I have a 2005 400EX. It has only been riden once. I did an oil change after that and it has been sitting in the garage for a few months. I start it every now and again to keep the battery charged. I went out today to start it and its matching twin. One Honda started up decently, the other would not start at all. After a while, I got it to kick over. Now, it idels rough and will only idle for about ten seconds or so, then it kills. If i give it throttle, it will run, but will backfire as i let off.

The Honda is completely stock. No jetting or anything...just factory.

Any suggestions????

 

Sounds like the idle jet is clogged. Almost bet it is. Take carb off and bottom bowl and pull the jets out and blow them out. Should run fine. The idle jet is the one beside the one in the very center.

 

It that very difficult to do. I am actually pretty handy, just haven't done this before.

 

No, it's quite easy. First, turn off the gas and then loosen clamps at front and back of carb. There are rubber boots the clamps go around. Pull the carb. from boots. There will be two cables in the top of carb. It is not necessary to remove. You can remove bottom bowl while carb is still attached. Take 4 bottom screws out of bottom bowl. Gas will run out. Take bowl off. You will see the main jet in center(It will have a screwdriver slot on it) Theirs a plastic piece that will come off, note how it comes off. Off to the side of main jet, there is sometimes a rubber plug. Pull it out if there is one. You will see a small screwdriver(flat) crew inside hole' Be careful and make a solid turn out. Unscrew both jets since you have open. Be careful of the main jet, the needle is inside this jet. Blow them out and put them back in. Put plastic piece back in and then bowl back on. Also, put an inline filter on also.

 

Okay...so I did as you said. I pulled the two jets and blew them out. Should i have seen anything? I cannot start it, because as i was taking the carb out, i noticed that the screw on the front clamp was all stripped. I had to drill it, and I have another clamp on order.

I will try to run it as soon as the new clamp comes.

 

I should have told you to see if you could blow through small jet with your mouth to see if it was stopped up. The hole is so small you wouldn't see anything blow out with compressed air. Make sure you put a small inline filter on gas line, this will help future problems. Your bike sitting so long allowed dirt in gas to settle in jets and stop up.( You might already have filter,I'm just assuming). If this doesn't help. I'll assist you on taking carb completely off and cleaning entire carb. Your air=mixture screw could be stopped up also. But backfiring on decceleration is usually idle jet stopped up. You can try to start bike up without the clamp being real tight just to see if it idles but don't ride it.

 

Okay....i took the bowl off, and removed the two jets, and blew through them. They did not seem too clogged. I put the carb back on today, and same thing...idle is very rough and began backfiring.

I took the carb off again, and double checked the jets...they seem okay.

I started to disassemble the carb to look for any obvious gunk or clogs. I took off the valve assembly (black pastic deal) and attempted to blow into or suck on the various tubes. I noticed that the tube on the exterior, which a hose attaches to, I cannot blow or suck. I don't know if this is normal, or something might be clogging it.

 

Update....

Took the Carb apart...checked for gunk or clogs...none found. Blew out hoses and jets. Replaced spark plug. Bike started right up...but after it warmed up, would not idle. Kills pretty quickly. Doesn't seem to be backfiring yet, but definitely won't idle.

Are there any adjustments to be made to the carb at this point?

 

Yes, there is a idle adjustment on side of carb. Should be able to turn screw sticking out of the side with fingers or screwdriver/ clockwise. Sounds like your on the right track. Also on your bike, the idle adjustment might be a flexible spring looking thing with a **** on the end. Turn that ****. I don't know why this would be happening if the bike ran fine before.

 

Well, I rode it around the block, and it seems to ride okay now. It is even idling with the idle adjustment screw turned down pretty far. What i was wondering was where the mixture adjustment screw is. I still think it might be running a little rich. If it is the screw i think it is, i will not be able to adjust it with the carb in place. The only screw I can see is a flat head screw, recessed on the bottom of the carb, directly in front of where the bowl meets the carb body. Is that it? and if I have to adjust it with the carb off, how do i know how to adjust it?