450i MXU Stalling

[Oldfriend]

I have a 2015 450i MXU. Its electronic fuel injected. After I’ve been riding for  20-30 minutes and stop, put it in neutral and then put it in drive or reverse, as soon as I touch the throttle it stalls like I’ve turned a switch off. It starts up again without a problem and will drive fine. It happens every once in a while. It will also sometimes do it if I let it idle for a long period of time around 45 or more minutes. I first noticed this happening when I was letting it idle to keep the battery charged over the winter.
I’ve changed the spark plug and put in fresh 91 octane gas and it still happens.
 
Any ideas would be greatly appreciated.
 

[Bratman2]

Probably not much help but it only calls for 87 octane. I would try that first. I have read were some complained about it fouling the plug if run pretty good and just letting off the throttle quickly. Might be a minor case of flooding. What plug did you use to replace the factory plug with?

[Oldfriend]

Thanks for the reply. I tried 87 octane first, then tried the 91 after someone suggested it. It does it with both. The plug I replaced was the one that the manual recommended, I don't recall the brand. The letting up on the throttle quickly and causing minor flooding is an interesting note. I believe it does do that.

[Bratman2]

I will make one more suggestion, which will not help your problem any, a battery charger. I use one for all my power equipment that sits for any length. I do not use a trickle charger as I believe they are bad for batteries over the long haul. Over the winter I will top off my zero turn, motorcycle, generator and anything else that has not run for a while with the charger. Maybe about every other month. Bike never sits that long though!  I also will charge them up some before cranking them up if they have sit for a while. Get one that backs out as they become fully charged. Reason being it is not good for the alternator to have to recharge a battery too many times.

I have tried "chopping" the throttle on mine just to see if it would seem to flood some. Sure seems like it does. I have not had mine to cut off though. More of a stumble when trying to take right back off. Mine is still fairly new with only 20 miles so far.  Are you still under warranty? Dealer close by? If so have them take a peek, can't hurt and might help someone else out too!

[Oldfriend]

I hear what your saying on using a charger. Problem is I don't have power on my property only a small generator. I may bring it home over the winter or maybe just the battery. I was also considering a solar trickle charger. It is under warrenty and I did have the dealer come to my house and take a look at it. He drove it around the block and said it was fine. Said I needed to drive it and not let it just sit and idle. Problem is I live in a city and can't drive it here. I bought it to keep on my property upstate which is 100 miles away. Intermittent problems like this are always an issue. Unless soemone sees the problem they tell you the can't do anything about it. Like I said it doesn't always do it. Drove it last weekend and it was fine. I only have 12 miles on it. I may call Kymco and talk to them.

One question though: you have a 2014 and it's EFI? I thought (could be wrong) that EFI was new for 2015?

[Bratman2]

Yes, my 2014 is fuel injected. Just got it recently as a left over in Va. It has right much more power it seems than our 2010 Yamaha Grizzly 450.  Hit 96 today so she did not move even though I was off work. I see what your saying about no power. Guess running it is your only option. Solar charger does sound like a decent idea. Sounds like you have a really good dealer, he does house calls! Sounds like a fueling issue that is sporadic at best. Similar to the running fairly hard and chopping the throttle closed. You would expect carb cert. machines to run on the lean side, maybe not. If I can every find were I read that about the plug, seems they replaced with a different plug that helped cure the problem, I will let you know. Keep me posted on how yours does and I will do the same. I drove a fairly good distance to buy mine so don't know how any local dealer would like me coming in for warranty work. Hopefully I won't have to!! I am fairly decent with a wrench. Sync the throttle bodies, valve adjustments and resetting the TPS with a laptop on my Moto Guzzi bike.

[Bratman2]

The MXU 450i is basically the same machine as the Arctic Cat 450 H1 and the 500 H1 at least runs the same drive train. Searching last night on some of the Arctic Cat forums produced mixed results. Here is the best I could figure out.
1. Some had the same problem and it disappeared after the unit broke in. Man, do I like the sound of that. So simple, just drive it. Never had any problem fixed so easy in my life, but you never know!!

2. A few found the idle set too low and raised it. Some raised the idle by adjusting the slack in the throttle cable adjuster. Some had to raise the idle at the throttle body itself because they ran out of adjustment at the throttle cable. I would be leery of adjusting the TB screw, I know on my Moto Guzzi it is factory set and is not suppose to be touched. That might result in warranty issues if the paint around the screw is broken, kind of a seal type dab of paint to show tapering has occurred.

3. A lesser few had to lower the idle some because the CVT clutch was still grabbing slightly. This was done at the throttle cable adjuster. I guess you would need a more accurate tach than factory to determine this. Seems I have a spare digital hour meter/tachometer that just hooks to the plug wire. I didn't pay a whole lot for it so you may could find one reasonable cheap and hook It up to see if high idle or low idle was your problem.

