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Posted by: LT80
Did it run correctly when stock?
Why do you feel it needs a bigger jet?
Posted by: Mars
Hey Trailblazer.
You got some great info so far but I have some good and bad news.
The good: You may need a larger fuel line or fuel tank petcock. Not to hard to figure out. Get some clear hose/tubing from the local hardware/marine store. Get some OEM size and some next size up. Run the unit on a lift/ jack wide open and "see" what happens.
The bad: drilling the jets may get you to the right size for WOT but most jets are tapered bore. This helps the needle seal the " idle/ low speed" fuel control vs "on the main" fuel control. If you get wide open right it still may run poor or load up at less than WOT.
Best of luck.
Posted by: Mars
Quote
Originally posted by: Bendman
Mars, Who's Trailblazer ???
SORRY. Eyes getting crossed, staying up too late.
Posted by: Mars
Quote
Originally posted by: 222
BIG SNIP>
Mars, just to be clear, we are drilling the float needle seat, not the main jet. But if we were drilling the main jet, I'm not sure I understand the problem your talking about on the main jet taper - I may have misread your post, though. The needle slides down inside the main jet at idle, but fuel flow is metered at the top of the needle where it meets the carb bore, not at the main jet; once you begin to open the throttle, it leaves the main jet completely and fuel is regulated by the varying taper of the needle at the carb bore.
222
Yes I did misread the post. I did not read "needle seat". On the needle thing......I may be a bit behind on the newer carbs. I remeber needles droping all the way into the main jet bore. I have accually replaced worn/oval jets in some old bikes.
I'll go back to my corner now.....
Posted by: 222
srpreditor is leading you in the right direction. You are not even close to big enough jetting once you remove the airbox. We had to drill jets also at first, but then I found some big jets (very hard to find anywhere).
The next problem you might see is that once we went above about a 100 main jet, the thing would run fine and then start misbehaving. Finally figured out that the needle seat would not pass enough fuel to supply the main jet, thus running bad once the float bowl got low. The main jet hole was bigger than the needle seat hole!
Happy tuning
222
Posted by: 222
yes, we had to run the needle clip all the way up (clip down) to run very good. We ended up going to a different needle, because we still weren't satisfied with performance.
Just to be clear though, when I spoke of the needle valve, I was talking about the float needle valve (the one that shuts fuel off or lets it in depending on float height).
222
Posted by: 222
Bendman, your atv IS running out of fuel when it dies after the throttle being pinned for a little while. The float needle valve seat has so small an opening that it can't keep up with the fuel requirements, so the float bowl eventually goes dry. You (or preferrably your dealer under warranty) can take a drill bit that is slightly bigger and open the hole. The float needle should still have enough taper left on the viton tip to seal the bigger hole.
If you do some measuring, you'll find that the hole in the float needle valve seat is barely bigger than the main jet hole. I don't know why the mfg is using such a seat?
222
Posted by: 222
It is good to have people say "thank you"! I appreciate it guys. I spent countless hours and money trying to solve these problems, so there is no need for you guys to have to reinvent the wheel.
Anytime you have questions, post them; and if I don't check the forum for a while, just email me at recreationspec@aol.com - I check email almost daily.
good luck and thanks for the invitation to look you up! We travel some to race, so maybe I'll meet you in the future.
222
Posted by: 222
This is a mfg defect and should be covered, no questions asked! Truth is, they probably have several units out there with the same problem. You shouldn't have to figure out which jet is which, they Should!
The one that says 77.5 is your main jet. It is OK as long as you haven't modded the air filter system. Your "float" is attached to your carb body by a pin - push it out and the float will come off with the "float needle" attached. The hole that the "float needle" comes out of is the "float needle seat". The small hole down deep in the "float needle seat" is the one that is too small - this is how fuel gets into the carb. You must drill it out - don't go too big or the little tip on your "float needle" won't be big enough to seal off the fuel flow anymore and gas will overflow all the time.
If your dealer refuses to honor the warranty and you aren't comfortable doing this, send it to me and I'll do it for you.
best wishes
222
Posted by: 222
Bendman, I may have mistakenly assumed the dealer checked for proper fuel flow to the carb when you took it in the last time. You said they found trash in the system. Just as a check, take the fuel line off the carb and turn the fuel on. It should have a steady flow of fuel. That line is much much bigger than the hole in the needle seat, so it should flow enough if no blockage in the tank, petcock, or fuel line.
You have drilled out to .080" on the needle seat, which should be more than enough. To check it on a stand, you'll have to hold the throttle wide open for awhile to give it time to run the float bowl dry. You can check it this way if the rev limiter is still in place. I know its frustrating, but a lean mixture can cause similar misbehavior. The stock jet may have to go up one size if the weather is real cold and dry where you are or if the air box system has been modified any at all.
