your airbox lid is off it will cause you to lean out your mixture as well. Check your carb to intake boot, carb to airbox boots for cracks & tears, you can also use a little starting fluid to check for air leaks. With the engine idling spray the area around the carb and boots, if the engine picks up rpm you should look for a leak.
 

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Discussion Starter #4
ya i have been doing everything with the cover on. although yesterday i took everything off filter and cover,its just a stock filter,it didnt make a difference,took spark arrestor out it didnt make a difference but i could very clearly hear the backfiring, its all back together now. i checked the carb boots both sides. they were tight. i tried spraying a little carb cleaner on connections, i know it eats the crap out of plastic so i stopped,but i didnt hear a change in rpms. i will try the brake cleaner tomorrow because i dont think i sprayed enough so that it would make its way in. the weather actually has gotten warmer,gradually though. and not by much its snowing here right now and i just tried it and its still the same. i have the carb in my hands right now. i have a flashlight on it. and am checking EVERYTHING. i thought i thoroughly cleaned it 2 days ago but maybe not.

Thank you for the reply i will try the brake fluid tomorrow and post results.
 

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ya i have been doing everything with the cover on. although yesterday i took everything off filter and cover,its just a stock filter,it didnt make a difference,took spark arrestor out it didnt make a difference but i could very clearly hear the backfiring, its all back together now. i checked the carb boots both sides. they were tight. i tried spraying a little carb cleaner on connections, i know it eats the crap out of plastic so i stopped,but i didnt hear a change in rpms. i will try the brake cleaner tomorrow because i dont think i sprayed enough so that it would make its way in. the weather actually has gotten warmer,gradually though. and not by much its snowing here right now and i just tried it and its still the same. i have the carb in my hands right now. i have a flashlight on it. and am checking EVERYTHING. i thought i thoroughly cleaned it 2 days ago but maybe not.

Thank you for the reply i will try the brake fluid tomorrow and post results.

Brake fluid is real rough on plastics too, use starting fluid / ether instead, it evaporates real fast.

When you cleaned your carb did you take all the jets out, and visually look through them after cleaning? I usually use a strand of copper wire or piano wire to run through the holes just to make sure nothing is lodged in them.
 

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Discussion Starter #7
i just spent a couple hours cleaning the carb, i did use some copper wire to clean out the holes,they all look perfect, the only thing i was thinking with the carb would be the needle valve. i saw a picture in the manual where the 3 inch needle went through the white plastic spring seat, i dont remember it being like that. right now i have the needle goes in first up through to the main jet,then the white spring seat goes down onto it,not through it, then the spring goes over that. the picture confused me because the needle is sitting there through the spring seat. i tried running it with the air box off and it was the same thing. thank you for the replies guys. i know we will figure this out im just totally stumped right now. tomorrow i will try the starting fluid.
 

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i just spent a couple hours cleaning the carb, i did use some copper wire to clean out the holes,they all look perfect, the only thing i was thinking with the carb would be the needle valve. i saw a picture in the manual where the 3 inch needle went through the white plastic spring seat, i dont remember it being like that. right now i have the needle goes in first up through to the main jet,then the white spring seat goes down onto it,not through it, then the spring goes over that. the picture confused me because the needle is sitting there through the spring seat. i tried running it with the air box off and it was the same thing. thank you for the replies guys. i know we will figure this out im just totally stumped right now. tomorrow i will try the starting fluid.
The needle goes into the slide first. There may be a washer spacer on top of the needle but not always, then the white plastic needle retainer then the spring.

If you look at the exploded diagrams on many of the only line parts dealers like babbits or country cat you can see the correct order of assembly for your particular model.

Some backfiring during engine braking is normal as long as it is not loud explosive backfiring. This is usually caused from the PMS, Pilot and sometimes the needle being set to lean. To enrich a stock needle you can shim it higher with 1 or 2 #4 machine screw washers. You turn the PMS counter clockwise to enrich also. Chances are you pilot jet is a #40, Many install a #42.5 or #45 to enrich the bottom end. Local Harley Davidson shop often carries pilot jets.

