Mech

Tapping around the edges of the cam cover might help get it free, but I'd just find somewhere to lever it up. Sometimes there's a small overhang somewhere on the outside where you can get a screwdriver tip under to lever them up, or else poke a screwdriver into where the valves are and lever in there. Be careful not to damage any sealing faces, or clean them up with a mill file if they do get damaged. You'll probably be able to hear the valves leaking as you turn the motor over, or feel a lack of compression and vacuum.. A compression test won't work because the inlet valves won't open to let air in, but if you turn it by hand there will be resistance of some sort, either as vacuum develops or compression develops. You could also check the valve clearances before pulling the cam cover off. . Bent valves hold the valve open and they have too much valve clearance. If you can't decide whether the valves are bent or not, you could either put the chain and cover back on and then do a compression test, or, just pull the head off and invert it and fill the combustion chamber with fuel.. it shouldn't leak out of the inlet or exhaust..

Ha.. That's a strange one.. And is probably a pointer to what's at fault.. but I haven't figured what .. It's possible that that behavior is caused by the brake lights effecting the electrical system.. Perhaps if you try it with the brakes on but after disconnecting the brake switches wiring... It might lead us somewhere. The other thing that should probably be checked is the fuel pressure..

Nah I got it wrong.. it was a 450 that had the different settings. A wrong plug can give those first symptoms you mentioned, but not generally the second cold start thing.. The plug with the wrong settings causes the problem because efi leans out the mixture when it's on a light fixed throttle, and then the spark struggles to ignite the fuel while it's weak. When the motor's cold though it should be getting a lot of fuel, and even a fairly wide gapped plug should work fine.. It is probably running lean all the time, not just at light throttle and speed. .. Have you taken the plug out and checked if it's white ? If it has vacuum hoses you should check them for splits.. I'll keep reading..

I'd say that if anything was going to help it would be an injector cleaner product. I'm in New Zealand though and don't know seafoam or probably any of the products you might use.. We don't seem to have much trouble with our fuel here.. perhaps it's because we don't have the freezing conditions you do in some parts over there. The only additive we use here is for diesel.. Gw sounds like he's used some of the fuel additives..

Oh. Those are different symptoms to what you first mentioned.. not unrelated though I think. I'm not familiar with Polaris so I'll have to go read the manual.. haha. Do you happen to know whether this has a cable throttle or an electrically operated throttle down on the engine ? Just so I'm reading about the right thing. It sounds like it's too lean, which they always are when you cruise along with a fixed throttle and light load, but that cutting out when cold sounds like really lean.. Injector cleaner might help, but only if the injectors are gummed up from stale fuel or sitting for a long time unused. If it misfires when you are riding at fixed throttle and moderate loads, but doesn't set the dash flashing or anything, or set any trouble codes, I'd be suspecting a wrongly set sparkplug, an air leak into the inlet manifold or some small vacuum hose somewhere.. Maybe a tight valve.. That's what I'd be checking first.. but I'm a mechanic.. Try the fuel additive, it's easy and won't do any harm, and it might cure it.. Let us know if it doesn't.

I think it will be lucky if the symptoms, which sound quite pronounced, go away with an injector clean or a decarbon.. It would be interesting to know how quickly these symptoms came on, and what the circumstances were.. And what model this is exactly..

There are lots for the yfp350.. that would probably do for most jobs, just some of the specs would probably be different.

You need to check the valves aren't leaking after you get the cam out.. They can get bent when a chain comes off.. on some vehicles. Neither the cam nor the chain will be holding the cam/head cover on.. It will just be the dowels and the sealant.. if you are sure you got all the bolts out..

The cam cover is that top piece of/on the head assembly, it has the valve covers bolted to it. They might call it a head cover or something.. There are a couple of dowels locating the cam cover, they will be tight probably and hindering the cover lifting off. You might have to find somewhere to lever the cover up a little..

Are you sure your spark plug is good and set to the right gap ? That can cause symptoms like you describe. So will the ignition timing being too advanced.

To just change the chain alone I think you'll be able to take the cam cover off, cam out, and the side cover and stator flywheel etc off, then by rotating the chain when looking from above, that is, swing the front throw of chain out away from the bike, so it'll swing around the end of the crank, and then haul it upwards. If you need to change the timing chain and slipper I think it may be necessary to take the head off.

Yup.. Sure sounds like it. Once you take the valve/cam cover off you will see if the chain's off or broken.

Yeah, that's the tricky part.. haha. In the old 12v systems there was more resistance in the primary windings and you could tell which was which with an ohm gauge. The cdi coils have so little primary resistance in the primary that it would need a very accurate ohm gauge, or an oscilloscope.. I don't know how you are going to tell the difference, but I'll bet that's the problem.. That or a bad earth which has much the same effect on the coil.. If all three of the coils you've had have been aftermarket, perhaps it's time to invest in a genuine item.. If some of them have been genuine yamaha, then check the earths.

It can be that even though the test readings are right, if the insulation is not good enough to prevent the HT breaching it, then the coil can still not work.. Depends where the actual breach of the insulation occurs..

As for having the coil either way around.. That's not so. The primary and the secondary windings both attach to the same internal earth. If it's connected the wrong way around the HT instead of earthing straight to that internal earth, has to go through the primary windings to get to earth.. That HT burns through the insulation on the windings. It has to have the internal earth end of the primary windings going to earth..

If it was totally open circuit you should have got the infinity reading same as you do when the leads aren't attached to anything. You could use a test light and a battery to test/confirm the primary.. It should have the test light burning brightly, as bright as straight across the battery.

And contact cleaner really isn't enough.. You should very carefully pull the switch apart, making sure the tiny springs and ball bearings in there don't get lost, (do it over a catch tray), and give the contacts a good rub with something like a steel wool or scotchbrite..

When you pull start it, and it's running, do the dash lights or headlights work then ? And if you give the start button a quick push while it's running, does the starter work ?

Never seen a twin Briggs.. very cool. The sort of thing my son would like.. He's got a bit of a vintage engine collection.

So, is this a no crank problem, or a cranking but no start problem ? And if cleaning the switch contacts the other day gave a temporary cure, why haven't you recleaned the contacts ?

Have you rechecked the switch contacts ? The contact cleaner might have left them too clean and they might have got corrosion .

View File 2010 Kymco MXU450i Service Manual 2010-MXU450i Submitter Mech Submitted 02/21/2023 Category Kymco ATV  

Haha.. I must be a lucky guy. I signed out and came back and browsed all over as a guest and only got one small square in the center of the screen, which I clicked away.. I'm on linux.. perhaps that makes a difference..

I'm on a pc Kibble. The difference though will be that I contributed to the running of this site a while back, because it is a good one. I contributed when I found out it was only two guys running it.. We all see things differently though and how we see things is how they are for us.. Contribute a few bucks and enjoy the site.. Or not. But don't let it make you bitter..