Can't get my FCR to idle

[NacsMXer]

Hi, ive had this problem for some time now and ive just learned to deal with it by applying a small amount of throttle to keep my quad idling. I have a FCR 39 and the idle screw is maxed out completely but the quad won't hold a steady idle on its own. The quad is jetted properly and has no problems with spitting or sputtering-it just wont idle by itself. I am wondering if changing the placement of the throttle cable on the holes on the pulley of the FCR would maybe help me out? It seems as if my throttle cable is adjusted properly to where it opens fully at WOT but it just gets a little annoying when the quad cant idle for more than a couple seconds without my thumb slightly on the throttle. Anyone got any ideas for me? Thanks for the help in advance.

[cals400ex]

is the idle adjustment working properly? or in other words, can you see the slides inside the carb really moving up when you increase the idle adjustment?

it is possible that you have an air leak. you need to first make sure the air boot connecting the carb to the head isn't cracked. if it isn't, make sure the o-ring is still in good shape where that boot does connect to the head. next, make sure the carb is mounted securely to boot air boots so the clamps are tight. it could be possible that you just need to clean the carb out. you may also need to take the accel pump off clean the heck out of that. what pilot jet you running? how many turns out on the fuel screw are you? what mods are done to your bike?

[NacsMXer]

Originally posted by cals400ex
is the idle adjustment working properly? or in other words, can you see the slides inside the carb really moving up when you increase the idle adjustment?

it is possible that you have an air leak. you need to first make sure the air boot connecting the carb to the head isn't cracked. if it isn't, make sure the o-ring is still in good shape where that boot does connect to the head. next, make sure the carb is mounted securely to boot air boots so the clamps are tight. it could be possible that you just need to clean the carb out. you may also need to take the accel pump off clean the heck out of that. what pilot jet you running? how many turns out on the fuel screw are you? what mods are done to your bike?

Thanks for the reply Cals, yes, the slide moves up and down slightly when I adjust the idle screw - Its just maxed out completely (on the fastest setting). I checked the air boot and all the connections are secure. The intake manifold boot was just replaced by Laz at GT Thunder because my old one was cracked. After he rebuilt my motor, I cleaned out the carb real well before I put it back on. Im running a 52 pilot jet with a 165 main with the fuel screw turned out about 2 1/2 turns. All my mods are as listed in my signature. I really think the jetting is spot on because the quad runs like a champ, it even idles fine but only when i have my thumb ever so slightly on the throttle. Its like the idle screw almost has enough adjustment to it, but its not quite making it-this is the point where my thumb opens the throttle just a tad more to the point where it will idle normal.
If it helps, I never had this problem before when my motor was just a 10:5:1 440 with the Web 450/451 grind cam. After I went to the stroker motor, port/polish, oversize valves, HRC cam, etc, etc. then I started having this idling problem.
Ill definitely spray some carb cleaner around all air boot connections to test if I do in fact have an air leak.
But if that's not the case, would adjusting my throttle cable help this situation any?
Thanks again.
-Chris

[Sc0]

I don't think this is it but is the slide and vacuum plate in right?

[speedy400]

yeah I bet your throttle calbe just giggled itself loose or what not, just try adjusting the cable and see what happends.-darren

[cals400ex]

i don't see how adjusting the throttle cable will help. when the bike is at idle, the cable should have some slack in it. whether it sticks or not, the idle shouldn't be low. if it was idleing high, i would say the cable might be sticking. maybe i dont see what your saying? :confused:


ok, i would make sure all the drain hoses off the carb have no debris in them and aren't clogged. i would try to take the carb off again. i would take the pilot jet, fuel screw, air screw, main air jet, etc out and spray the heck out of the carb and make sure none of these jets are clogged. i would also take the top of the carb off so you can spray the needle and needle assembly down too. all it takes is a little piece of dirt to cause a headache. i am not promising you it is the carb, but i would start there.

also, i would consider raising your pilot jet up to a 55 or 58. it seems like my buddies 10.8:1 416 likes a 55 pilot. you may need to tinker with that fuel screw too. it is a pain unless you have one of the adjustable fuel screws. if you don't have one, i would buy one. it makes the job much easier.

