Okay, this thing is stumping me, my father, and even a veteran ATV mechanic. Here's what I know. Fresh rebuild with jug, piston, rings, gaskets, valve stem seals, etc. New fuel pump that is pumping plenty of fuel. Injector is spraying fuel into the throttle body. The gas is fresh. There is plenty of spark. Plug is not wet. Its a nice goldish-brown. The oil is fresh. The air filter is not plugged up. The engine is in time. It is NOT throwing any codes when I put it in dealer mode.

After the rebuild it ran like a beast! Rode it about two times for maybe 30 minutes. My father ran it a couple times to go check on hay and he said he noticed it started to stall when he'd let it back to idle or when he'd try to take off. I went to get it back out the next time to try seeing what was going on with it and now it won't start at all. The battery has been good and still is as far as I know. I know those older KQ are picky about voltage. I tried starting with the battery charger on it and it wouldn't start. It would occasionally fire but was more like an after thought, like something was turning it off as soon as it would fire. I do not know if the ecu in it is original or not but I've heard of the old ecu's causing problems. I'm not sure what it is... does anyone out there have any ideas or suggestions? This KQ has been nothing but trouble since I got it and I want to be able to enjoy it for once considering all the money I have sunk in it already...

 

Usual cause of problems with no fault code is a blocked injector, yes it fires some fuel in, but not enough. There is a tiny filter in the injector's inlet, which can be carefully cleaned out with a tiny screwdriver, then blown out with compressed air, you can see the difference as before, you usually can't see the mesh of the filter. Check the fuel pressure if that doesn't cure it, as you may have bought a faulty pump.

You mention lots of problems, we only sold a couple of 700s but had more trouble with them than all the 450s and 500s put together, except for frame breakages, which they all suffer from.

 

I cleaned the injector and still it did nothing but crank and cough. Pressure test came back at 43 psi like it's supposed to be. Cleaned tank out and drained gas. filter is still clean and new. Gas seemed kinda stale even though it is not that old but I did not notice any water. The fuel line is clean as well. Anyone have any other thoughts?

 

Merryman, Would you think the ecu is the problem at this point? How can you test it?

 

Never had any problems with a 450 to 750 ECU. If you are getting a spark and the injector is firing fuel in, I doubt if you have an ECU problem. What is the C-- mark showing on the fault code display?

Because it is so soon after a rebuild, it is possible you got something wrong, so check compression in case of a blown gasket or valve "crossover" due to incorrect timing. I had a 400KQ that seized the cam, due to a small blob of gasket sealent that had come adrift and blocked an oilway, a couple of years after I had worked on the engine.

 

Merryman, It reads -C00. The rebuild was actually done back in the winter but I didn't know till I took it to a friend who used to work on quads a month ago that I screwed up and put the top ring on upside-down which was why the engine was still smoking after the rebuild. He put the new rings on for me and a new head gasket and base gasket. I ran it a hand full of times and ran the best it ever has since I've owned it. Then the next couple times it would stall when idling then it wouldn't run at all. I've taken the valve cover off to check timing and everything line up. I turned the engine over to listen for any noises and watch the cams and they worked like they were supposed to. Today I took the magneto cover off to make sure the wood-drift key hadn't sheered per someone else's suggestion and it is all working properly so I can also rule that out.

 

Alright, here's the update. I'm an idiot. The reason it wouldn't start was b/c the spark plug end got bent up into the "electrode".... I think I dropped it after I checked spark but I'm not sure. Only other explanation is the piston smacked it.... It ran fine after the new spark plug. Dad went to move it an hour or two later and he said it kept stalling out when it'd go to idle like it was doing before. So now I don't know... I haven't had a chance to ride it for a period of time just yet but this thing is making me crazy and angry.. I just want to ride man... Is that too much to ask?!?! Anyone have any ideas?

 

Both throttle position sensors and faulty temp sensors can cause the cutting out at idle. On the temp sensor, (450KQ) turned out to be the wires to it, they are too short and with engine vibration they break, but this throws a code up. On the TPS, I did try moving it about and got it to run better, but nowhere near where the -C00 mark said it should be. It also wandered, running OK for a while then needing a different setting, so we fitted a new TPS and it was OK afterwards.

Just a thought, have you checked voltage when running, overcharging throws the ECU out, though again, it should fault code. Unmodified, the regulator should put out about 13.25v, no more than 15v

 

@merryman

Where is the location of this filter? I am having the same issues. Thanks for any help.

 

Sorry not to get back sooner, I've not been posting lately due to work pressure. As I wrote above, in the injectors inlet. I have given up poking with a screwdriver, I just blow down the injector's inlet with compressed air, from a distance, so the dirt can get out. You will then see the tiny mesh filter inside the injector. Have a 400KQ that needs the injector cleaning about once a month, although after a blow out it works fine for a while, a new pump, several filters and a tank clean out haven't cured it. So we are going for a new injector next time it does it.