Stumble/miss just off idle then surge

[jdoorn14]

I think I've got something strange going on with my '07 (~6200 miles) and I'm hoping you all can weigh in and either reinforce my thoughts or steer me in the proper direction.

He starts with no problems usually full choke to begin, but dialed back fairly quickly to keep between 3000-4000 rpm. Once the engine warms nicely (5-10 minutes), I get a somewhat strange response to input at throttle when the engine is still in neutral. If I slowly open the throttle from idle to 1500-2000 rpm, it seems to pop/stumble/miss a couple times. As it does this, the rpms drop a little. If I crack the throttle just wide enough to hit 2000 rpm, I will get the stumble/pop/miss, then the rpm will surge from 2000 to 4000 rpm with no further movement in the throttle.

I took a video this afternoon just after changing the spark plugs from the original to new Iridium. Also took pics of the old spark plugs.

Just looking for thoughts on what I should be looking at first.


Video available here:

Plug Pics:

Left (Clutch side)








Right (Brake side)

[Big Rich]

The difference in plugs kinda surprises me. Any modifications to intake / exhaust / jetting? Just curious.

I can't comment on the video, but from looking at the plugs I would say your float levels aren't identical for some reason.

[jdoorn14]

Nothing has been done to intake/exhaust/jetting since I've owned it aside from just blowing out the stock air filter.

Also notable is this is a fresh tank of gas with about 35 or so miles into the tank of gas.


Sent from my iPhone using Tapatalk

[Big Rich]

Ok. First thing I would do is check your float level with the clear tube method.

Forgive me for not watching the video btw. But is the bike on the kickstand or center stand when testing? If it's on the kickstand, gas might be naturally running to the left carb instead of the right.

[bombsquad83]

The carbs definitely need a little tuning.  I would check the float height as Rich said first, then check for an air leak on the right side.  If those look ok, then I would move on to the mixture screws and make sure they are turned out the same amount.  If all of that checks out ok, then maybe a full carb clean. 

Also, have you ever checked your valves?  Mine had about the same mileage when I got it as you, and it ran smoother once I swapped valve shims.

[jdoorn14]

The bike is on the center stand for this testing in the video. I first noticed it as I was warming it up on the side stand though. It's also been funky at slow speeds when taking off from a stop (stalls really easy). Thought it was just my lack of clutch technique, but maybe carbs could be partial cause?

I haven't checked the valves either and I'm thinking it's coming up on needing that too.


Sent from my iPhone using Tapatalk

[Cincykz]

Hi all
I just created a new thread about my issue. My bike does the same thing. Identical. Did you ever resolve this?

[mrdrprof]

My 06 had this issue. I gave my carbs a very thorough cleaning and my floats were also not adjusted right. Strangely, the little rubber cap for the port you use to sync the carbs was missing. This was when I just got my bike so I guess the previous owner didn't really know what he was doing haha. If that is missing, it can create a vacuum leak and make the bike run weird. I just took a small piece of rubber tubing and put a screw in it to plug it up. I'm not sure which one was the main issue but that's what I did to fix mine. You should also check to see if the rubber boots are seated properly both on the airbox and on the engine/carbs. Also make sure they're in good shape and not broken anywhere.

[Cincykz]

You know, I think my vacuum port is plugged, but now you've got me wondering.....
Carbs are pretty clean, and I just put in new needles and seats, and I believe my floats are set right.... Clear hose shows the level maybe one mm above gasket level, if even.  I will double check for my vacuum port.

Thanks for the reply