I had the problem of the engine running well at first, with normal power and smooth operation, including when accelerating at slow speed in third gear. When the engine had warmed up a little, it did not run smoothly at low speed, and did not have as much power.

It had been necessary to set the mechanical idling adjustment high to keep the engine from stalling when warm. Eventually I found that three of the cylinders were not supplying any power at idling when the engine was warm. I did this by grounding each spark plug to see whether or not the engine slowed down.

Then I checked the clearance of the valves (with the engine cold), and I found that there was practically no clearance for the exhaust valves of these three cylinders. I adjusted them to proper clearance. The engine now runs properly both cold and warm, and the engine slows down a little when each spark plug is grounded, showing that all the cylinders are working at idling.

I had the problem of the engine running well at first, with normal power and smooth operation, including when accelerating at slow speed in third gear. When the engine had warmed up a little, it did not run smoothly at low speed, and did not have as much power.

It had been necessary to set the mechanical idling adjustment high to keep the engine from stalling when warm. Eventually I found that three of the cylinders were not supplying any power at idling when the engine was warm. I did this by grounding each spark plug to see whether or not the engine slowed down.

Then I checked the clearance of the valves (with the engine cold), and I found that there was practically no clearance for the exhaust valves of these three cylinders. I adjusted them to proper clearance. The engine now runs properly both cold and warm, and the engine slows down a little when each spark plug is grounded, showing that all the cylinders are working at idling.

Could be an out of adjustment or stuck anti-percolator valve on the carburetor, allowing the float bowl to pressurize when hot and percolating raw gas down the jets, fouling the plugs....

Also check that your heat riser is opening as it warms up, and not stuck shut, overheating the intake manifold and percolating the fuel in the float bowl of the carburetor.

I seam to remember an old Hudson Guy from years past telling me that he drilled very small holes in to the top of the float bowl lid to relieve the pressure of percolating fuel.
Any one heard of this or have done this?

I have drilled a 1/8 inch hole in the top of the float chamber on my 1935 Hudson 8 carburetor, but for a different reason: to fill the float chamber, using gasoline in a squirt can, when the car has been sitting a long time. I did it many years ago and it has not caused me any problems.
My car hasn't had flooding problems, however I installed a hand choke when I first got the car, since the automatic choke wasn't working and I like to control the choke.

Couple of things to check.
1. Make sure you don't have a tight intake valve like I had on my Commadore.. Very little clearance when cold and when it warmed up the valve wouldn't close at all. Messes the whole intake system up.

2. I had stumbling problems over about 30 mph with an 8. Drove me nuts. Finally traced it to the aftermarket wire between the points and the case having too large a wire contact. When the breaker plate rotated it shorted. Trimmed the large end on the wire and that fixed it.

You have 2 problems, tight valves and the carb is not set correctly, You must use the carter tools to set the carb by the manual. set the valves cool using my specs, intake .011", exhaust .013" this is for todays gas, as it is made to run hot. You must use new feeler gauges, not the ones that were used to do with a running engine as they are pounded out of specs. Walt Mordenti.

[quote="Walt and Margaret Mordenti" post=9019]You have 2 problems, tight valves and the carb is not set correctly, You must use the carter tools to set the carb by the manual. set the valves cool using my specs, intake .011", exhaust .013" this is for todays gas, as it is made to run hot. You must use new feeler gauges, not the ones that were used to do with a running engine as they are pounded out of specs. Walt Mordenti.

Sorry to drag up an old post. Walt can you confirm the above valve settings? I'm looking for cold settings but there are a lot of different clearances mentioned during my searches.
Cheers Simon

Set them as I said. Today's gas is made to run hot so you need a little extra clearance. This is not 1948. Just make sure you do the settings after the car sets overnight and do not start the engine. Also in your carb you have to make sure your ANTI-PERCOLATOR valves are opening when engine is idling. Also metering rods are set to specs. Walt.

Scott Ambler. I see this all the time. People put electric pumps rather than rebuild the vacuum tank. The problem is the pressure exerted on the needle valve exceeds its design limitations when a pump is used.. When this happens, the valve won't modulate the bowl level properly. The float valve regulates the flow: not just turns it on and off. An accurate bowl level is needed to regulate the rich/lean mixture.
When the valve is overrun, the bowl level goes up and the motor runs rich.

I tell everyone to rebuild the Vac Tank, It is very easy to do and the tanks work very well, seldom needing any work for more years than the life expediency of the pump. Hopefully, the valve is OK and will need nothing more than a cleaning and seating to work well.

Odds are the valves are tight. When they are tight, especially after it is warmed up, it creates extra, unwanted pressure blowing back through the carb.and intake manifold. This causes all kinds of running issues once the engine is warmed up. Having just one tight valve causes most engines to have a nervous idle that you can't seem to adjust out. Having more than one usually causes the engine to lack proper performance, again especially when the engine is warmed up and hot. . You should plan on removing the valve covers, inspecting and adjusting the valve lash. When you are talking about splasher engines, there is so many things that can happen that cause running issues. Starting in the mid 30's, Hudson started using a thrust washer behind the cam. These fiber washers wear out and/or wear to nothing. With that said, if the valves were set correctly say 2000 miles prior to having any running issues, and then the engine slowly or all of the sudden starts running badly, the thrust washer could have broken and because the cam has a thrust button pushing it back, it has now pushed the cam back the thickness of the thrust washer, and at the same time has put the lifters and cam in positions that do NOT match for wear. The cam follower-[lifter] - had wear in the face that matched the cam. I know this sounds a little confusing, but when you adjusted or had the valves adjusted, you compensated for the wear pattern between the cam and lifter. When the cam gets moved back by the thrust washer missing and/or heavily worn and falling out, it puts the cam lobe in an area against the lifter that doesn't match, thus taking up any extra or adjusted valve lash. If you remove the lifter and lifter jacket, inspect the face of them, you can see where the lifter has wear on them wider than the cam lobe. This is where the thrust washer has worn thru time and the thrust button pushes it back as designed.

[quote="Michael Fox" post=2332]Hi All,

Recently I have been having problems with my 1948 Commodore 8 sedan running rough. I replaced the distributor cap, rotor, plug wires, plugs, and the carburetor has been rebuilt TWICE. When the car is first started, it runs well, as it warms up, it begins to idle roughly, and while being driven, as the car accelerates, it seems to "break up" as if misfiring, When I pull the plugs, they are BEYOND Black. I am becoming quite frusterated with the car...needless to say, the factory installed "Drive Master" works perfectly.... All input is appreciated!!!!!!

Hudsonly,
Mike Fox

Another possible problem that can occur as the engine warms up is valve clearance , not a nice problem to think about.