Honda NX4 sudden engine problem... carb? dirty fuel?

[Gerd]

Hello all
Im the happy owner of a 2010 Honda NX4 Falcon, a brazilian made dual sport with an engine based on the XR 400's. The carb is an original japanese Keihin. the bike looks something like this:
It's given me several thousand trouble-free miles (with the exception of a dead battery on it's second year). Last week I took it to the dealer (official Honda service and all) where they did the usual oil change, air filter, valve adjustment and general revision. It worked great for a week until yesterday, when it died on me while on my way to work.

It happened on a slight donwhill, where i coasted for just a second before crossing a ditch, and the engine died. I pulled over, tried to start it, nothing. Tried again with a WOT, and it sputters and starts, only revving normally if I keep it above 3000 rpm or so.

Right now the only way to keep the engine running is to twist the throttle a bit, or use the choke. But the bike will not idle, it just dies. It felt to me like lack of air, but I checked the filter and it is brand new. The most annoying thing is that it happened all of a sudden, so something must be blocked or broken. The electrical system is okay, and the tank is full of gas.

I´m quite handy with wrenching, but I dont want to touch that carb.... at least not before you guys tell me waht may be happening here...

Thanks...

[indr]

Maybe try running some Seafoam mixed in with the fuel.

[Gerd]

No Sea Foam available around here but will try some other fuel aditive... Any idea on possible causes? Dirt in fuel maybe?

[GSAragazzi]

Something similar happened to me with my thumper. Died after 10 minutes of great performance. When it did I pressed nd pressed the magic button and nothing. I waited a few minutes and it started but it was coughing and as soon as I rev it, it died. Well, my solution was a technical tap (let her fall). I pushed her over on to the grass ( with yours I woud slowly lay it down). Well, whatever was messing with the carb cleared bc as soon as I got it upright it fired and I cruised home very smoothly. I did add Seafoam when I got home and allowed her to idle a bit.
I get you cant get Seafoam, try Techron.
Let us know if this does the tick.
Good luck
Cheers

[qkenf4u]

did you fill the tank RECENTLY ? WATER in the float bowl/gas ? (its a HUGE PROBLEM here in AZ)

[JALnSC]

Drain about a cup of gas out the carb bleed screw.

[Gerd]

Ok people
I took the carb apart and reassembled it without problems, a feat of wich I'm extremely proud , and
found out the origin of my no-idling:

My air screw fell out.

With the carb apart, I gave both main and pilot jets a good bath in carb cleaner, and also cleaned some fuel goo from various other carb areas. When the time came to check the air mix screw, I noticed something odd:



According to my little research, this happens sometimes, especially to mx racers
So, tomorrow I will go to my Honda dealer (in another country, go figure) and order the tiny parts: screw, spring, washer and o-ring. Murphy's Law seems to be playing an important role in my life experiences!

Thanks for the help, and give your opinion on how likely this is to happen...

[ExTex]

If it happened once, it may again,
So order 2 of each part so you will have a spare.

Ride Safely.

PS Nice looking bike!

[Gerd]

Originally Posted by indr

Maybe try running some Seafoam mixed in with the fuel.

Originally Posted by GSAragazzi

I get you cant get Seafoam, try Techron.Let us know if this does the trick.

I finally found an equivalent carb cleaner, and will also use it in the tank when I finally put the bike together, thanks for the tip.

Originally Posted by qkenf4u

did you fill the tank RECENTLY ? WATER in the float bowl/gas ? (its a HUGE PROBLEM here in AZ)

Yes, tank full of fresh gas. The petcock comes with a water-trap, sort of. I´m gonna install an inline filer anyway, just to be sure.

Originally Posted by ExTex

PS Nice looking bike!

Thanks!

[PeterW]

Put a small dab of silicone at the end of the air screw hole once it's reassembled and adjusted.

Not enough to plug the hole, just enough to part cover the hole and stop the screw backing all the way out. If you need to remove the air screw it'll scrape off.

Pete

[Gerd]

Ok guys I got an aftermarket carb repair kit and installed the new fuel screw and assorted bits. Now my bike is back to normal!

Even better actually, because now with the proper carb adjustment the bike is no longer running rich (looking back, it definitely was just before the screw fell out). So thanks you all for the input!