Red Forman 1 Posted April 15, 2020 I have a 2003 TRX 450 FM, when I first start it runs rough and sounds like it's missing, I have to use the choke or give it some throttle just to keep it going or it will shut off. When it's warmed up it runs better but still sounds like it misses but will idle on its own. I'm not sure where to start, timing, alternator, or carburetor? 1 Share this post Link to post Share on other sites
sublime68charger 172 Posted April 15, 2020 (edited) how old is the gas that is in it? id start with a new spark plug. Air filter as well, due some of the basic stuff before you dive into the more advance stuff. and im not a great atv mechanic at all but hopefully one of the more advance members will be by and give you more to due shortly! how many miles on the ATV oh and welcome to atvhonda Edited April 15, 2020 by sublime68charger Share this post Link to post Share on other sites
shadetree 5,880 Posted April 15, 2020 start by purchasing a shindy carb rebuild kit, over haul the carb, give it a good cleaning before you go putting it back together. how old is the fuel ?, has it been sitting for awhile ?, give it a fresh tune up, new air filter, new spark plug, wouldn't hurt to change the oil and oil filter, DO NOT INSTALL THE OIL FILTER BACKWARDS !!!!. check the compression, check the timing, check/adjust valves if needed ?. most times, when they only run on choke ?, this tells me you go issues with fuel delivery ?, dirty carb ?, dirty fuel ?, low compression ?, timing is off because of a stretched cam chain ? ( this is why i say check the timing ! ). maybe an air leak around the intake boot at the intake ?. 1 Share this post Link to post Share on other sites
Red Forman 1 Posted April 15, 2020 Fuel is fresh, just changed the spark plug oil filter and air filter. I've never done a carb clean or rebuild on this machine yet. can I check the timing without removing the front crank case cover? Share this post Link to post Share on other sites
shadetree 5,880 Posted April 15, 2020 24 minutes ago, Red Forman said: Fuel is fresh, just changed the spark plug oil filter and air filter. I've never done a carb clean or rebuild on this machine yet. can I check the timing without removing the front crank case cover? you should down load the service manual, read it, then read it again !. no you do not need to remove any engine covers. you will how ever need to remove the sight cap inspection, right rear, allen head wrench, i think its 6mm ?, remove it, remove the pull starter from rear engine, so you can access the 17mm bolt on the crank, remove spark plug, with a 17mm socket on the crank bolt, turn it clockwise, with a flash light, look into the sight hole, watch for the T mark to show up on the flywheel, it should line up with the index in the hole, now peek at the back of motor where your 17mm bolt is, notice on the starter cage, on one of the tangs, there is a line stamped on it, it runs from front to back, straight line, it should be facing the raised arrow stamped on the case right behind the starter cage, roughly between 12-1 o'clock ?. if all these timing marks line up ? then your cam chain is ok. but with it being the year it is ?, i'd say it prob needs a new cam chain ?, i only use D.I.D. cam chains. Share this post Link to post Share on other sites
bcsman 1,381 Posted April 15, 2020 Think if take the 2 pieces of advise from @shadetree about ordering a Shindy carb kit and detailed instructions on checking the timing chain will have your 450FM running like a top...... Share this post Link to post Share on other sites
Goober 1,555 Posted April 16, 2020 5 hours ago, Red Forman said: I have a 2003 TRX 450 FM, when I first start it runs rough and sounds like it's missing, I have to use the choke or give it some throttle just to keep it going or it will shut off. When it's warmed up it runs better but still sounds like it misses but will idle on its own. I'm not sure where to start, timing, alternator, or carburetor? I didn’t see where you described your history with this quad, but this says dirty carb to me Share this post Link to post Share on other sites
01RUBY500 1,253 Posted April 16, 2020 8 hours ago, Goober said: I didn’t see where you described your history with this quad, but this says dirty carb to me Agree with it being a dirty carb, or at least starting there at this point. And a easy cheap carb clean would be running a tank of gas through it with a heavy concentration of carb cleaner mixed in with the gas ⛽️ and see how that helps. Share this post Link to post Share on other sites
toodeep 1,758 Posted April 16, 2020 Now days one of my first questions are is it still the OEM carb or a cheap replacement? The cheap carbs are a hit and a miss for a good one and most are jetted incorrectly. Share this post Link to post Share on other sites
Goober 1,555 Posted April 17, 2020 If you have a chunk of rubber or dirt stuck in a jet, carb cleaner won’t flush it. I been there a couple times. Share this post Link to post Share on other sites
