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TOPIC: 36mm Keihin Pilot Screw: How many turns?

36mm Keihin Pilot Screw: How many turns? 14 Nov 2011 16:00 #488457

  • mwriders
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Cleaning and refitting a pair of Keihin 36mm CV carburetors for my '80 KZ440B1. The shop manual is specific about how far to open the pilot screw for non-US models (2-3/4 turns). but for US models, the book only says to count the turns when removing the pilot screw and to reinstall it in the same position. The problem is that somebody has been inside these carbs before I got there and has done a pretty sorry job of rebuilding them (unwound springs, gaskets instead of'O' rings, bent linkages, etc.). So, I have no idea if they were installed correctly in the first place.

Anybody know the answer to this one? How many turns for the pilot screws on Keihin 36mm CV carbs?

The attachments are the two items from the shop manual.




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1980 Kawasaki KZ440B (brand new eBaby)
1998 Ducati 900S (gone)
1978 BMW R100S (gone, damn it)
1975 Yamaha RD350 cafe (gone)
1986 Yamaha XJ650 Seca (gone)
1981 Kawasaki KZ440LTD (gone)
1969 HD Sportster (gone :)
1966 Honda CB160 (gone, damn it)
1965 Suzuki 80

36mm Keihin Pilot Screw: How many turns? 16 Nov 2011 14:07 #488785

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C'mon, somebody knows the answer to this. Somebody with a happily running 440 LTD, maybe? I'm just looking for a starting point before I install those pilot screw hole plugs and adjustments become difficult. Maybe I should start at 2-3/4 turns and see what happens?

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1980 Kawasaki KZ440B (brand new eBaby)
1998 Ducati 900S (gone)
1978 BMW R100S (gone, damn it)
1975 Yamaha RD350 cafe (gone)
1986 Yamaha XJ650 Seca (gone)
1981 Kawasaki KZ440LTD (gone)
1969 HD Sportster (gone :)
1966 Honda CB160 (gone, damn it)
1965 Suzuki 80

36mm Keihin Pilot Screw: How many turns? 16 Nov 2011 14:17 #488787

  • Patton
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Pods or air box?

Good Fortune! :)

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Last Edit: by Patton.

36mm Keihin Pilot Screw: How many turns? 16 Nov 2011 14:35 #488792

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Air box, carefully reconstructed, with a stock filter.

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1980 Kawasaki KZ440B (brand new eBaby)
1998 Ducati 900S (gone)
1978 BMW R100S (gone, damn it)
1975 Yamaha RD350 cafe (gone)
1986 Yamaha XJ650 Seca (gone)
1981 Kawasaki KZ440LTD (gone)
1969 HD Sportster (gone :)
1966 Honda CB160 (gone, damn it)
1965 Suzuki 80

36mm Keihin Pilot Screw: How many turns? 16 Nov 2011 14:38 #488794

  • Motor Head
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mwriders wrote: C'mon, somebody knows the answer to this. Somebody with a happily running 440 LTD, maybe? I'm just looking for a starting point before I install those pilot screw hole plugs and adjustments become difficult. Maybe I should start at 2-3/4 turns and see what happens?

Forget the Little plus, get the bike to run, and then set the Screws for the best Idle and performance.

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1982 KZ1000LTD K2 Vance & Hines 4-1 ACCEL COILS Added Vetter fairing & Bags. FOX Racing rear Shocks, Braced Swing-arm, Fork Brace, Progressive Fork Springs RT Gold Emulators, APE Valve Springs, 1166 Big Bore kit, RS34's, GPZ cams.
1980 KZ550LTD C1 Stock SOLD Miss it
1979 MAZDA RX7 in the works, 13B...

36mm Keihin Pilot Screw: How many turns? 16 Nov 2011 14:58 #488799

  • Patton
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Would begin fine tuning carb pilot circuits with pilot screws set at 2 1/2 turns out from lightly seated, which is an arbitrary ball-park setting, and should be suitable from which to continue fine tuning by achieving the best steady idle by further adjusting each pilot screw as the thumb-screw idle position is gradually lowered with idle rpm being maintained by adjustments of the pilot screws.

If the idle speed rpm isn't affected by turning the pilot screw, there's likely something wrong inside the carb, such as an obstructed pilot circuit passage.

There is nothing magic about the beginning position of the pilot screws so long as they are set where the engine will run, to thereby enable fine tuning from such setting.

Usually, the best engine running final position of the pilot screws is different from where they started. But the best ultimate idle position will be the same, regardless of whether the screws started out at 2 1/4 or 2 1/2 or 2 3/4 or whatever.

Even if the FSM specified a specific beginning position for the mysteriously omitted number of turns out from lightly seated on some particular model, it's merely a suggested starting position for purposes of further tuning (and turning).

Good Fortune! :)

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36mm Keihin Pilot Screw: How many turns? 16 Nov 2011 17:01 #488808

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Usually, the best engine running final position of the pilot screws is different from where they started. But the best ultimate idle position will be the same, regardless of whether the screws started out at 2 1/4 or 2 1/2 or 2 3/4 or whatever.

Even if the FSM specified a specific beginning position for the mysteriously omitted number of turns out from lightly seated on some particular model, it's merely a suggested starting position for purposes of further tuning (and turning).

Good Fortune! :)[/quote]

Perfect. That's the advice I needed. That and Motor Head's advice to not sweat the little plug. Thanks, Patton and Motor Head.

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1980 Kawasaki KZ440B (brand new eBaby)
1998 Ducati 900S (gone)
1978 BMW R100S (gone, damn it)
1975 Yamaha RD350 cafe (gone)
1986 Yamaha XJ650 Seca (gone)
1981 Kawasaki KZ440LTD (gone)
1969 HD Sportster (gone :)
1966 Honda CB160 (gone, damn it)
1965 Suzuki 80

36mm Keihin Pilot Screw: How many turns? 17 Nov 2011 00:05 #488855

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And just to clarify --- the best idle often results with the pilot screws being in slightly different positions.

For example (using arbitrary figures), the best idle on a twin cylinder dual carb system might be achieved with one pilot screw being at 21 /2 turns out and the other pilot screw being at 21 /4 turns out.

For another example, the best idle on a four cylinder four carb system might be achieved with #1 pilot screw 21 /4 turns out, #2 pilot 23 /4 turns out, #3 pilot 23 /16 turns out, and #4 pilot 25 /16 .

Upon achieving the best idle, I have by then usually lost sight of exactly where each screw adjustment is in relation to fractional turns out or in from lightly seated.

Good Fortune! :)

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Last Edit: by Patton.

36mm Keihin Pilot Screw: How many turns? 23 Nov 2011 10:16 #489818

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Use the manual setting as a starting point only. If you have access to an exhaust gas analyzer, set the carbon monoxide to 2-3% and the lowest hydrocarbon setting. The other way is called a lean idle drop. I am assuming that you have already synchronized the carbs, if not, do that first or you are wasting time.Starting with the screws 3-4 turns out, turn the mixture screws to the leaner settings untill you hear the idle slightly drop. Then reverse about 1/8-1/4 turn. That should be real close.

TJ Jackson EastSide Performance Motorcycles

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