2004 rubicon 500. (Trx500fa) It will cold start and run PERFECT. I mean no smoke, no tics, idles absolutely beautiful. Rev it up perfectly. But after a few minutes it will start to sputter out and die. Trying to give it fuel makes it worse. If it does recover it’s fine again. But usually it dies and won’t start back unless it sits a while. & backfires when trying to start it back. Let it sit, starts perfect again. Brand new oem Honda carb, plug is getting great spark. Even when it sputters out, I took the plug out and had bright blue spark. I put volt meter on battery and it’s charging good which makes me think stator and regulator/rectifier is good. I first thought it was maybe a overheat problem but everything checks out good there I think.. Because as long as you stay riding it does fine it won’t die at all. Rode it enough for fan to kick on once. Ride around as long as you want pretty much as long as you don’t stop. Just when you stop it’ll eventually start sputtering out and die. Backfire when trying to crank. I thought maybe valves needed adjusted but they sound good can’t hear them at all and I don’t think they would’ve tightened over time. Older ones cdi would get hot and quit but I’m still getting spark. I’m lost man. Good gas, good flow from petcock to carb, & tank vent is clear. I’m stumped. It runs too perfect at first to have jumped time or something like that. No smoke, tics, nothing. Runs and sounds great, pulls hard. Just can’t stop… any help is greatly appreciated. Thanks for any advice.
Tried all I know. Need help please! 2004 foreman 500
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don't know much about them atvs but sorta sounds like a fuel issue. Not sure if it has a fuel pump but thats sounds like it may be the issue. Could be a dirty jet in the carburetor. It sounds like its either getting too much fuel or to little. maybe bump the idle screw up a bit. hope this helps and hope you find your issue
Hey thanks for the response bud. I thought the same but I’ve triple checked fuel side. No fuel pump on these models, just gravity fed to carb. New carb and cleaned tank all that before hand. I don’t think it would have clogged a jet again I got it real clean. I tried a couple different mixture settings and just set it back to factory spec. I got ahold of an old friend that’s a dealer mechanic for Honda and he told me to check the valve clearance next so I’m gonna go from there. I will follow up and share my experience in hopes it will help someone else. Thanks again.
kinda sounds like the float in your carb, i had a float once that had a leak in one side, it would fill with gas and as long as you where rideing using fule it never caused a problem, but if you stop for any amount of time it would fill that one float and cause it to stick open allowing fuel to flood the cylinder and back fire sputter and die, wont start till the cylinder dries out, then starts up, revs up and if you dont take off...........rinse and repeat!
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Check the spark plug-is it sooty?
maybe the choke valve on the carb is stuck open so the enrichment circuit stays open. I would consider changing the choke valve; then the CDI. BTW get a rebuild gasket kit for the carb while you’re buying the valve. Get free shipping over a certain amount
use the oem parts finder at Rocky Mountain atv and Partzilla
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maybe the choke valve on the carb is stuck open so the enrichment circuit stays open. I would consider changing the choke valve; then the CDI. BTW get a rebuild gasket kit for the carb while you’re buying the valve. Get free shipping over a certain amount
use the oem parts finder at Rocky Mountain atv and Partzilla
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kinda what I was thinking as well.
Again, brand new oem Honda carb. No need for rebuild. Did same thing with other carb so float isn’t the issue. I did put the new choke assembly (piston, oring, spring) as well with no change. It’s not that. I’m fairly sure it’s not a fuel problem, nor electrical as I get great spark at all times. & the spark plug looks perfect golden brown no problem there. I wouldn’t think cdi either because even when it dies plug is getting excellent spark still. & everything is charging perfect and perfect spark. It about has to be tight valve clearances & when engine gets warm makes it even worse and won’t run. Mechanic buddy said they would actually tighten where the valve sinks into the head. If it’s not that, then I seriously have no idea. But I would say he’s leading me in the right direction. He’s a pretty sharp dude. All I can do is keep trying. Thanks all
If it also start's hard cold it could be the valves, the first sign of tight valves is hard starting in cold weather.