When cleaning a carburetor it is also very important to clean all the tiny air and fuel passages in the carburetor body. I soak in carb cleaner then hit every hole and port with compressed air. There should be a couple tiny ports in the bottom 1/3 of the carburetor main air inlet to the venturi. These are Air bleed ports that supply air to the needle jet and pilot jet, if they are plugged fuel will not be correctly atomized as it exit the jets into your intake. These are often overlooked.
 

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little bangs and pops,its all broken up sounding "Loss of top end power" it doesn't want to die but it wont accelerate any faster.
One thing you didn't tell use, what rpm is this happening at.

Almost sounds like your against the rev limiter.
 

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Discussion Starter #10
thank you guys for the input, i really appreciate it, i am going to try starter fluid around boots today, ok so i have the needle valve correct thank you wyo-h1, tex it is happening around 3,000 rpm, and come to think of it i think with the throttle wide open,the rpm should go way way up very quickly. i dont think they were. when i go out i put it in high gear gradually go up to about 10-12 mph, open it up, and it constantly pops and backfires and wont pick up speed maybe about 20 mph. i was just on lake winnepesaukee ice fishing a week ago and was able to go like 25mph, i never snapped open the throttle just normal riding and it was fine. im gonna read up on the rev limiter today.

one of the big black square fuses, i think it died because you have to hold the brake in now and you can hear a contact click(1 quiet click) where the fuses are. so it wont start without the brake on, and the 12v contactor relay for the winch control recently went on me,it looked crappy inside. maybe somthing is going on with an electrical component. if anyone knows where the magneto or stator is on the 06 500, or what i should test ohms or volts on i will try that too, i will look today but i think its inside somthing. thanks ill be checking back throughout the day
 

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Discussion Starter #11
sprayed starter fluid on boots,no increase in rpm. not sure what its called but the airbox near the radiator. i imagine engine needs to get air from some place, but this box is not sealed in any way.this is probably normal, when i sprayed starter fluid in it the rpms got lower.
 

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Discussion Starter #12 (Edited)
just pulled plug to do compression test. i rode it more yesterday than the day before... it is "BLACK" today. i cleaned the carb yesterday but didnt drive much after.so i dont think me doing anything to the carb did it. the carb looks the same everytime i clean it. theres a few holes they all work and are clean. my question is. with no performance mods of ANY kind why would a stock carb need to be rejetted,if this is what needs to be done that is. what should i do to get the plug back to brown? and also, it wouldnt be from spraying a little starting fluid would it,it had no affect and only bogged down for a couple seconds when sprayed front air box. anybody have any ideas. thanks
 

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just pulled plug to do compression test. i rode it more yesterday than the day before... it is "BLACK" today. i cleaned the carb yesterday but didnt drive much after.so i dont think me doing anything to the carb did it. the carb looks the same everytime i clean it. theres a few holes they all work and are clean. my question is. with no performance mods of ANY kind why would a stock carb need to be rejetted,if this is what needs to be done that is. what should i do to get the plug back to brown? and also, it wouldnt be from spraying a little starting fluid would it,it had no affect and only bogged down for a couple seconds when sprayed front air box. anybody have any ideas. thanks

Drastic change in elevation or temp can cause a need for rejetting, has it gotten a lot warmer? If your plugs are black and oily that is an indication of being rich.

If your air filter is extremely dirty it will also cause a rich condition.
 

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Discussion Starter #14
it has gotten a little warmer but not much man. it wont go over 17MPH!!! full Wide Open. this is ridiculous. i just got fed up and took it on the street,massachusetts wouldnt let you slide if they saw you on it. they would flip the lights on and risk lives to get at ya probably lol.; But it definately was not this bad last week. i was going 25 on the tracks that the snowmobiles left on winnepesaukee last week no problem. and now wide open 15-17mph max.bogging,choking,popping,... everything is clean or new,hoses are all in good shape no cracks no clogs,good fuel,fresh oil,the ignition coil though im hung up on this, 2ndary coil should read 5-7000 ohms, mine is at 16.42k the k has to mean thousands right? I measured from inside plug boot to the spade connection. could this be the issue,could it be a bad fuel pump. its making me sick im not a mechanic or anything but usually can figure anything out with a computer handy,and some good advice, ill keep you guys posted thanks
 

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just a shot in the dark , let your cat idle a bit , then feel the voltage regulator box-wires to see if they get hot, if so it may be the volt. reg. box.
 

