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engine starts and runs, then dies and won't restart

67K views 25 replies 10 participants last post by  Bennie 
#1 ·
Hi all, I'm new to this forum, and new to 4 wheelers. I recently bought a 04 Foreman 450. It would start real easy, but smoked like crazy. So I put a new piston and rings in, had the cylinder bored etc... Anyway, ever since I got it all back together, I can start it when it's cold ath the beginning of the day, and it will run fine for a few minutes, with no smoke or odd noises, then it will die, and I am not able to restart it untill the next day, after it sitting over night. I'm out of ideas

I've double checked that the fuel is on, and it flows well to the carb. the carb has been gone through and thoroughly cleaned, it's got a new spark plug, I've double checked the valves, and they are both at .006" I've tried a different coil, a different carb, different CDI (used)

I have no idea what else to do/check and hope you guys can point me in the right direction. Thanks for your help
 
#2 ·
welcome to the forum
1st thing i would do is check the compression both hot and cold (see if it differs)
2ndi would makesure there is no restrision in the muffler
3rd id change the sparkplug (if cracked it can stop working when it gets hot it expans)
 
#3 ·
Compression is at 148 cold, I will try to check it hot tommorrow.
I will check the muffler, however, it originally had a straight pipe on it (there when I bought it) and it did the same thing with it on there. It's got a used factory muffler on it now.
I have tried two different spark plugs, one came with the bike, the other brand new, no noticalbe cracks or deffects in either one, it has not run enought to color/discolor the new plug yet. Spark plug gap is set to .035 Also I've noticed that the plug is dry when I pull it out after it dies, I expected it to be wet, from attempting to start it, I thought it might have gotten flooded after cranking it for a little bit, but it was totally dry.
 
#17 ·
The boot checked out fine, no cracks, and spraying it did not effect the idle at all.


It runs great when it's cold each morning, but warms up and nothing. I don't know how the whole ignition system works, but is there some sort of sensor for the crank or cam position? or an engine temp sensor? If so could one of those be bad, and cause it that when it warms up that the electronic timing is off a little bit? What's the best way to check the physical timing? I don't think it's off though, as it runs great, and has tons of power, when it's actually running.

It's not vapor locking, as soon as it dies, I can open the bowl drain, and fuel comes out, and the carb doesn't get very hot, certainly not hot enough to vapor lock internally in the carb, and the fuel line doesn't get warm at all.
Thanks for all your replies and suggestions thus far....
 
#15 ·
Could it be vapour locking?? Next time it dies open the fuel tank and listen for air rushing in the tank.
 
#19 ·
After it dies and won't start back, have you checked to see if it's firing at the spark plug? That will tell you if it's an ignition problem.

I don't know how the whole ignition system works, but is there some sort of sensor for the crank or cam position? or an engine temp sensor?
There's a pulse generator (pickup coil) that measures the angle of the crank. That's what tells the ignition system when to fire. It's possible that it or the ignition coil could be getting hot and breaking down.

Have you checked the valve clearance since you put it back together? Maybe the valves are too tight and when the engine heats up, they expand and hold the valves open slightly. That might not be the problem, but I would check them anyway to eliminate the problem, if you haven't already.

All that being said, the fact that you said that the spark plug isn't wet after tying to start it, makes me think it's a fuel problem. The next time it quits, check for a spark at the spark plug and they should help you determine if it's an ignition problem or a fuel problem.
 
#21 ·
I've rechecked the valve clearance, and they are both at .006
There is spark even after it dies and is hot.

What i'm wondering is, being an electronic ignition, does the timing curve/advance change with the engine temperature, like it would on a modern pick up truck? If so, there should be a temp sensor involved, which if bad, could cause the timing to be off after it heats up. Does that make any sense? And is it a possibilty on this thing? If so, that would explain why it dies, and why the plug is dry, because the plug would still be firing, and burning off the fuel but just at the wrong time in the combustion cycle, for the engine to run. Maybe I'm way off, I'm just out of ideas at this point.

Thanks all....
 
#23 ·
No, I don't think it works that way. There is no temp sensor other than the oil temp sensor that is used to turn the fan on. I believe the ignition advance is pre-programmed into the CDI/ECU. In order for the ECU to use input from a temp sensor and adjust the timing, it would have to be a closed loop system and Honda ATVs don't have closed looped computer systems like automobiles do.

When you checked the spark, was it a good strong bright blue spark? If so, I believe you have a fuel problem. After it quits, have you tried spraying gas or starting fluid in the rear of the carb? If so, did it at least "hit" a couple times like it was trying to run? If so, you likely have a fuel problem.
 
#24 ·
If advance is controlled by the ECM it might tweak the timing based on temperature but I don't reckon it would swing it far enough to stop the bike if a temp sensor was off.

When you say it'll idle cold is that with the choke on or off?
 
#25 ·
clean ur carb
 
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