4. A couple claimed to have replaced the factory sparkplug with a NGK Iridium  (IX version) plug and that cured it.

5. I think I read were one or two claimed going up in heat range one on the sparkplug cured their stalling.

Number four surprises me a little. Iridium plugs only claim to fame are they last longer, nothing else. They do not burn hotter or colder, just longer life period. So with number 4 I wonder if it really was a matter of the machine actually breaking in around the same time they replaced the sparkplug. If yours is actually a rich condition, which I thinking chopping the throttle produces, no TB adjustment will cure that. I don't see how break in will either but there was quit a few that claimed it did.

For number five a hotter heat range plug you would step down one number. Our atv calls for a CR7E plug so you would want a CR6E if you wanted to try that. I don't know if our units come with NGK plugs (it does use a NGK number) but they are the ones I prefer to use, That seems likely a possible fix as lower speeds allow a plug to be slightly cooler and a slight richer fuel mixture could foul the plug under those conditions. Running the unit harder would clear out the fouling until the ideal condition (low speed, slightly rich) presented itself again.

For me I have not had my unit cut off yet so I am opting for paying more attention to hard running and coming off the throttle abruptly. As the miles and hours build if it continues to stumble I may opt for the hotter plug. My choice would be a NGK "racing" version CR6E, not the IX iridium plug. 

Best I can come up with after searching pretty hard. Hope that helps you some. Keep me posted if you cure it or it cures itself.

[Oldfriend]

Wow, thanks for your efforts! I tried some of these, sort of:

I adjusted the throttle cable to remove excessive slack but stopped short of increasing the idle. I read that your not suppose to do that, but I may try it now anyway.

I bought an Iridium plug months ago after reading it fixed some peoples problems , but haven't installed it. I'm going to try that too.

The dealer told me that if I drove it, it would be fine, I can only hope!

It will take a while to try these, as I mentioned I only drive it on the weekends because it's upstate 100 miles away.

Thanks again!

[Oldfriend]

Well I installed the irdium plug and have taken it on two rides so far and it hasn't stalled. I'm not prepared to say it's "fixed" because it didn't do it on every ride anyway. Stay tuned!

[Bratman2]

Interesting, I will stay tuned. Have 36 miles on mine as of yesterday. I am beginning to really like my Kymco.

[Oldfriend]

BTW, This is my first ATV. Other then the stallimg issue it's great. I didn't want to spend alot and they had 1.9 financing with a 3,000 lb winch! I got it in Camo it looks wicked cool! I'm thinking of changing the wheels and tires on it but 24" seems to be a problem to find. Do you think 25" with work? It sure seems to have enough room. I should probably start another thread for this.

[Bratman2]

Yes 25" will work. Our Grizzly 450 has 25" Duro tires on it. The day after I got it I swapped tires to just see if they would fit. I can assure you looking at it that 26" might be a problem. The Grizzly 450 is our first ATV, but we only got in January. I wanted a new one but most were so expensive. Wife almost had me talked into a new Polaris HO 400 left over. When I found out they were 48" wide I passed and went with the Grizzly due to the 43" width. I had just bought my grandson a used Kymco 90 also. Then I did some research and found a right nice assortment of ATVs made by Kymco. Then several weeks ago I found the 2014 MXU 450 leftover and heavily discounted and only 1/4" wider than the Grizzly. Mine is in black and for some weird reason has alloy wheels. It is not a special edition are anything. I started to ask when I went to pick it up but thought better of it. I bought mine in Virginia and live in North Carolina. It was well worth the trip. I thought I had taken some pictures with the 25" tires but can't seem to find them right now.

Okay, took some searching on another computer, lol!!

[Bratman2]

Here is mine with the factory alloys and stock 24" tires. Kind of puzzled about the alloys as to why they came on it and for basically free!!

[Oldfriend]

Thanks again! You've been a big help. If I could just feel cofident that the stalling isssue is resolved, I'd spring for the new wheels and tires. I tried to attach a photo, but they are all too big. I get one this weekend. BTW, I'm in New York.

[Bratman2]

You are welcome and glad I could help you out. Bet you have cured yours!! We seem to be part of a pretty small club, Kymco owners with a MXU 450. I kind of thought you were in New York state. We had friends when I was growing up long ago that lived in Fulton. They are the only people I ever heard say upstate, lol. I am in Eastern NC.  Imagine you have some nice riding up there. My 33 year old daughter is home from Denver. She has only rode an ATV once in her life, a vacation in Mexico a few years ago. Told me she didn't really care to try one again, ever. After much pressure she finally agreed to give it another shot. Parked mine with 43 miles now, we went over 6 miles with lots of narrow woods trails. Seems it runs better and better. I noticed hardily any stumbling at all now when the throttle is chopped abruptly. We switched up a for a couple of miles because I wanted a second opinion on the Kymco compared to the Grizzly. She pretty much mirrored what my review stated in the other post. More powerful, seemed to soak up bumps better, lighter steering and something I had failed to notice. Much better brakes. Helpful to get a second opinion sometimes.  Seems she had to ride some ratty gear shift atv that did not leave a lasting impression in Mexico, she thought they were all like that. She liked the Grizzly right much, but when she tried the Kymco she did not want to give it back, lol! To post pictures I had to use Windows Live Photo Gallery, then click edit, then resize "custom". Kept making it smaller until I got below the 192 kb. I was wrong about the tires being Duro, they are Maxxis but are 25's!