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This same problem happened to mine after I took it swimming. except i could only get about 10mph out of it. I drained gas out of the carb from the drain screw untill it ran normal. my theory was it vapor locked at either the tank or the carb. Check your gas tank vent. if that is plugged it has problems getting fuel to the carb. also check any breather on the carb. If your getting enough fuel to stay running, but slowly, your carb is still letting air in to what your throttle postion tells it to causing the lean condition. your probably getting enough gas to drive slow but any more than that causes not enough fuel and to much air. It still doesnt explain your black plug and im not a small engine mech. but it worked for me. Good Luck
 

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Seen issues like this before after a carburetor was cleaned. First of all are you sure it got reassembled correctly? The main jet and the start jet will interchange and easy to mix them up. The one with the largest hole and number goes directly under the needle.

Second, Is the cap over the diaphragm sealed and installed correctly. No tears in the diaphragm? /If you move the slide with a finger does it slide up and down smoothly against the spring pressure under the diaphragm cap?

Third, looking into the main bore of the carburetor there is a hole that the needle slides up and down in. Is there a little stainless steel piece sticking up into the bore a tad? that is the actual needle jet that the needle slides in and out of. Once before I've seen where that needle jet came out during cleaning and did not get re-installed at all. the needle jet is held into place by the long brass threaded piece with holes along the side that the main jet screw into.

Forth, could you of bent the little tab that contacts the float needle or forget to put the pivot pin in or maybe the float pivot pin or the needle fell out when putting the float bowl back on?

Your symptoms resemble incorrect reassembly somewhere in the carburetor following your cleaning attempt. Is there any friends around that have does this a few times, many times two heads are better than on when trouble shooting
 

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Discussion Starter #18
I am definately thinking the needle valve diaphram as well.or float bowl set up,i may look for a carb online, as much as i dont believe its the carb because everything looks fine, it could be somthing that i just cant see. the diaphram is a really flimsy thing and you probably cant take it apart a bunch of times before it needs to be replaced. i did notice that it isnt really sealed at the bottom, its not torn or anything, but if i very gently pulled on it it would come up maybe 1/16th", most likely seals when closed and screwed down, its not the top where the cover and gasket go on but the bottom against the green part inside carb. that stainless steel tube is in there, it fell out of somwhere when i had it out to clean, i looked at diagram and did put it back in the main jet, and it sticks out the length of the narrow end maybe 1/4"" into the carb. i thought for sure i may have had the jets switched too but put them in correctly and no change. the needle valve does move freely and feels smooth,it sucks air when i move it up and down. the float bowl though,if you take off float bowl and needle and everything so that its just the hole that the needle goes in, is there some kind of gasket in that where if you blew into it ,air would not go through. i read somthing where somone asked if they blew air into this part and break that gasket. it may have been somthing totally different. just wandering cause i can blow through mine no problem.also when i blow into it when float and needle valve is installed there isnt really a middle ground where air wont go in then gets easier and easier. Air either goes or wont go, no matter how slow you raise or lower it. i thought it would be a gradual thing the lower you go where its easy, easier, open, or just closed. the fuel/carb vents are clear i tried putting all vent hoses up down sideways. appreciate you guys helping out. ill try some more stuff today. any input greatly appreciated as im almost out of ideas
 

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Discussion Starter #19
Well I spent another 5 hours today on it. I read up on finding top dead center,if valves were suppose to be at 007-009 i put 008 feeler gauge in and tightened them up. didnt make a difference.triple checked carbs there fine..this all happened randomly the other day and then i cleaned the carbs after that. 1 thing i did notice is that the fuel pump isnt clicking as loud as it was. but it did shoot fuel out pretty strongly as i turned flywheel to find top dead center.another thing MOOGWAG, i let it idle for 20 minutes.it idles perfectly,and low rpms perfectly. i dont know exactly what the regulator is but i thought it had somthing to do with the box near the taillight i think the rectifier. the 3 yellow wires ,THAT CONNECTION WAS SIGNIFICANTLY WARMER THAN THE OTHER WIRES. WOULDNT CALL IT HOT but if the other connectors were air temp(40) this connection was maybe...65-70. any and all suggestions appreciated. thanks
 
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