Low Rpm Stumbles and Dies.....Any ideas?

Hi All, I have a 2008 Suzuki DRZ400 with 12000kms, It has a full FMF Q4 Exhaust and the 3x3 Mod and the JD jetting kit. I have had it for a couple weeks now and has been running great up until last weekend. I was riding along when suddenly the engine sputtered and died. It fired right up again and I was able to make it another 15 miles before it died again. then again after about 5 miles. This only seemed to happen when the RPM was just off of idle. Higher RPM's still work great. It starts and idles just fine but if I blip the throttle the engine will stumble and die. I dont think this would be a jetting issue because nothing has changed since I bought the machine but now the problem is very obvious. I took the carb out, cleaned it with carb cleaner, reassembled, and still the exact same problem, low Rpm stumble and die. Is there anything mechanical that could cause this? something electrical? It has gotten slightly colder outside over the last couple weeks but jetting wouldn't be that sensitive would it? Any help is appreciated!!

Also forgot to mention that it is the DRZ400S model with Mikuni Carb.

 

I had a similar problem right when I bought my bike.  It would die when I blipped the throttle.  Raised the idle.  No more problem.

While idling, see if the petcock is wet.  If so, either fix the vacuum petcock or change to a raptor

Which pilot jet are you running? I think one larger worked best for me, (1,100')

Turn the idle speed up a bit also. You did say it quits only at idle, right?

 I could try and turn up the idle but like I said it worked great a couple weeks ago at the current idle speed. This is definitely a problem that has developed rather than just a miss adjusted carb.The carb is set at:

 

Pilot-25

Main-155

Blue needle in 3 position (1 up from the bottom)

 

Does this seem right? I'm at about 850'.

Set your idle to 1800 RPM'S. 

 I could try and turn up the idle but like I said it worked great a couple weeks ago at the current idle speed. This is definitely a problem that has developed rather than just a miss adjusted carb.The carb is set at:

 

Pilot-25

Main-155

Blue needle in 3 position (1 up from the bottom)

 

Does this seem right? I'm at about 850'.

 

I know, it seems too easy.  I did all the same things you did when I got my bike.  It was doing the same thing to me when I got it.  At the time it only had a full pipe installed.  I did the 3x3 and a JD kit.  Cleaned the carb inside and out.  I was convinced that these mods would fix it.  I am also running the exact same jet set up at 1100'.  Got it all buttoned back up after the mods and it was still doing the same thing!  

 

Turning up the idle was the answer.  I haven't had a single stall since.  Going from a low idle to a much higher one was a little odd at first.  Seems like the engine is revving way too high at idle, but I got used to it.  Best of all no more stalling in traffic.  Try the idle first.

If your idle sounds like a UH-1E main rotor, it's a bit low.

Hi All, I took the carb apart last night. I found that the small plastic piece that holds the needle in place in the slide had come loose causing the needle to bounce around inside the carb. when I took it apart the small spring directly above the needle was completely out of place and caught in the bigger spring further up the slide. Once assembled again correctly the hesitation is gone. Thanks for the input everybody!!! 

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