That’s the thing, starts perfect cold 🤯 then sputters out after running a few minutes. But it’s not a fuel issue because if I take off I can run it wide open pulls hard no issues. If it was running out of fuel it surely wouldn’t keep up with wide open demand. I’m so dang sure it’s not a fuel or spark problem because again you can take off riding just can’t stop and then won’t start back. & even after dying, still getting strong spark. All connections are good. Tight clearance on valves and when engine warms they expand further and choke the engine out. That’s all I can figure. Hopefully tomorrow evening I will find out.
I appreciate the advice bud. & no, I’ll have a $250 spare cdi laying around lol. I’m a diagnostic type person rather than firing the parts cannon lol. The carb needed replaced either way. Plus, I’m getting perfect spark & timing. So pretty confident cdi isn’t the problem. Even when it chokes out, still getting perfect spark. However, if adjusting valves don’t work that would be my next move although again I’m confident it’s not the problem. Worth adjusting valves for free first. Plus I have a good feeling that’s the problem. Tight clearances getting even tighter when engine warms up, & chokes it out. & that’s exactly how it sounds and acts.
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It could be your CDI when it gets hot it cant make the connections to work properly.
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CDI
Before you read all this, go to the bottom and read the last 3 sentences. I believe you have a fuel blockage problem. A wise mechanic told me that 90 percent of carb problems are electrical. So start by monitoring the spark until it dies. If it’s all good then move on to the backfire. If the spark weakens, the CDI unit Is suffering from heat which causes it to weaken and backfire. The back fire can also be caused by a lean fuel mixture. A lean mixture will make heat. I suggest checking the cylinder head temperature as soon as you stop and then see if it gets warmer before it dies. if the heat rises then you may have a fuel issue. Are you absolutely sure the fuel is good? The timing is fixed, so, let me guess, if it cools down it starts right up. Watch that spark until it dies.
When you open the throttle you are giving the engine more air which requires more gas. I would take the cab apart and check for obstruction. It sounds like it’s starving for fuel. GOOD LUCK!
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Capacitor discharge ignition
its the brain to you Quad its very possible and I think it is your problem. I had one do this . It would run cold but in a few minutes it would die and that was my Quads problem . Maybe you have a friend who has the same kind of bike , that you could borrow it . Or do this as soon as it dies ,check it for spark.
I appreciate the advice fellas. But if you will, go back and read my other replies. Spark is never, ever weak. Brand new carb and cleaned tank. There’s no fuel obstruction I’m 100%. & the older 300s had the cdi problem once warm I know, so I monitored that as well and I’m getting great blue spark at all times even when it dies. Again as I said in my other replies, I have been thru everything on the electrical & the fuel side. I’m ocd and I’m fairly sure nothing stayed in tank big enough to block a jet. Besides, it was doing exact same thing with original carb. So it’s not a fuel issue. & again all electrical has checked out so far. It’s charging, getting great spark, etc. all lights work and no electrical problems at all that I know of. I wish I had time to adjust valves and let y’all know for sure but haven’t had time after work yet. This weekend for sure. Thanks again y’all.
If the cdi messes up you dont get spark at the right time and they dont run right or at all but you still get spark when you pull the plug and check for spark.
Since it starts good cold, I highly doubt its tight valves as they get even tighter cold and cause issues when cold not hot.
Since it starts good cold, I highly doubt its tight valves as they get even tighter cold and cause issues when cold not hot.
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That’s why I asked about condition of spark plug. Lean will cause backfire and lightened coloring of plug. Rich will cause tough start when warm and darkened plug.
loss of compression caused by sticking valve or weakened valve spring is not something you can see.
if you can’t remember when valves were last set, good practice to gitrdun
loss of compression caused by sticking valve or weakened valve spring is not something you can see.
if you can’t remember when valves were last set, good practice to gitrdun
Sounds like something floating in the fuel tank that gets stuck in the outlet. Moving around keeps it free. Everything else sounds normal. Saw it once on a jeep. took months to figure out. Owner had a six yr old son that had lots of plastic cow boys and Indians. It was an Indian chief holding his rifle in the air. The density of the toy allowed it to half float. The rifle barrel was in the outlet. Rock the jeep back and forth and the Indian would slosh loose. Then everything back to normal till next time.
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