Polaris Riders Forum banner

1 - 20 of 20 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter #1
i have just got done completly rebuild a 2004 predator 500 engine. New crank, piston, main bearings clutch valves. etc.... it ran great for the first hours and now its cutting out (like its loading up) at 1/2-3/4 throttle. I've jetted and jetted and then jetted some more and changed needle and clip pos. i've adjusted the air fule screw, float bowl and everything. so i finally broke down and tried that dyno jet kit. still same problem. i have complete cleaned and service the entire carb and fuel system. i have seen on here that some other people have had this same problem. has anyone found out what causes this know problem?? and i am a certified motorcycle mechanic myself so please dont reply with " have you check if you have a full tank of gas.." thanks!! ohh and i live the mojave desert at alt. 2000-2500 at about 70 deg right now. thanks!!
 

·
Premium Member
Joined
·
575 Posts
Well, if it is just 1/2 - 3/4 throttle it sounds like a needle problem..no need to mess with the fuel screw as it is just idle, no need to mess with main jet as it is just 3/4 and above..sounds like a needle adjustment to me...or maybe a choke issue...remove that puppy and clean it real good....also try pulling the choke out as you are riding and see if that helps or hurts, then you know whether you need more or less fuel....what kind of air box are you running?
 

·
Registered
Joined
·
6 Posts
Discussion Starter #3
like i said before i changed needles and every thing with the carb and cleaned it completely. its 100% not the carb. i have a stock airbox with a uni filter in it. and a stock exhaust. has anyone experienced this problem??
 

·
Premium Member
Joined
·
8,086 Posts
I think it could be too lean on the main. If the main is too lean then it wont get to full throttle without popping. what main are you running?
 

·
Premium Member
Joined
·
4,620 Posts
i also think it has to be a jetting issue unless your timing is off. if you could atleast indulge us and tell us exactly what your jetting is, main jet, needle position, pilot jet, and fuel air screw. then we can help you from there. if we can eliminate jetting in our minds maybe something else will come up.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #6
okay..i have now a dyno jet kit with there needle at the 2nd. fule screw 2 turns out and the dyno jet 165 main with a stock 45 pilot. i have tried to lower clip one at a time and no better i tried raising one at a time no better. i tried the same system with the stock needle no better. i tried the dyno jet main 165-175. and a brand new spark plug DCPR8E (stock) at the correct gap. the only thing i found on the forums is that someone else had this problem and they said the the motor jumped a tooth on the cams, so when i get home i am going to check that and see. thanks a head of time for everyone helping.
 

·
Premium Member
Joined
·
575 Posts
Could have a bad CDI too, but really guys..Fuel screw = idle and just off idle...needle = mid rpm's...and main jet = top end...If you are running perfectly on top end then you have a needle issue..or possibly CDI..maybe even the boot that your needle fits in could have a tare or hole in it ( under the top cap of carb). I find it odd that it ran good for awhile then started to act-up. I know you said it is not the carb, but make sure you cleaned all parts of the carb..removed all jets and blew out with air. Naturally I guess your carb is mounted tightly to your intake, no intake bolts have backed out and your carb boot to intake is tight...just thinking out loud!

Okay, just read your latest post...make sure you put your cam chain tensioner in correctly..pull it in, bolt it on, then release it to tension the chain...I am sure you did it right but just thinking out loud. If you skipped a tooth then you either have a stretched chain or a bad tensioner..check the inside of your valve cover to see where the chain may be spanking it at the corners..front & back above the cam sprockets....that is about all I can think of right now..your fuel screw could be out 1/2 - 3/4 more though I think
 

·
Premium Member
Joined
·
4,620 Posts
those are alot of good things to check. last thing i recomend is when you check your timing and check your tentioner after you release the screwdriver make sure the thing has good tension. if there is any play in the timing chain at all that is not a good thing it should be taught. i don't mean try and go gorilla tight and break your tensioner just give it a little hlep with the screwdriver gently to make sure you have full tension . then if it backs off and slacks up on it's own you either have a stretched chain, a bad/worn tensioner, or most likely both. if you have skipped a tooth on timing do not just adjust it back and run it. replace the timing chain, tensioner and check and double check the timing. make sure you turn the engine over by hand a few times and then check it again. if you go one tooth off oneway you lose power if you go one tooth off the other way KABOOM vallves into the piston they break and cram intot the head. so be careful.

