Mikuni RS Flat Slide Pilot Adjustment Screws

Keep in mind that although the pilot circuit continues to provide whatever its ratio of air/fuel mix is throughout the entire throttle/slide movement. It just has the greatest effect at idle and just off of idle.

The accelerator pump does add fuel but only once you open up the throttle/slide. When you open up the throttle off of idle a lean mix occurs due to the increase in air flow, the pump adds fuel to help overcome this.

As an aside you can usually tell which type of screw you have by its location and by its tip. Air screws are on the air side of the carb (usually) and have a more blunt end to them. Pilot (fuel) screws are located on the engine side of the carb (usually) and have a very sharp tip.

gd4now wrote: Keep in mind that although the pilot circuit continues to provide whatever its ratio of air/fuel mix is throughout the entire throttle/slide movement. It just has the greatest effect at idle and just off of idle.

The accelerator pump does add fuel but only once you open up the throttle/slide. When you open up the throttle off of idle a lean mix occurs due to the increase in air flow, the pump adds fuel to help overcome this.

As an aside you can usually tell which type of screw you have by its location and by its tip. Air screws are on the air side of the carb (usually) and have a more blunt end to them. Pilot (fuel) screws are located on the engine side of the carb (usually) and have a very sharp tip.

Mikuni recommends the accelerator system be set to start pumping fuel at 1/4 throttle and end at 3/4, but by having it adjustable those settings can be varied considerably, or it can be completely disabled by simply removing the plunger rod.

After changing to the significantly leaner main and pilot jets, I'm happy to report that the engine likes it. Really thought there would be lots of pop,sputter, and backfire, but so far there is none of that...:woohoo:
I have the pilot fuel screws adjusted within the specified range, and the spark plugs have acquired the highly-prized but elusive "peanut butter" coloration after a hundred-plus miles of the varied types of riding I enjoy.

Thanks again SWest, for that delectable spark plug color description, which somehow I was able to find again.
Now I am going to "ride the piss out of it!"

Current RS34 Flat Slide jetting and carburetor settings:

Main Jets: 125
Pilot Jets: 117.5
Pilot Air Jets: 0.8
Pilot Fuel Screws: 3/8 to 1/2 turns
Accel Pump: 1/4 to 3/4
Middle (3rd.) needle clip position

I know...just leave it alone and ride. :whistle:

That is great news Dave,

I'll be using your set up as baseline on my first attempt with the 38's! Please post a good pic of the plugs when you can.

Thanks,

-Scott

Just got back from the high desert around noon. 90 up there, 110 down here. Felt like a blast furnace coming through the pass. I didn't put in the smaller jets up there and when I was getting off the FWY I was getting that popping sound as if it had leaned out. About 250 miles since I put in the larger main jets. I'll check the plugs this evening after it cools off. Just goes to show not to jump around. Had I put in the 55's it might have been too lean for 100 miles.:ohmy:
I'll post my findings in my thread.
Steve

SWest wrote: Just got back from the high desert around noon. 90 up there, 110 down here. Felt like a blast furnace coming through the pass. I didn't put in the smaller jets up there and when I was getting off the FWY I was getting that popping sound as if it had leaned out. About 250 miles since I put in the larger main jets. I'll check the plugs this evening after it cools off. Just goes to show not to jump around. Had I put in the 55's it might have been too lean for 100 miles.:ohmy:
I'll post my findings in my thread.
Steve

Been jumping all over the place, but going to 125 from 132.5, and 17.5 from 22.5 at the same time, was a complete shot in the dark...for me. :whistle:
Best jump yet! Risky, but well-worth the try considering the result.

Be cool



Corrected!

Are you sure it's not 17.5 pilots?
Steve

SWest wrote: Are you sure it's not 17.5 pilots?
Steve

Right you are!
Corrected...thanks again Steve

Kray-Z wrote: That is great news Dave,

I'll be using your set up as baseline on my first attempt with the 38's! Please post a good pic of the plugs when you can.

Thanks,

-Scott

Pics per request...

How do these look for color?



and...


:woohoo:

Damn those look spot - on! I can't say I've seen better KZ plugs. I'm going out in a while to check the GPz1100 DFI plugs to compare those, but yours will be tough to beat. Thanks to Dave and Steve for clarifying the 17.5 pilot jets, too!

-Scott

Gettin there even with the crap gas.
Steve

Kray-Z wrote: Damn those look spot - on! I can't say I've seen better KZ plugs. I'm going out in a while to check the GPz1100 DFI plugs to compare those, but yours will be tough to beat. Thanks to Dave and Steve for clarifying the 17.5 pilot jets, too!

-Scott

Thanks Scott, I'm pleasantly befuddled by the result. Had 0.9 air jets in there and was slightly lean, so the 0.8 went in and is much better. Can't imagine it being rich now, but...


Simple mods as follows: Stock 84 ZN/ZX head, 84 ZX cams/sprockets, V&H Street header/baffle w/no-wrap, Dyna 2000, RS34 carbs w/70mm. stacks fed by widened and gutted air box.

SWest wrote: Gettin there even with the crap gas.
Steve

Should I be satisfied, and just ride the piss out of it?

For good measure...