Boiling fuel

That's an unusual description. Fuel should not 'boil' in the carbs. How do you know the fuel is boiling inside the carbs? Is there a particular sound? Or are you describing the condition of a clear fuel filter in the engine bay. Is this 'boiling' going on while the engine is running, or only after it had been running and was sitting for a while. You see, in the later case, 'heat soak' takes place so that components in the upper bay area get hotter than they do when the engine is in the wind.

If you are running dual 44s, then you probably have a big engine. (If you don't have a big engine, the carbs are being wasted and the engine probably runs like crap.) A big engine needs good sealing so that heat doesn't rise up and heat the carbs. So, how is your tin? How are the seals? Got engine lid louvers? Is your engine unusually hot? Are you running an external oil cooler (and filter, of course)? If those carbs really are justified, then you should be pumping it via an electric pump located up front by the tank, with a filter between the tank and the pump.

FWIW, on my 2165 the carbs are cool to the touch even when the rest of the engine is very hot. It is cool because the engine bay is properly ventilated and _sealed_ very well.

My 44mm Webers stay quite cool to the touch even in 95F weather, but I have a very nifty seal, tin and air circulation system. Nyaaa, Nyaaa. :)

My fuel pump is by the tank and pumps a bit uphill. It also has a manual cutoff (and comes off with the ignition switch). When it's cut, the fuel drains back down the line, but the bowl does not empty. All it really does is make you wait another few seconds when you start the engine as the fuel pressure builds again.

Could be. You really have to check them the moment you stop the engine lest heat-soak give you a misreading. As I said, there's no reason they can't run very cool with proper ventilation and sealing.

I think he was referring specifically to boiling *after* the engine shuts off. That's when engine heat soaks into the carb.

I didn't believe my eyes when I first saw fuel gurgling up out of the brass vent tube on a 34PICT. It was after a long run on a really hot day. The engine was always difficult to start after a hot run due to flooding.

Fuel boil?? Can't be, I thought.

I took a kitchen pot and made near-boiling water. Then I took a 34PICT and dunked it in the water. Within seconds, fuel was bubbling and frothing at the vent tube and pouring down into the throat, just as I had seen in the car.

Insulating the carb will have little effect after the engine shuts off. I found it to be marginally helpful while running, as did blocking off the "heat riser" (for the summer only).

Speedy Jim

Spiliotopoulos wrote:>

I was having the same problem with 45drla's; I solved it but cutting down the underhood temperature. I reduced the underhood temp by sealing all the holes in the tinware (including careful fitting of the spark plug rubber flanges), wrapping the header with insulation (there was a HUGE amount of heat coming up through the rear tin), and installing hood stand-offs. These improvements also helped it start a lot easier when it's hot than it used to.

What product did you use to insulate the header? How has the insulation job held up over time?

Tim

Charlie Wils>

Speedy Jim has described the problem properly, a thought i had was to utilise the vents from the fanhousing that go to the heat exchangers to help keep the top half of the engine cooler. I know this would mean that the heating system would be of no use but would it affect anything else? for example the pressure of air being blown to other parts of the engine?

Don't mess with the air cooling system. It was designed to work, and it does. If you don't mind not having a heater, then run a merged header wrapped in carbon-impregnated fiber. Seal everything up good.

That's my tin. :) Got a lot of extra room there. Maybe I should add another engine?

On Tue, 12 Aug 2003 16:10:13 -0500, John Stafford left Mt Vesuvius in a state of jealous awe as he began spewing from the mouth thusly:

All that bright paint and chrome make it go faster? *grin*

-- Travis (Shaggie) '63 VW Camo Baja...

corrodes the vessel that carries it.

Here's the stuff. Get the carbon-impregnated, not the white stuff. (Don't have to paint the carbon.) 1" is much easier to work with and will cover a

1 5/8" merged header up to 4" before the collector.

Wrap:

Stainless fasteners: Tip: start at the exhaust flange, work towards end of pipe. Work slowly. The carbon impregnated stuff is messy - carbon powder does fall out, but harmlessly. Overlap just 1/2 the width, sometimes a little more or less, and when you come to a tight spot, use a screwdriver to gently nudge it open and if you can't, then wrap all around the big part.

I used only nine fasteners, three of them not really neccessary.

Don't remove the hoses from the heater boxes! The pressure in the fanhousing will drop and your cooling will be reduced. Anyway, the carburators are cooling themselves when the engine is running (they suck cool air + the evaporation of fuel absorbs much heat). The problem arises when the engine is turned off, when the carbs are not self-cooled anymore. Then the heat from the exhaust / rear tin heats the inside of the engine compartment and the heat from the heads is conducted to the carbs trough the manifolds.

You can diminish the problem by:

1) Ensuring that the engine is correctly tuned up (correct advance, no lean mixture, valves adjusted) 2) Checking that all seals and factory tin are in place, so that the lower part of the engine is airtight separated from the upper part of the engine. This will also keep out exhaust fumes from the heater in winter months. 3) By using a decklid with vents if you are not allready using. 4) By insulating the exhaust header as the others suggested, or by insulating the lower side of the rear engine tin and approon (this needs extra attention not absorb water cause it may cause your tin to rust from the uderside). 5) By using gaskets of some fiber material between the heads and the manifolds instead of the stock metal ones, to reduce heat transfer from the heads to the manifolds. (Note: Alfa Romeo, in their water-cooled boxer engine equiped with dual carbs (Weber IDFs or Dellortos) used a thick (2-3mm) fiber gasket plus paper gaskets between the carb and the manifold to insulate the carb from the heads, which ran much cooler than our air-cooled heads are). 6) By checking the float adjustment in the carbs. It may be out of adjustment, and the fuel level too high, so that when the fuel boils, it bubbles out of the carb.

You probably won't have the problem with cooler weather, but most of the above suggestions will help your engine running cooler, which is a good thing anyway.

Sorry for the long answer.

Bill, '67 bug.