definately check everything else too though. make sure the black boot in the carb is intact, make sure the needle is seating good and all that stuff jives. checking the intake boot for cracks tears or warpage is a great thing to check. bajapred cover most of my ideas. i just don't want you to miss anything. i hope it goes well. leo
 

·
Registered
Joined
·
768 Posts
check your battery connections. I had the same problem last year it was running great and started to cut in and out at 1/2 throttle. I messed with jets and cleaned the carb. By accident I bumped the positive lead on the battery and noticed it moved. Problem was solved. I quess it was getting enough juice to start but not when the rpms went up.
 

·
Premium Member
Joined
·
5,615 Posts
if you have a stock pipe and filter 165 is way rich for a dyno jet main. in so cal about 1200 ft. with a big gun and drop in k&n with 5 uni 1" vents in the air box I ran either a 150 or 155 main and needle 2nd with the thin washer 2.5. likely your needle could be rich for your set up but so is the main. remeber the thinner dyno jet needle is richer than the stock needle on each position.
did you read the plug. I bet it's black.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #11
i got it!! i havefound the problem the snorkal tube thing that is mounted on the bottom of the airbox fell out. i re-installed it and it runs bitchen!! thanks guys for the info though!!
 

·
Registered
Joined
·
6 Posts
Discussion Starter #12
and my final jetting is dyno jet needle at the 2nd from top with a 165 main which would be like a 153.5 mikuni jet. and fuel screw 2 turns out. and plug color is good.
 

·
Premium Member
Joined
·
5,615 Posts
the chart dyno jet vs mikuni is wrong. but if you got it running right thats good.my expeirience was that with the big gun and airbox mod I went down 1 size from stock jetting with the dynojet for that reason I feel the chart is wrong and just confuses the process. if you had a slip exhaust, airbox mod and jetting you would be able to wheelie in 3rd no problem or at least with the 04 trans gearing.
 

·
Premium Member
Joined
·
4,620 Posts
i agree with you 100% jm on the chart. i have tested tons of mikuni jets directly against dynojets on a drag strip with 2 predators and tons of runs, without any other changes. although i always found the dynojets with the dynojet needle to outperform the mikuni jets. measuring the inside of all the jets from 140 to 180 mikuni and dynojet they all measure the same example a 170 mikuni measures exactyl inside to a dynojet 170. the dyno jets do have a different taper to them but the center or narrowest part is the same. the only real difference in measuring the needles in everyway is that the dynojet needles have a more aggressive or narrower 1/4 to 3/4 of the needle wich will effect mostly the 1/2 throttle position. my brother and i did many roll on drags times also and found consistantly that at half throttle the predator with the dynojets did pull a faster time. also from a stop it had the fastest time every single test. not by much but dynojets always came out on top.

so although i think there is a difference the chart is way off in the way it compares the jets. they do not flow that much different at all. they measure the same. the needle is only slightly different at full throttle when the needle is almost completely out of the main jet there is no way that it flows that much different when the inside of the jets measure exactly the same. just my 2 cents.
 

·
Premium Member
Joined
·
5,615 Posts
exactly,your the only one that agree's on this. I have been saying that for almost 4yrs. LOL
oh well,you can lead a horse to water but you can't make him drink.
 

·
Premium Member
Joined
·
575 Posts
Well, here is how they mark their jets... Dynojets are marked in diameter of the hole..ie, DJ165 = 1.65mm hole....the Mikuni jets are marked by flow rate cc per minute..ie, M165 = 165cc of fuel per minute...as far as the holes they may be very similar in size from a DJ165 to a Mikuni 165, I don't know..also like LEO said they have different tapers between the 2 jets. I personally use the Mikuni jets, I have never had an issue with them.
 

