Flathead boggs down

Rick Leavitt

Rick Leavitt

Member
Hopefully someone can point me in the right direction. I had just rebuilt my carburetor because 1941 Merc flathead. It was bogging down when I accelerated. The jets were clogged up so I cleaned everything up and rebuilt it. Ran great for about 20 minutes. It started to get a very loud whistling sound. I discovered that the silencer was cracked. I found a replacement and installed it. Again the car ran great. I drove it around for about 10 miles and it started to bog down again when I pushed the pedal, it would idol very fine. now I'm getting a sucking / whistling sound from inside the carb. Gas tank is clean, fuel filter is clean. I removed the air cleaner to look inside the carb and the jets are working fine. It runs fine until she is really warmed up than bam sucking sound and motor bogging down. I'm completely lost. I checked the vacuum with a Vacuum gauge and she holds steady, no jumping around. Any suggestions????
 
The power valve would make sense. That was the only part that I couldn't replace. The one that came with the rebuild kit didn't fit, wrong size threads. I cleaned up the old one, but I bet it's bad.
 
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If power valve is leaking, bowl will drain all fuel from the fuel bowl down into the intake, then into any pistons where the intake valves are open, and then potentially into the oil pan. Ask me how I know…
 
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I just pulled the carb and removed the old power valve. The new one is completely different, much longer and the design is different. Is this a upgrade to the power valve or is it the wrong part?
 
Call Daytona Parts or check out their website at daytonaparts.com for a replacement power valve.
 
Try loosening the gas cap when it starts to run bad. That will check for a plugged vent. I only saw it one time in my 30-year-old history as a mechanic but it's something you can check for free. You could also take a can of carb cleaner and as it's running bad give it light squirt and see if it straightens out or gets worse. You're trying to figure out if it's a fuel of ignition problem. I've even taken a can of gas with a hose stuck inside the car with me, plugged off the hose from the tank and went for a drive to see if the problem lies in the lines and the tank. At this point it could be all kinds of stuff, you have to narrow it down to fuel of ignition.
 
A lot of 94 rebuild kits come with both a "Power" valve ("Economizer" valve) and a "Spark Control Valve" used only on the later model carbs. They look a LOT alike but function differently. I think the one on the left is a "Spark Valve".
 
There is a “well known” issue with these “new” power valves. It has to do with a radius at the base of the stem. Due to this radius, the gasket cannot sit properly and seal. Looking at the red gasket on the power valve in the left pic, it seems to be “floating” off the base. Certainly, the newer power valve has that infamous radius, and as such, will not seal.
 

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Ziggster said:
There is a “well known” issue with these “new” power valves. It has to do with a radius at the base of the stem. Due to this radius, the gasket cannot sit properly and seal. Looking at the red gasket on the power valve in the left pic, it seems to be “floating” off the base. Certainly, the newer power valve has that infamous radius, and as such, will not seal.
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Don't you guys know about "Spark Control Valves"? They mount on the outside of the later model 2100's and 2110's. Most rebuild kit suppliers include both valves in their kits. The Spark valves even have the same threads as the power valves and screw into the power valve hole. The serve completely different purposes and are not interchangeable.

He's got the wrong part. https://www.fordbarn.com/forum/showthread.php?t=241429
 
I’ve heard of spark valves, but don’t think I’ve ever seen one. Checked out your link, then went into the stash of my Holley 94 orig parts. Found a valve that looks identical to your #8 sample. Pretty sure mine is a power valve though as none of my Holley 94s have a port for the spark valve that I’m aware of.
 

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Some better pics of the “standard” power valve that comes in most all rebuild kits. I got the “correct” power valves with the radius machined off from Charlie at Vintage Speed.
 

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But they come with almost all rebuild kits today, and screw right into the power valve hole. Just because he (or you) doesn't have a place to put one doesn't mean he (or you) doesn't have one. They are VERY easy to mix up. I think that's what happened here if I'm reading his pictures correctly. The way to tell them apart is to suck on 'em from the large end and cover the hole with your tongue; if they hold vacuum, they're good power valves.
 
Ziggster said:
I’ve heard of spark valves, but don’t think I’ve ever seen one. Checked out your link, then went into the stash of my Holley 94 orig parts. Found a valve that looks identical to your #8 sample. Pretty sure mine is a power valve though as none of my Holley 94s have a port for the spark valve that I’m aware of.
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