Hi everyone, my new to me 2012 is finally ready to be modded. I removed the front end, rear end, inspected and re-greased all the bearings, checked the calipers, pads, serviced the suspension, new tires (Kenda Trackmaster 110/100/18 and Shinko Fatty 90/100/21), so now it's time for the MCM mod, the FMF Q4, and the DJ 2152 kit with the lidless setup with a Moose air filter. Other than the Kouba, what air/fuel adjustment screws are available?

Thanks, Mike

 

Mike, you did not mention getting a performance pilot jet.
Some may consider a larger pilot jet optional, it is not.
It is simply "part of the process" when installing a performance setup in a CVK..
A #40 pilot jet (or #38 if you are never below 3000 ft ASL) should never be overlooked.
The stock #35 does not offer a sufficient range of fuel adjustment, making the Kouba Screw ineffective and a waste of money.
Those that do not include this "step" (in their performance setup modding) simply don't know what they don't know - and what they don't know is what they are missing out on performance-wise !

For extreme penny pinchers, a pilot jet could be considered a good first mod on a dead stock bike.

I do not know of any other fuel screw options..

 

Can you clarify the performance gains with a larger pilot jet if the optimum 'best / highest idle' is at, for example in my case, 2 turns out on the stock 35 size? The bike is snappier off idle with this pilot in my case than the larger 38. I think it would be good for fresh modders to understand what a larger pilot may or not do for them. I'm at around 2800 ft ASL and typically ride higher elevations.

 

Oops-yes-upon your advice earlier I did get the 38 and a 40. I just forgot to mention that. I have been real busy getting this bike up to my standards from a maintenance baseline. I always put reliability first.

 

A larger pilot jet creates a richer Air Fuel mixture (AF) within the pilot system. The pilot jet constantly creates this AF and it is distributed to the engine through the idle fueling port (whose actual output to the engine is controlled by the fuel screw) and the transfer ports between the butterfly valve and the slide. The transfer ports output are not adjustable. These ports simulate an accelerator-pump-like "shot of fuel" whenever the throttle is opened. So, the idle fueling is unaffected by a larger pilot jet (once the fuel screw is readjusted) but the "pump shot" is made richer.

For bikes running lidless setups, MCM, or both - as the OP of this thread - the larger pilot jet becomes even more important for max performance increase.

I assume you are recalling memories of when your bike was a stockbore running the stock CVK - at any rate, I have no idea why your perception "is what it is".
What I mean is that there are many possible scenarios whereby your #35 could "feel better" than a #38 - damaged fuel screw, damaged seating (fuel screw seating) , partially clogged/obstructed/missing aeration pin holes on your #35, previous owner mods on the #35, etc etc..

 

"Idle fueling is unaffected by a larger pilot jet"

Seriously? Can you point to documentation on this because it is contrary to everything I've read and been told.

 

Yes seriously.
You don't need documentation to understand this - just as you don't need documentation to understand that 1+1=2..

Close the fuel screw and the engine dies due to fuel starvation - regardless of which pilot jet is being used.
With a #40, open the fuel screw too much and the engine labors under a "too rich" condition at idle.
The #40 allows full control of idle fueling - from too lean to too rich ..

By manipulating the fuel screw, YOU control idle fueling, regardless of the pilot jet size. In this regard, a larger pilot jet does not affect idle fueling, you do.

However, the way I worded the statement, one may think that larger pilot jets can be installed without concern for readjusting the fuel screw. I will edit to be more informative..

 

It's pretty awesome how you understand this and no-one else gets it.

With a 40 pilot jet (maybe even the 38, I don't remember), I couldn't get the bike to die from fuel starvation buy seating the fuel screw.

What are some indications of a lean pilot jet and/or screw setting?

• If your air screw is in further than 1 turn, you need a richer pilot.
• If your fuel screw is out further than 3 turns, you need a richer pilot.
• Off idle hesitation or bog.
• Revving the engine in neutral will result in hanging RPM’s, or RPM’s will slowly drop back to idle RPM.

What are some indications of a rich pilot jet and/or screw setting?

• If your air screw is out further than 2.5 turns, you need a leaner pilot.
• If your fuel screw is in further than 2 turns, you need a leaner pilot.
• Off idle heavy feel or sputter.
• Revving the engine in neutral will result in RPM dip below idle RPM, RPM’s will drop quickly.
• Turning the fuel screw all the way in will not stall the engine.

How do you properly adjust a pilot air/fuel screw?

The proper way to tune a fuel/air screw is to make adjustments on a fully warmed up engine and at LOW RPM. Lightly seat the fuel/air screw and set to factory settings as a baseline. With engine running at low RPM, turn the screw in clockwise until the engine begins to stumble, then turn the screw counterclockwise until the engine stumbles, noting how many turns in/out both occurred. Now, adjust between these two settings to achieve highest RPM and smoothest running engine. Reset idle to recommended settings and test ride motorcycle. If engine bogs or hesitates during acceleration, richen idle screws 1/4 to 1/2 turn and see if that helps. Rev engine in neutral and note how RPM’s return to idle. If RPM’s hang, richen the mix. If they dip below idle, lean the mix.



Source (and there's many more like it. I can't find any source that recommends installing an over-sized pilot jet to gain pumper carb response): https://www.howtomotorcyclerepair.co...rew-explained/

 

I said previously that I had no idea why your experience is what it is - now I have a pretty good idea.

If you could not kill your KLX by closing the fuel screw, you had a problem somewhere within the "fuel screw apparatus" whereby you were unable to actually close off the idle fueling port via a fuel screw.. Or you had any one of a number of other carb faults that would allow fuel to enter the carb barrel from other ports/orifices..

The CVK does not and cannot offer (Quote: "to gain pumper carb response"...
The transfer ports DO offer a simulation of a pumper carb shot when the throttle is cracked open. Which applies strong vacuum signalling to these ports before the slide lifts.
This "simulation" does not offer the same "jolt" as an actual accelerator pump shot (therefore not the same as a "pumper carb response"), and I have never said or hinted that it would - perhaps you should not read more into my statements than what I actually say.

What I do say is that the richer "simulated pumper shot" from a bigger pilot jet will enhance the rider experience thru better throttle response..

 

As to why it seems to you that I am the only one that knows this stuff - I can't answer that.. Try calling Harley tuners and ask them what the transfer ports do on a CV carb. If you find one that says they supply a "chunk" / "jolt" of fuel to allow the transition (transfer) from the pilot system to the main fueling system, you can then ask them what the effect would be of increasing the fuel "jolt" delivered by the ports.. If they say "oh you mean by a larger pilot jet" , yep that can "wake up" your throttle response..

Then you can answer your own question - That there IS someone else that "gets it"..

If it turns out that I am awesome - as you can't find any other CV carb peeps that know this stuff - I won't let it go to my head..