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KLC carb (Zenith 11168 / 552M) mix screw adjustment

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KLC carb (Zenith 11168 / 552M) mix screw adjustment

Post by [email protected] » Sun Sep 01, 2019 7:07 pm

Happy Labor Day all! I’m spending some of it tuning up my ’56 Holiday and could use some help. Thanks to a lot of good advice from these boards, I have my ignition dialed in. Now I'm on to the carb.

My carb is a Zenith 11168 (552M) on a KLC with idle and high-speed adjustment screws. It was rebuilt in 2008.

Can anyone share what the approximate settings for each of these screws are? I’m running rich, my wife isn’t enjoying our tuning runs as much as she once did, and knowing where to start would help!

Here’s what I’ve been able to read so far:

>> HIgh Speed Jet T Screw

Starting Point
I have no idea what the right high speed starting point is for this particular model.

The manual for the Zenith 550 series doesn’t say.

I've heard everything from 1 ½ turns out to 3 to 4 ½ or even 5.

The manual for the successor carb on the KLC (Zenith 11849/263M) says the T screw is only used for fuel conservation, and that for full power, it should be 5 turns out. Could that apply to mine?

In-water Tuning
Full Throttle, dial screw IN (leaner, I think) to Max RPM, then a quarter turn richer, which is OUT (I think).

>> Idle Screw

Starting Point

Manual says 1 turn. Have also heard 1 ¼ and 1 ½

In-water Tuning

At 300 RPM over spec idle (For KLC 650+300 = 950) dial OUT (Leaner according to the manual) go to max RPMs, then back IN ¼ richer.

For this screw IN is richer, cutting down air according to the manual.

* * *

I'd really appreciate some guidance on where this might off and any experience with this particular carb, where the lit is a little scarce.

Thanks in advance - even just knowing I have the in-water approach right would be a relief!

davidvn
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Re: KLC carb (Zenith 11168 / 552M) mix screw adjustment

Post by davidvn » Tue Sep 03, 2019 9:07 pm

A good starting point for the high speed adjustment is three turns out from fully closed. For the idle mixture screw one and a quarter turns out from fully closed is a good starting point Your engine should run well with these preliminary settings

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JimF
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Re: KLC carb (Zenith 11168 / 552M) mix screw adjustment

Post by JimF » Thu Sep 05, 2019 1:18 pm

My KLC carb (11849) has no high speed jet on the bottom. Just a large brass nut or plug. I haven't taken it out. Am I in trouble? I am having trouble getting it to run after a total engine rebuild including carb over haul.There are possibly other issues.
1930 Chris-Craft Model 100 20' "MOXIE"
1935 Chris-Craft Deluxe Utility 18' "ALICE K II"
1940 Chris-Craft Red and White 25' "Old Paint"
1946 Chris-Craft Sportsman 25' "CinCity"

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Bilge Rat
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Re: KLC carb (Zenith 11168 / 552M) mix screw adjustment

Post by Bilge Rat » Thu Sep 05, 2019 2:12 pm

The fixed type high speed jet was "optimized" for maximum performance and if everything else is working correctly (and the carb is clean!) should work well.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

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Re: KLC carb (Zenith 11168 / 552M) mix screw adjustment

Post by [email protected] » Thu Sep 05, 2019 2:40 pm

JimF, As BilgeRat says, this is in the 11849 manual: https://www.dropbox.com/s/0di6eslf3mzuted/IMG_0748.jpg

Seems like the high speed jet screw was added to some of the 11849's as an option to reduce fuel use, but should be left wide open for max power, which is presumably what you get with no screw at all. Never a bad thing! :)

And thanks for the reply DVN!

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