Mars, just to be clear, we are drilling the float needle seat, not the main jet. But if we were drilling the main jet, I'm not sure I understand the problem your talking about on the main jet taper - I may have misread your post, though. The needle slides down inside the main jet at idle, but fuel flow is metered at the top of the needle where it meets the carb bore, not at the main jet; once you begin to open the throttle, it leaves the main jet completely and fuel is regulated by the varying taper of the needle at the carb bore.
222
Posted by: 222
Don't go there, we need experience and wisdom!
Posted by: Fastestdad
I bought a K/N air filter I wanted to use to replace the airbox on an arcticcat90 (taiwanese)similar to DRR,Kasea. It has the airbox under the seat with metal tube down to carb via rubber elbow. But I never could get it to run right any suggestions?? It had a 77.5 main jet stock I tried an 80,82.5,85,87.5,and a 90 main jet. It seemed to run ok at first with the larger jets but then would start to bog at low rpm within maybe 5 seconds and unburned fuel was building up on the filter side (not engine side) and I'm assuming bogging down engine. Anyone know a fix?????
Posted by: Fastestdad
Hey srpreditor what drill bit number or size did you use to get a 149 mainjet?? It'll let me know about where to start.
Posted by: Fastestdad
Hey bendman I wanted to answer your question. Yes the ac 90 ran good after I took out the restrictor out of the carb that only let the slide go half way open. Before that I was ready to get rid of it as I took mine to the dealer too. I also removed the inner/smaller little pipe from inside the muffler endcap by grinding it out(after taking off endcap). This still leaves you with the larger 3/4 inch pipe and looks stock. Then I rejetted up 2 sizes to a 82.5 and that really picked up the power. Like maybe 50% more power and costs $3. I was just getting greedy wanting more power by trying to use the K/N.
Posted by: Bendman
I just bought my son a brand new ac 90 a couple of months ago. I hate to say it but I have had nothing but problems. My first problem was the stupid dealer that I purchased it from put mixed gas in the tank. I had to take it into the shop to have it figured out. Then the next problem we have been having is similar to what maybe one of you are having. When he is riding and he has it pinned for any amount of time it seems to run out of fuel. It just starts bogging and if you keep pressing on the throttle it dies. I took it to another dealers service shop and they took it apart and said that it had junk in the carb. Don&39;t know how it got there. So I thought it was fixed. WRONG! The first time my son had it out the same thing happened. What do you guys think it is. I'm tired of forking out money for a brand new machine. That's why I buy new things, so I don't have to fix them.
Posted by: Bendman
222, thanks much for the info!!
Posted by: Bendman
222 I talked to my dealer and they said that it would not be covered under my warrenty. I took the float bowl off of the carburetor and there is two little Brass screws (needle seat's) ??? one is larger and sticks out the other small and is up inside one of the housings that sticks out from the body of the carb. The larger one says 77.5 on it. I don't know what to do from here. I don't know which one you want me to drill. Thank you for your help 222.
Posted by: Bendman
222, Thank you very much for the reply. I did what you said. I ended up opening up the seat hole to 5/64's. That's as wide as i could go and still have the flaot needle work. I just took it out in my driveway and it's still doing the same thing. It could be a little better but I can't tell. what do you think?? maybe a bad filter? Do I need to order a bigger needle and seat? Maybe?
Posted by: Bendman
Mars, Who's Trailblazer ???
Posted by: Bendman
222 Thanks for your help. I checked the fuel line to make sure it was getting fuel. It has a steady stream of gas coming out it&39;s not much but its steady. I checked the plug and for my taste it&39;s a little light. I don&39;t know though. The color is kind of like a light gray with a purple hue. Too lean maybe like you were saying?? Thanks to you I know where the main jet is know I could change it.
Posted by: srpreditor
my son has a 90 preditor i have put the fmf pipe and the k&n filter on it and i am at a 149main jet just to get the thing to fun, we had to drill the jet to make a 149 seems to run good
Posted by: srpreditor
thanks trailblazer, one other thing on the neddle valve i had to lower the clip to the bottom try that with a 149 jet, with a k&n filter that should work for u.
Posted by: srpreditor
i think u need to remove any jumpers from the cdi, there is a metal clip between two screws, remove the clip. change the plug, remove the oil tank and premix the gas yourself so u know what the mixture is i would say 32 to 1, thats what i fun in my 90 preditor have had no problem with fauled plugs, use premium gas, and always buy it at the same place it makes a differance, if this dont work let me know.
Posted by: srpreditor
fastdad that is a size 53 hope it helps
Posted by: srpreditor
222 that is what ive been lookig for with the 149 main jet the thing was running out of fuel climbing long hills. will drill the float fuel opening to at liest the same as the main jet, if the dont work i will throw away the carb and start over. thanks again if u get over to the caost give me a buzz.
