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KL convert to downdraft carb

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trebot
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KL convert to downdraft carb

Post by trebot » Thu Feb 25, 2021 11:37 am

Have a '56 KL with the stock updraft carb (263M). Rebuilt numerous times and still have stalling issue after about 1/4 mile at anything above 2000 rpm. Rebuilt fuel pump, ignition system with no change. I think maybe the carb is just wore out.
I've been researching downdraft carbs. I can flip intake manifold upside down and have a level carb mount surface. Found model Y100 at Carburetor Doctor. Handle to 300 c.i. motor and it's low profile (looks like a Holley) and has adjustable Hi speed jet.
Anybody have any experience with this type conversion?

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drrot
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Re: KL convert to downdraft carb

Post by drrot » Thu Feb 25, 2021 4:14 pm

Someone has tried something similar. This dual 2bbl for an M series came in some stuff I bought.
Have you sent your carb out and had it professionally done?
2x2mbl.jpg
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Jim Staib
www.finewoodboats.com


1947 Penn Yan 12' Cartopper WXH474611
1950 Chris-Craft 22' Sportsman U-22-1532
1957 Chris-Craft 26' Sea Skiff SK-26-515
1968 Century 17' Resorter FG-68-174

trebot
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Re: KL convert to downdraft carb

Post by trebot » Sat Feb 27, 2021 5:42 pm

Had carb rebuilt by Mark Edmundson here in Michigan. Ran great for 5 miles, then started acting up as before. Ever since, its been 1/4 mile, stall, starts right back up, 1/4 mile, stall.

Greg Wallace
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Re: KL convert to downdraft carb

Post by Greg Wallace » Sun Feb 28, 2021 9:04 am

Have you done any trouble shooting beyond the carb and fuel pump? Symptoms suggest ignition failure after warm up, or intermittent fuel supply interruption as possible areas of concern. Faulty coils and condenser may produce similar systems. An obstruction in bottom of fuel tank contacting stand pipe is another. I've encountered faulty ignition switches that cause similar symptoms. Does your system have a ballast resistor and does coil match up. I would start by eliminating ignition or fuel at point of failure. Not saying could not be carb but avoid tunnel vision your dignostics. Good luck
Greg Wallace 23 Custom 22166 former Chris-Craft dealer Russells Point, Oh.

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Bilge Rat
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Re: KL convert to downdraft carb

Post by Bilge Rat » Sun Feb 28, 2021 12:46 pm

I agree with Greg's recommendations but will add that maybe temporarily running it from a gas can, bypassing the boat's tank will eliminate everything with the tank and fuel pick up. I know that its tough to do while motoring across the water, but it can be done safely. The fuel pick up sometimes has a suction issue from a pinhole that can act up and cause mystery problems.
1966 Lyman Cruisette 25 foot "Serenity Now!"
1953 Chris Craft Sportsman 22 foot "Summerwind"

trebot
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Re: KL convert to downdraft carb

Post by trebot » Sun Feb 28, 2021 7:54 pm

First off, thanks for your responses. New things to try and check out. I had electronic ignition when motor first started acting up.
I changed over to points and new coil. Acted up exactly the same way. I'm gonna try the fuel tank elimination and a new ignition switch.
The sequence is this: Warm up motor, head out, get up to 2000, all's well, get over 2100 and she dies. If I pull the throttle quickly, she'll drop to idle, but doesn't stall, idles fine. My gut says it's the carb.

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