Hi Guys,

Im having a minor issues with the jetting (I think) on my bike and before I go making changes and testing I figured I would throw it out here and maybe you guru’s can assist so I don’t have to pull the carb 100 times to fix…

Basically Im getting a bit of surging/stumbling when cruising or slightly accelerating on or just above ¼ throttle. It seems to only happen as the RPM’s get up around the 5k – 6k mark and only in this throttle range.

At first I thought I had bad fuel or a blocked jet because I had been away and hadn’t ridden in about 10 weeks, but I pulled the carb, cleaned everything + fresh fuel and added an inline filter and it still does it.

I was thinking that it might be a little lean in this part throttle range but because I can’t remember it being like this before and now that it is warmer here it should actually be richer???

Can being to rich cause engine surge/stumbling?

Bike is an 06 with the 351cc kit (about 1000klms on the 351cc so far) with a TM36-68 at sea level and it’s about 30 – 32 degrees Celsius at the moment. Seems to run really well in all ranges but may be a little flat in the ¼ range.

• 17.5 pilot at 1 ¼ turn out (this is halfway between the rich and lean stumbles)
• Idles and starts fine
• P-6 needle jet
• 9EBY01-50 needle on the very bottom clip (richest needle, richest clip position)
• 135 main
• Pump pretty much starts straight away and finishes at ¾ throttle.

Im still thinking too rich but not sure if this can cause what im experiencing…

Thanks for your help guys.

 

This may NOT be a jetting problem. Look up the extra grounding wire that IDRIDR found caused a stumble/glitch at about those rpms. Ever since I added that particular extra ground, I found my clock keeps the correct time...before I added the extra ground, it would periodically, suddenly, change to the default 12:00! Don't know for certain if this fixed my clock, but, it has fixed a lot of people with a stumble/hesitation at about 5000 rpms.

 

Not me that found it, but remember reading about it. I think that ground issue was more prevalent on the 2009+ models.

 

Yes, a rich mixture can cause problems. Move the clip on the needle up a notch or two.
Do a spark plug mixture check.

Ride on
Brewster

 

Thanks guys, I read about the grounding issue but it didnt look like it was a problem on the 06's.

Thanks Brewster, that’s exactly what I was planning on doing. Plug also looks fine, not rich, it’s a light brown/tan colour on the insulator and the ground electrode is slightly black and is dry. I don’t really I trust plug readings though.

 

Isn't a marshmallow looking plug good? Idk... if feel plug readings are only good for extreme cases of rich/lean situations.

Wait, you quoted a little black on the electrode... so maybe a tad rich.

 

Ah! At least I wasn't giving you credit for something that didn't work!

And, you're correct, it is on the newer bikes. My bad x 2...