·
Registered
Joined
·
6 Posts
Discussion Starter #17
LEO, I have just measured and compared Dyno jets to Mikuni jets. the stock Mikuni main jet 150 meaures exactly .0623" and Dyno jet 150 measures exaclty .0588". going drag racing is not a accurate way of saying that the jets are diferent. The tapers my be different but the ID (which is the orfice that acually controls flow ) is different. A Mikuni 150 is the same size as a Dyno jet 155 not a 150. The idea that the dyno jets are number as to MM (150 size jet =1.5 MM) is roughly true. a dyno jet 150 is .0590" which is 1.50MM. I have have complete set of Dyno Jets and every single on I measured and they are not the same to Mikuni's. It would be safe to say that Dyno jets are 1 size smaller than the Mikuni's. The chart that everyone is talking about is right but not exaclty is does show that the mikuni jets are bigger but they list it as way to big. and to add.....I did notice more power with the Dyno jet needle. the ONLY reason why i bought and choice to F*** with the dyno jets are because i had no choice. no one locally had mikuni jets and but they sold the dnyojet kit. I have always stuck with mikuni jets with a mikuni carb and a keihin jet with a keihin carb. everythough i did notice more power with the dyno jet needle for future tuning i will still use genuine jets.
 

·
Premium Member
Joined
·
8,086 Posts
My old outlaw needed a bigger jet, I had a 180 dyno jet and it needed one step bigger but not in kit.

Just for shits and grins.... www.chaparralmotorsports.com started putting pictues of their of the jets so you know exactyl what ytour getting. The are around $3 per. I thought its a good deal and an easy way to get jets being my dealer was a pain. I asked about jets and they said I had to buy 3 or more. BS. I usually wait till I need something alse and then get them. I got all the in betweens thatmy JD kit di not come with.
 

·
Registered
Joined
·
5 Posts
hey if anyone is still watching the post, i'm having this same problem i have also done everything with the jet that this guy did. i know my timing is good. but i''m starting to wonder if my airbox is causing this. it is a all aluminium box take two round k&n air filters but its bassically wide open the are no vent tubes to it so its not at all like the stock box. and just so you know i'm running a full big gun evo r exhaust, weisco 12.5:1 hi comp piston, a dynojet jet kit (set now at the second notch down on the needle, and a 175 jet, stock 45 pilot, and three turns on the mix screw, i am also running at sea level). and here is that air box i have:

Polaris Predator 500 Aluminum Airbox Air Box Intake CFM Performance | eBay


any help would be great on this as it is driving me crazy
!!





Update: i finally found my problem too. it is related to my air box but its not that its getting to much aid its that it not getting enough! the cover that is on my airbox when i remove it it works mint
 

·
Registered
Joined
·
1 Posts
i have just got done completly rebuild a 2004 predator 500 engine. New crank, piston, main bearings clutch valves. etc.... it ran great for the first hours and now its cutting out (like its loading up) at 1/2-3/4 throttle. I've jetted and jetted and then jetted some more and changed needle and clip pos. i've adjusted the air fule screw, float bowl and everything. so i finally broke down and tried that dyno jet kit. still same problem. i have complete cleaned and service the entire carb and fuel system. i have seen on here that some other people have had this same problem. has anyone found out what causes this know problem?? and i am a certified motorcycle mechanic myself so please dont reply with " have you check if you have a full tank of gas.." thanks!! ohh and i live the mojave desert at alt. 2000-2500 at about 70 deg right now. thanks!!
i had this problem, and it drove me crazy, it would come and go then only got worse. I read the forums and all that, tried everything, took carb out twice, cleaned it, took stuff apart all that crap, battled this problem on and off for few years, didnt drive mine much each year, so kept dealing with this each year, it was really pissing me off. so new filters, carb clean, injector cleaner, all kinds of stuff i tried to no avail, then i got to reading about filters and filter box again and thought i wonder if that little spongy filter material up under the gas tank that wraps around the Snorkel to the filter box lid has anything to do with it? BINGO !! I took it out, and since it was old and apparently didnt let hardly no air through any more, it WAS the problem ! Soon as i took it off and took atv for a test spin, my 600 ran like a scolded dog ! Like **** maybe i ought to enter a nascar race or something, ran better than it ever has.
So everything i had tried was in vein, it was just a little chicken **** spongy filter under the gas tank that wraps around the snorkel causing this problem. I have never wrote on a forum before, but felt i needed to share this on here cause i know how much this drove me nuts for a long time, And sure many others are having same issue, it was that simple.
 
1 - 20 of 20 Posts
Top