Packard Forum Index » Pre-War (1899-1942)

Hello -
I'm working on a 1937 120C and it appears that the fuel is boiling in the sight glass of the fuel filter. The carb is hot to the touch. Has anyone seen a problem like this before?
Its the Stromberg, it does have a insulator gasket at the base of the carb. Gasket, insulator, gasket arrangement.
Car starts and runs, but after 10 minutes or so the carb is hot to he touch and I am essentially in vapor lock and the car will not accelerate and then will die.
My next step is to remove the intake and exhaust manifolds and investigate the interface between the two. It appears that there is a gasket between them.

I have never seen a carb so hot to the touch.
Thanks

Check the manifold heat riser valve, it's in the exhaust manifold directly below the carburetor. It's intended to divert hot exhaust gas to the base of the carburetor during cold weather warm ups to aid fuel vaporization but as the engine warms it should open and allow the exhaust gases a direct outlet to the header pipe. Yours might be frozen in the closed position? The counterweight should move freely up and down if the valve is not frozen. When the counterweight in the up position the exhaust gases are being directed to the hot box below the carburetor; the bimetallic spiral thermostatic spring unwinds as it gets warm, allowing the counterweight to drop and redirect the exhaust gases away from the carburetor base.

Vegas odds are 100:1 that O_D is correct.

I was looking for the spring or pin for the flapper, but not being intimately familiar with Packards I couldn't find anything that resembled what I was looking for.

It appears that this car was restored sometime long ago. The intake and exhaust manifolds are powder coated black. I don't see a thermo spring anywhere. It was removed on purpose I'm guessing.

Where would it be located? Photos perhaps somewhere around?

Thanks!

Someone else may steer you to pix, i'm sure there are some on this forum that you could find via the Search tool, but Packard's heat riser didn't change much over the years and isn't much different than other makes. I don't recall if it's illustrated in the 1937 shop manual but there is an illustration in the 48-54 parts list which you can view here.

As I recall there have also been some instances where walls separating the exhaust passages above the riser valve have eroded and a large hole formed allowing exhaust to enter the heat box even if the heat riser flapper valve is functional.

Here is a photo with a typical layout. Weight and sometimes a small anti vibration extension spring attached to the weight is on one side, large coil thermostatic spring on the other. Some engines have the thermo spring exposed, others such as the engine in this photo have a sheetmetal cover over the spring.

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Ok thanks everyone.

I seem to have nothing on the front side and just a little nub left on the back. I will have to investigate further.

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Here are a couple of photos KenP posted on old threads showing his 37 120 weight and inner heat riser valve construction. Didn't find any good photos showing the spring side but all that side consists of is the large coiled spring. Inner end is inserted in a slot in the riser valve shaft and the spring is wrapped so the outer end is positioned over a stud pressed into the manifold and there is tension on the spring and shaft. As the spring heats, tension is relaxed and the weight drops so the valve opens. There may be a perforated sheetmetal cover held on by a couple of screws and positioned over the spring.

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After removing the manifolds I do find the heat riser flap inside and in the open position. No weights or springs are evident as I'm assuming they were removed and since the flap axle doesn't pivot was specifically left in the open position.

Now back to my original issue. My carb is completely heat soaked and vapor locked after 10 or 15 minutes. Should I make a heat riser block off plate?

Anyone else ever hear off this issue?

Thanks

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I too had a similar issue with my '38 Eight. Not to the extent you have but the fuel in my Carter fuel filter clear glass bulb would be boiling when I checked the engine after shut down. The filter is located a few inches from the carb and over top of the manifolds. Not sure if the carb was "hot" but the filter surely was. My fix, a simple thick sheet metal baffle between the exhaust manifold and the glass filter. I used the head bolts to attach it. Worked perfect. Plus I would think about some insulation around the fuel line in that general area, the type street rods use.

My thoughts are that the carb might be getting hot because hot fuel is entering into it. Since the heat riser is not the issue, I thought too as that was the problem, maybe this baffle and insulation won't hurt. Good luck.