FCR - Blip, Blip, Dead. Help!

I have a brand new KTM 625 SXC with an FCR carb. I am running the OBEKN needle at #6, 175 Main, and 45 Slow Jet. I have the fuel screw out 1.5 - 2.0. Sea level.

My problem is I get the idle properly, and it seems ok. When I go ride, within a minute or two, the engine will die when off the throttle and never start. Fouled. So then I cleaned the plug, chenged to a leaner 42 pilot and went to number 5 on the needle. Again, its idling fine. While standing still, I blip the throttle twice about 1/3 - 1/2 - dies. Won't start.

I would think with the settings I have, that it would at least run. Maybe not perfectly, but it flat out dies and I can't even go out to test the settings to fine tune them.

What would cause this throttle blip to kill the engine and foul the plug? I am leaning toward the accelerator pump, but its all factory settings. I am thinking that I should put back the original pilot, main, and needle, but everyone says it is so lean that it is dangerous.

Help! I can't ride!


Sounds like the AP is dousing the fire. Check your squirt duration.

I would go back to stock jetting and try a richer pilot 48 and look in the bottom of the float bowl and if you have a leak jet pull it out and silver solder it shut or buy a 35 or 40 leak jet. Lean bog is usually the cause of the stall and flat bog when riding. That is why the FCR carb has the AP squirt in the first place. Usually too lean on most bikes.

I am already back to the stock idle jet, I think I may go back to stock everything and start over. However, I never rode the bike on the stock settings, so I don't know if it ever worked - I had no idea I would run into these issues.

This bike is brand new and I haven't even ridden it yet (I bought the bike way out of state since it was the last one on the east coast basically, so I can't exactly go back to the dealer).

Well, if anything, I'll learn something. So I need to first go and attempt to stare down the throttle body and measure the squirt. I've read the numerous FAQs about the AP and mods. I thought if I soldered the leak jet, that all the fuel would go to the throttle body and make it richer - correct? I thought the symptoms I had was perhaps TOO much fuel, which is causing the plug to foul. Blocking the leak jet would make it richer, right?


Sounds like you're on the right track. You will know for sure what to do once you've measured your squirt duration.

Hard to believe though that the AP is killing the bike though, unless something weird is going on. Are you using good fuel? Could the pilot air jet or main air jet be clogged? Did you put a freshly oiled filter in it and then ride it right away? Sometimes the fresh filter oil hasn't set yet, and it plugs the air jets. Keep digging, and let us know what you find.

This bike is brand new, so it shouldn't have any clogged jets or anything. The filter is new, although it certainly needs oil - it is dry. Fuel - well, it came from the dealer, so who knows how long it was sitting there. Maybe I should drain it and put in a known fuel? This is going to be a weekend project I see...

Yeah, I've never seen a bike die like this, but then again, I've only had sportbikes, never a big single.


sooty plug does not mean a thing when your motor dies and the fuel squirt soaks the plug! Try going richer first that is what is most sucessful with the leaned out stock settings. :naughty:

Yeah, unfortunately, I never ran the bike with the stock lean settings. I immediately put in a richer pilot, richer main, and a different needle, so who knows if this dying problem occurred stock. I went:

42 to a 45 pilot

168 to a 175 main

Can't remember old needle, but its now a OBEKN on clip 5 or 6.

People seem to report that these settings are a good place to start. Still, mine just flat out dies. Could it be operator error? Over zealous throttle before it warms up? This single just doesn't seem to behave like a carbeurated inline-4. I am going to clean the plug, warm it up slightly, pull away slowly, and put around for awhile. I want to see if it stays running. If I don't wack the throttle, I shouldn't have the AP going off too much. Lots of experimenting to do...


When you say it is to lean you mean the volume of the squirt? Not duration. correct?

By lean, I mean all circuits - pilot and main, are supposedly lean. It is recommended by most 625 LC4 riders to switch out the pilot jet, main jet, and needle for a some richer ones. Nobody has ever mentioned the AP on a 625, although it is the same FCR carb used on a lot of Japanese 4-stroke dirtbikes.

So is the AP the problem? Maybe, maybe not. :naughty:


I wouldn't automatically assume that no jets are clogged just because it is new. You might be ahead of the game if you clean the carb up anyway. Process of elimination.

Still can't believe the AP is responsible for the behaviour you describe, but I guess anything is possible. Have you checked your squirt duration yet?

Oh yeah, as far as the AP squirt is concerned, volume and duration are almost the same thing, unless your AP is just dribbling out, and that's a different problem all together.

My question was directed at IndyWR450's statement about the 48 pilot/leak jet.

Sorry MotoMike!

Barton - I can't imagine it the AP either, but I also can't imagine I could be having these problems with settings that a lot of other people are running successfully. Honestly, I am no carb expert, so I am looking at all possibilities. :naughty:

I won't have a big amount of time to look at this till this weekend. I will try a few things tonight, but measuring AP duration will be over the weekend.


:naughty: . No, wait - :D:D .

Ok, I am going to attempt to say this without looking like a fool...

1) I thought the fuel petcock was vaccuum operated.

2) There looked like there was plenty of fuel in the tank...

3) Everytime I took the tank off, messed with the carb, and put the tank back on, it would start and run. For awhile.

4) I had these stalling issues at the same exact time I started messing with the carb jets...

5) Ok fine, it was out of fuel.

The fuel tube in the tank is REALLY long. There looked to be plenty of fuel when I checked before, but apparently, it is not enough. I had the tank off and flipped it to Reserve, and fuel started pouring out. Not vaccuum operated. My theory is that everytime I took the tank off, fuel would slosh into that pickup tube, enough to start the bike and keep it running for over a minute. I assumed that the plug that I cleaned and the carb that I messed with made it run, but no, it was always sloshing fuel into that tube.

Well, as dumb as I feel, at least it works. The AP Squirt is 2 seconds by the way. Seems long, but at this point, I am just happy it runs. Also, I learned an awful lot about how the carb works, so I guess that is good.

Sometimes I look for the most complicated reasons for problems instead of the most obvious :naughty:

Name Witheld to protect the stupid

I'd laugh, but I've done stuff just as silly. Glad you got it figured out.

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