i assume you don't have any exhaust leaks either? yes, spray starter fluid on all carb and air boot connections to check for leaks.

with the mainjet, is that the size Laz told you to try? i figured that may be a tad small for your motor?


i assume where the idle adjustment tip hits the carb pulley everything looks good there? it isn't possible for the tip of the idle adjustment to be broke and thus it being short and not reaching far enough? the pulley isn't bent at all which makes the idle adjustment harder to reach, is it?

i am just trying to throw out suggestions. :(

[Doibugu2]

I took mine apart and then put it back together wrong. I forgot what I did, but I could tell the wheel where you put the throttle cable to wasn't going all the way back to the correct position.

Yours sounds like what mine was doing, it would run fine, just wouldn't idle.

[NacsMXer]

Thanks for the replies everyone.
Ill definitely try cleanin the carb out and blowing it out with compressed air. I too, thought that my jetting would be a bit low but when I asked Laz about this he said my 52-165 jetting was ok. I of course, know that jetting varies from region to region along with temperatures so he couldnt be that exact; maybe he was just giving me a good baseline to start from. I even confirmed this with C&D racing when I was installing my adjustable fuel screw and they said it was fine. The quad runs great and is a monster, but now im wondering if I can squeeze out some more power if i bump up the jetting a bit. Ill also tinker with the fuel screw a bit to see if that helps any. cals- I know youre an FCR expert so do you think you could give me a better jetting suggestion for my motor package besides the 52-165 i have now? Again, thanks so much for the help. :)
-Chris

[cals400ex]

well, it is hard for me to tell. i haven't spent as much time on the fcr's as i have with the stock carb. when i had my fcr39, i actually ran exactly 52/165. however, i only had a 10.8:1 406 with the stock head. some people say that after they get a full porting they actually need to go down on their jetting. i don't know because my head is still stock. do you have the air box lid on or off?

when it comes to jetting, i like to go as small as possible without running it lean. everyone has their own idea on what lean is though. after doing a full throttle plug chop, i like my plug to have a slight change in colors right on the bend of the tip of the spark plug. it may be hard to see but there will be a very slight color change. also, you may only be able to notice the color change on one side, the other side may not be too noticable. if the slight color change is above the bend, go down a size or 2 on the mainjet. if the color change is below the bend, go up a size or 2.

i do a lot of plug readings. some people don't like them these days. i have ran amoco 93 octane and also 100 octane aviation fuel. both will have different additives in them to make the plug a little different color. however, i can tell by looking at the plug there isn't all that much difference.

i probably would go up on the pilot jet 1 size. maybe you don't need it, i don't know. i think laz would be able to get you close. if it is running fine, you may not need to change. i would just check the plug and go from there. good luck

[NacsMXer]

Hey, thanks again Cals for a very thorough explanation. I appreciate the tips on the coloration of the spark plug bend - you learn something new everyday. I run with the airbox lid off. Ill try out goin up one on the pilot too just to see if it changes anything. Ill definitely try out your method on the plug chop too. By the way where is Staunton located? Im always happy to meet new people from this site. I usually ride at Motorsports Park in Byron, IL. Its right next to the nuclear powerplant.

[cals400ex]

by the way, the pilot jet shouldn't really affect "how the bike runs." the pilot jet is mainly used for 1/8 throttle and less. i just like to be a tad rich on the pilot jet so when i stop for a minute and let it idle i am not lean. lean is when it is running hot. the richer you go, the cooler it will run. when your moving, you have air to cool you down. at rest, you don't.


staunton is about, 15 miles southwest of litchfield and 20 miles north of edwardsville. i am not sure if that helps any.

[FatBoy Racing]

you might try a smaller spring where the idle adjuster screws into the carb body. I had to replace the idle adjust cable/screw on mine recently with something off another bike and had to do some mix/match with springs until I got the right combo. You may even elect to just snip a coil or two off of your existing spring. Kinda mickey I know, but it sounds like you just need a slight bump.

good luck

[NacsMXer]

Thanks again everyone for helpin me out. :)