RuthlessButcher

Now I don't know that much about carbs but from what I understand is the Main or Pilot jet fuels the carbs at low RPM and the secondary jet is either added or replaces the main jet at higher RPM. Now my question is does anyone know at how many RPM they switch. I`m trying to diagnose a hestitation at between 4 thousand and 5 thousand RPM when getting hard on the gas. I`m wondering if a needle or slide are sticking or perhaps this is normal. I just got my VTR in February so I`m full of questions still.

Circuit_Burner

Pilot jets are for idle and up to 1/4 throttle. But the overlap starts at around 1/8 throttle, and its effect on 1/4 throttle openings are minimal.
Needle hight (clip) and needle profile generally control a wider range in the middle, overlapping with the secondary jets (if they have them) and the mains, which govern fuel delivery starting(taper) at around 2/3 throttle and taking control mainly in the upper throttle openings.

If needles or slides are sticky, it can be felt when moving the CV plungers with your hand, and also visual inspection.

RuthlessButcher

I should have mentioned that the bike should be all stock except the K&N Filter. I say should because when I got the bike it suffered from a serious flat spot between three and 4 thousand RPM. The previous owner performed a bafflectomy and installed a dynojet kit and the Ducati dealer I bought it from replaced the cans with stocks and were supposed to stock the carbs but I remember the tech saying he could leave the jet or jets in but blamed the steep taper on the dynojet needle for the flat spot which I hated because I ride with my kids on the back and it always chugged in mid corner.

Circuit_Burner

Try the stock air cleaner element, if it clears up, you know what direction to go.
K&N filters only produce a wide powerband when jetting is just right ( which it rarely is )
I ran headers, 2 bros cans, cam profile mods, jetting kits ... with a stock filter.
Runs best here where Im at with the stock filter.

Tweety

The K&N filter needs jetting changes, otherwise it produces a big hole in the powerband, not an increase at all... And stumbles at around where you are experiencing them...

If you want too keep the K&N (for cleaning&re-cycling) you can try adding in the plastic lip that the stock filter has and see if that helps... I'm trying that right now... and it seems to be better... But at this point that is subjective "seat of the pants" feel...

RuthlessButcher

right on thanks for the info. I think I will pick up a stock filter from what I hear it runs smoother and tourqier

Gregw

Hi Tweety,
Do you have a picture of that lip (and/or dimensions)? I bought my bike with the K&N so I don't know what the stock filter looks like. Thanks.

VTRsurfer

+1
I tried a K&N in my CX500 with 2 into 1 exhaust 25+ years ago. It lost midrange punch, so I went back to the stock air filter 1 week later.

Tweety

There is some info/link to pics here...
https://www.superhawkforum.com/forum...3Bn+filter+mod
https://www.superhawkforum.com/forum...amp%3Bn+filter

Gregw

Thanks Tweety,
Makes me wonder if an air dam below the filter might help, placed between the velocity stacks. That might keep the two cylinders from playing tug-o-war with the air.

RuthlessButcher

I saw BMC makes air filters like K&N has anyone seen one to see if it has the Fin like a stocker?

LineArrayNut

my BMC street (not installed) doesn't have fin

shayne

Sounds like you need to understand how your carbs work. Factory Pro have a very good section on CV carbs, so have a read of their hard work.

http://www.factorypro.com/tech_tunin...m_engines.html