The Stovebolt Site Forums The Shop Area The HiPo Shop Zenith Carbs boiling over?

On my 261 with cam and 9:1 compression I'm having hot-flooding after shut down problems.

I have a pair of Zenith 228s on a Offy manifold that is heated by tubes from cast Fenton exhaust manifolds. There are 1" heat insulators under the carbs.This has worked well for years but in the past few years I've had hot start problems where the carbs flood the engine. I put in a low-pressure electric fuel pump and everything's fine in moderate temperatures. The repop Carter mechanical had way too much pressure.

So on a recent trip of 4,000 miles, much of it up to 8,000 feet and in hot weather, it floods every time you shut it off. The gas available in high altitude New Mexico, AZ and Utah is 85 octane with 10% ethanol. Back home at 2,400 feet and temps in the 50s there is no problem. But last summer when it was 100 + it would flood but not so bad. I put a pyrometer on it that gave me one more thing to worry about and it says 1200-1300 degrees at 2700RPM under load where it runs most of the time, 2-5" vacuum. Seems hot to me. I'm running 8 deg initial advance and it doesn't ping.When the vacuum comes up and the power valve starts to close, the exh. temp rises. When I'm down to near sea level the temp rises to 1350-1400 at higher vacuum. Foot to the floor it drops down to about 1200 at 0-2" vacuum.

I suppose that manifold heat is contributing but I wonder about the carbs too. Do Zenith 228s have an anti-perculator valve that might be stuck closed? I have had them apart years ago but I don't remember.

Put a "vapor return line" from the carbs back to the tank. You can hook it up using a restrictor in the return line at the source from the carburetors; or wire in a fuel shut-off valve that is opened when the ignition is turned off.

Jon.

Jon:
What part of a 228 do I hook the vapor return line to? I don't remember a fitting other than the fuel inlet. Would the vapor return tee off the fuel inlet to relieve pressure from the fuel pump after shut down? I suspect that the gas in the float bowl is boiling and spilling down into the carb throat. It wasn't convenient to pull the air filter and look on my trip plus being blistering hot. As I'm sure you know a lot of places don't want you working on your rig on their premises. Now that the weather is cool to cold at home it's stopped doing the flooding.

Insert a "tee" at the fuel inlet.

The following from the troubleshooting section of my website:

Jon

A common complaint today is fuel dripping out of the throttle body by the throttle shaft AFTER the engine is switched off. While a number of issues may cause this problem, by far the most common issue is the volatility of modern fuel. Mechanical fuel pumps have a check valve which prevents fuel from moving back to the fuel tank. The problem is as follows:



(1) After the engine is switched off, heat from the engine heats the fuel in the fuel line.

(2) The expanding fuel (increased volatility) creates pressure in the fuel line from the pump to the carburetor.

(3) The check valve prevents the fuel backing up through the fuel pump.

(4) The pressure increases to a point the float/fuel valve combination in the carburetor cannot withstand the pressure.

(5) An amount of fuel (usually from a teaspoon to a couple of tablespoons) flows into the fuel bowl of the carburetor.

(6) This raises the fuel level in the bowl above the main discharge nozzle(s).

(7) Fuel flows through the main discharge nozzle(s) and drips onto the throttle plate(s) which is/are closed, and exits out beside the throttle shaft(s) dripping onto the intake.



Possible solutions:



(1) IF POSSIBLE, AVOID ETHANOL LACED FUEL! Sometimes you can buy real gasoline at a marina

(2) Buy the lowest octane name-brand fuel that does not ping or detonate in your engine (the higher grades often have more ethanol)

(3) Install a “vapor return line” (take a look at return lines used on many factory air-conditioned cars)

(4) Learn to live with the issue.

A phenolic spacer under the carburetor may help, but the return line is the best solution.

Jon

Thanks for the more complete explanation. That all makes sense from what I'm experiencing. I've got phenolic spacers. I think they contribute to carb icing in cold/damp weather but Ive learned to live with that. My did used to insulate the fuel line on his 46Ford to avoid vapor lock. He used aluminum foil and clothes pins.

Old wives tale or whatever. How do wooden clothespins insulate or conduct heat? I've heard that for years and it's nonsense.

Aluminum foil can actually "insulate" a fuel line. It would change the reflectivity of the line and prevent it from picking up radiated heat. It could be significant compared to a flat black fuel line which is the most efficient at gathering radiant heat.

I've heard the clothespin thing for years - clipping wooden clothespins along the fuel line to prevent vapor lock. It serves no purpose.

I think the tin foil does the work of insulating, the clothes pins just hold it on.

But the point of tin foil is that it can be wrapped around and hold itself on. It doesn't need clothes pins.

I've been told by people over the years that just clipping clothes pins to the fuel line alleviates vapor lock. Obviously that's ridiculous but people swear that they've done it, their uncle did it, their grandad did it or whatever.

This tale is right up there with the 80mpg carburetor that GM accidentally let slip out of the factory and then stole it back through subterfuge and locked it away forever.

Lets get back on topic folks.

Heat is a problem here. I had a Studebaker 6 where the fuel pump was right beneath the exhaust manifold and had a factory heat shield. I left that off one time and vapor lock was the result. Here, the problem according to Carb King is that the gas/ethanol is boiling inside the fuel line, or at least expanding more than the needle valves can stand and raising the float level. Any of you Moon shiners remember the boiling point of ethanol at 6,000 feet? The once cad-plated fuel line running between the carbs and above the manifold is now rust colored, so maybe the foil trick will be enough but I'll have to wait till next summer to find out.

Now's the time for checking antifreeze. It frosted hard last night. Goodbye tomato plants.

This is the answer! (IMHO)
My 261 is hard to start after hot soak with e10, with non ethanol turn the key and it's running.

May I ask what electric pump you are using what how you are regulating pressure?

Pump is one I bought at O'Reiliy's when i was broke down on the road. It claims 3.5 psi and I can't remember how many GPH but it seems more than enough. It's replaced a pump with too high a pressure, 6 IIRC. that one had all the usual over-pressure symptoms. This situation is different in that is only does it in hot weather and high altitude after shutdown. No symptoms of leaking needle valve at idle.

If you're going to wrap fuel lines with some sort of an insulating material, there's woven fiberglass tape available intended for motorcycle exhaust pipes that resembles the old standby, asbestos. Even if you manage to find the real stuff, if you use asbestos as insulation, all your kids will be born naked, according to the tree huggers! The fiberglass tape looks just a bit less redneck than tinfoil and clothespins!

www.ebay.com/itm/360492977838?

Jerry

lol

I donno... On my rig there's something to be said for the Redneck Look. Wally Montana posted picture of it as a fuel stop after coming over the Glacier Park pass. Now the paint's faded just enough to give it a patina. Under the hood I've used pipe insulation and tinfoil where the AC low-side hose gets too close to the Exh. manifold. It made a big difference. The AC used to blow warm on long hills. I had to put tinfoil on top because the radiated heat melted the pipe insulation. Now, slightly melted with tinfoil gives just the right look.

On the fuel line, the tinfoil and especially the clothes pins would complete the image. Sometimes I wear striped Oskosh bib overalls but a straw hat won't fit under the cab roof. Maybe a tinfoil hat would do.