400ex ??

[zach R 7x]

I just bought a 2000 400ex. It is totally stock. It has been sitting for 3-4 yrs , stored inside but still sitting without being started. I cleaned out old fuel, pulled carb, cleaned, changed oil and new plug and air filter. It runs and starts right up but when warm, it is making a pop noise through the aair box. I found the intake boot was broke and replaced it. It still makes the popping noise when warm, plus wont idle. Runs great other than that.
I am asumming it is running lean, but before it got put in storage it ran fine and never did this. Can the valves just need adjusted? Any info would be much appriciated!

[storms400ex]

Sounds like the pilot jet is clogged

[zach R 7x]

I am going to order a kit to rebuild the carb, hopefull that is it. thanks for the help.

[on the rocks]

sounds like the valves. after sitting that long in one position the springs will weaken from being compressed so long. could try to adjust valves but it sounds to me like the valve springs are junk.

[DragonGunner]

When you cleaned the carb did you take apart the accelerater pump? It has a black liner thingy in it...if you didn't you need to do this, you will find dryed gas junk in there that needs cleaned....also did you take out the air mixture screw completely an clean.....an did you use Carb cleaner? I'm amazed how many of my friends say they cleaned their carb....with air, instead of carb cleaner.

[zach R 7x]

I did not pull carb all the way apart and clean. I actually talked to a friend and he told me the same thing you did DG. Tonight I plan on removing it and doing a total clean up. I am also going to check valves. Figured it won't hurt. Does anybody know the clearences? It so, please let me know, it would save some time looking it up on the web somewhere.

[BlasterEaten250]

Sounds to me like your carb just needs to be gone through. But the clearances are .004 intake and .005 exhaust.

[kt1148]

Originally posted by zach R 7x
I did not pull carb all the way apart and clean. I actually talked to a friend and he told me the same thing you did DG. Tonight I plan on removing it and doing a total clean up. I am also going to check valves. Figured it won't hurt. Does anybody know the clearences? It so, please let me know, it would save some time looking it up on the web somewhere. Here you go...http://www.atvriders.com/articles/valveadjustment400ex.html

[zach R 7x]

Thanks for the info guys. I won't get a chance to work on it till Sunday, let ya know what I come up with....

[zach R 7x]

Hey guys, tore down the carb, adj the valves ( weren't out adj.) put it back together and it still does it. Thinkin now that it may need new valve springs. Any other suggestions before I spend the coin for springs?

[DragonGunner]

Save your coin, valve springs ain't going to have a thing to do with it. Wish I could be there an see what its doing an play with the carb myself.

[yelian103]

Get a rebuild kit and replace everything especially the pilot screw o-rings. Mine did the same thing and it turned out to be the pilot screw o-rings. Go up a size on the pilot jet.

[Crosshairs]

Originally posted by zach R 7x
Hey guys, tore down the carb, adj the valves ( weren't out adj.) put it back together and it still does it. Thinkin now that it may need new valve springs. Any other suggestions before I spend the coin for springs?

did you replace the pilot jet?, they are very hard to clean, so there is a good chance its still clogged...your symptoms really sound like a clogged pilot circuit...I doubt very much its valve springs.

[storms400ex]

^ x2

[red200040ex]

I would even replace the current pilot jet with a 42 size and adjust the pilot screw accordingly.

[zach R 7x]

The carb actually looked pretty damn good. I pullled both jets and cleaned, I could see daylight through the pilot so assumed it was good to go.

What it is basically doing is back firing through the carb and won't idle at all. before I tore the carb apart it only did it at idle or low rpm, now it is doing it all the time. High and low rpm. I checked for air leaks on the carb and intake boots and found none. Even pulled that plunger boot apart and it looked like new. To me this seems to be more than a carb problem. Thus the valve questions....

[zach R 7x]

Where is the best place to buy Honda parts without breaking the bank? online or dealership?

I'm just gonna purchase a carb kit and start there....

[Thumpin440ex]

Originally posted by on the rocks
sounds like the valves. after sitting that long in one position the springs will weaken from being compressed so long. could try to adjust valves but it sounds to me like the valve springs are junk.



If you have went and taken care of all the other possible things, this is where I would look also. Sitting with out running or being cycled will weaken the springs for sure.

John

[zach R 7x]

Ok, finally got the time to work on this quad. I replaced the springs, seals, keepers and gaskets along with lapping the valves and clean up.

Put it all back together with ease and it still does the same thing. Exactly the same thing....

I also pulled the carb totally apart and cleaned everything, even took torch tips through jets and they were clear.

I pulled the plug to look to see if it was rich or lean and it was coated black! Also blowing mixture of white and black smoke out of the exaust . White when at a idle and when you stab the gas, it turns black. Not horrible , but noticable.

I am going to get new jets, but I know their open, so don't think that is what it can be.

Please guys... anymore suggestions??

[Rip_Tear]

Do you have any kind of exhaust, air filter or any kind of modification to this 400ex? Has it ever had any mod or been changed in any way?

I'm thinking it did or does and you needed to rejet from the start.

[zach R 7x]

Rip, the motor is completely stock , piston and rings were replaced but all stock parts put back in. Very little hours put on the newer top end.

I got this from one of my best friends and he bought brand new. It has sat for several years because he just didn't have the time to ride it anymore. It ran fine before it sat.

I have main jets for this , just don't have any pilots. Should I buy a certain pilot jet or just buy several and adjust? Should I go up or down?

[DragonGunner]

If you see daylight in your jets I would say they are ok...I want to know about your air mixture screw......Did you take it all the way out with the spring and carb clean inside that spot. Then put back, and how many turn out from bottom is it set......we will go from there. Good ideal to go up a size on pilot, will start easier when cold.


I would like to know the size of the main jet since you had it out also.


Your plug is showing rich.....get rid of that plug and try a brand new one...let me know what that does....was it dry black or wet black?

[zach R 7x]

Gunner, I'll have these answers for you on saturday. Thanks for the help!

[zach R 7x]

Well, I got her runnin smooth again today!!

Buddy of nine came over and we messed with it all day. What we really found out was the motor was really getting hot and hot fast. I found some bigger jets and installled and this cooled the engine down somewhat, then we pulled the top end down and retimed the cam and found it was a tooth off. Put it back together and it ran 95% better, rejetted again and it smoothed right out, engine wasn't running hot anymore and backfire went away!! Hooray!! lol

Not sure if when the guy put the new piston in installed it off , because I put it back in as I took it apart. But it works now!

Thanks for all the help guys...