400ex eating spark plugs

[MotoMan]

Ever since the weather has turned cold, my 400 has been eating spark plugs. I have went thru 2 plugs in the last month (That's 2 more then I have in the entire life of the quad previously) and for the life of me I cannot figure out why. The plugs just stop working properly, they start to produce a yellowey weak spark AROUND the electorde instead of a sharp blue spark in the middle as they should, and eventually they will stop sparking alltogether (I would imagine they are sparking inside the plug like the electrode or ceramic had cracked inside, but not sure).

The jetting is spot on as far as I can tell. The vent hose for the tank is not plugged, gas is flowing freely, and the air filter is clean.

Anyone got any ideas what to look for? Could it be a batch of bad gas? CDI going bad? (Normaly they don't "Go bad" they just stop working)

Help please, I love riding the quad in the snow and we just got our first coat.

[Yardpro393]

something electrical for sure.

[TexTwister 393]

Sounds like a week coil or pickup coil..

[MotoMan]

I am going to run some electrical tests tomorrow. I was hoping that someone had heard of this before on a 400 and knew right off what it was.

One other thing I forgot to add. It ALWAYS happens when starting on a cold day for the first time. Never when the quad is warm or has been started that day already.

I have a meter and a manual, I will run some tests tomorrow keep shooting ideas my way guys.

[MATTXR250R]

Jim I have heard ALOT of 400ex owners say they had this problem...They said on a cold day when they went to start it for the 1st time it would foul the plug even though they had the jetting right on. I think the 400ex is just really cold blooded. I am not sure it is electrical. I have just heard of alot of people having that problem.

[MotoMan]

That's encouraging news actually Matt. That means someone has a solution for it somewhere.

[MATTXR250R]

I am trying to find an answer for you Jim...In the meantime IMO I think it would be very wise for you to check out [Only registered and activated users can see links. ].

I think you can look through the forums without being a member and might can use the search function to find some info on that..thats the site i heard of people having this problem on..Go to forums on the left side and click Honda on next page. Good Luck Buddy

[MotoMan]

I will check it out.

Thanks Matt!

[CRacer]

If it is electrical it could be the spark plug cap. If it is an '01 it may be a time for a replacement. Take the spark plug cap off the spark plug and see if you can twist it around on the spark plug wire. If you can then that is probably the problem. You should be able to twist the spark plug cap on the spark plug wire until it tightens up and stops. The bike is not producing enough spark to burn the gas/oil mixture which gets onto your spark plug which immediately fouls your plug, which I'm sure you already know. Same thing happened to my CR, got a new spark plug cap off the dennis kirk and had no more problems. Also, check your kill switch to make sure that isn't killing your spark. Could possibly be a bad coil, but very doubtful that it is your CDI. Maybe they are just cold blooded as Matt said, I'm just trying to toss around ideas.

[MATTXR250R]

Anytime Jim...I did a search there about your problem but it didn't return any results....You could sign up and just copy your post you did here and paste it there and see what they say

[MATTXR250R]

TTRRacer that could very well be the problem. Nice thinking. I have heard that the 400ex's are really cold blooded..I know the Honda Ranchers have a little heating coil thing in the float bowl of the carb if I am not mistaken that helps with starting on a very cold day. Maybe the 400ex could use one?

[MotoMan]

I will run some tests tomorrow TTR, and that will be the first one.

Thanks guys and keep the ideas coming.

[CRacer]

Cool, I hope it works out for ya.

[MotoMan]

Well, after running all kinds of tests (Everyone in the book plus the plug cap) and everything turning out normal, me about pulling my hair out and Bill running to a local shop to see if they had any spark plugs, (Thanks Bill!! ) I was about ready to torch the stupid thing.

I decided to wire wheel the spark plug and see what happened. Now keep in mind before I tried this I had NO spark in the plug whatsoever. Well I cleaned it up and layed it on the side of the head, and volia! I had spark. I also in the meantime drained all the gas out of the tank as it was a few weeks old. (The quad doesn't get ridden all that much) I put everything back together, filled it up with new gas and to my surprise, it fired right up and ran perfect.

Now it was warm today, around 45 at the peak of the day, but I still don't understand the plug thing that is just weird. We will see what happens the next cold day, but for now, it seams to be fine. :

Odd.

[FFRacing11x]

Try this..unscrew the sparkplug cap and trim the hi tension lead back about 1/4" and screw the cap back on...put a little dab of dielectric grease on the end of the plug wire first. This is one of the first areas to go bad as corrosion will set in and you have a bad connection. TW

[Rockey]

Sounds as simple as bad gas, feels good to figure it out!

[FFRacing11x]

How would bad gas affect the color of the spark?

[Rockey]

That I couldnt tell you, but stranger things have happened I guess.

[MotoMan]

Thats what I couldn't figure out FFR, how in the world would gas do that, unless the plug was somehow fouled or something??

If it happens again I will try your idea with the wire, I had the cap off today and looked in there, it seamed very clean to the naked eye, but you never know.

[FFRacing11x]

Sometimes trimming back the plug wire a scosh just gives the threads in the plug cap a new "bite". First thing I check with an ignition problem, with the kill switch the second. I always look for the easy things first. I try to use dielectric grease on all my electrical connections. Keeps out the moisture and inhibits corrosion. Good luck! TW