Solex carb spacers

[David Jones]

The subject of the Solex phenolic carb spacers came up on another thread so as it was a little off subject my comments are going to be made under a more relevant heading.
Carbs do not run hot and manifolds run considerably cooler than ambient. The phenolic spacers are there to slow the conduction of heat to the carbs but if that is true then why only the 40pii, why not also on the Zenith carbs? I think it may be a performance related reason.
Though the phenolic spacers undoubtedly help to slow the heat transfer to the carbs it does not solve the hard start issue after a hot shutdown so as we are entering the hot part of the driving season it may be apt to put out a reminder.
Plan òn running at a light load for as long as possible before shutting down or let the engine idle for a few minutes to shed some heat. Summer gas starts to boil off the lightest fraction at 95*F and the engine compartment will get way over that on a hot shutdown. Head temps are around 325*F under load.
Park in the shade if possible. If you do a hot start remember that the hot shutdown fuel boil off has sent all those heavy vapors over into the manifold so hold the throttle down when starting to dissipate the over rich mixture and enable the correct mixture for starting.

[C J Murray]

I think it may be a performance related reason.

Thick spacers/gaskets made of various nonmetallic materials are extremely common on many many carbureted engines as originally built. American V8s have them and many motorcycles have them. Many British cars have very thick ones along with heat shields especially when the exhaust ports are nearby.

Certain Weber side draft installations use rubber adapters, springs, and other suspension systems to disassociate the carbs from engine vibration so that the float works correctly. Although our spacers don't have springs they still offer a tiny amount of vibration cushioning.

My guess is that the spacers on 356s give a tiny bit of vibration damping and they slow down the heat transfer in heavy slow traffic and when parked for short periods of time.

Of all of the 356s that I have owned only three ever showed hard starting while hot. One was an engine that had a hot running condition due to various issues. Once they were addressed there were no more hot start problems. The other two were/are both equipped with the old type fuel pumps. Maybe Porsche designed those pumps to create business for dealer service departments? They are very prone to vapor lock due to the orientation of the diaphragm and they require shimming to achieve correct pressure output. Their only benefit today is that they look right on a car that originally had them. Note that Porsche sometimes mounted those pumps with aluminum spacers and sometimes with phenolic spacers. They were obviously trying to address a problem.

Think about the route that fuel takes to get to the carbs. It enters the engine compartment in close proximity to the #3 exhaust port/manifold. It then hugs the top of the 3/4 cylinder head and turns to cross over above the #4 exhaust port/manifold and into the fuel pump which is mounted to an engine case that is at least 180*F. Then it goes to the carbs which are very cool at mid to upper rpm but do get warmer in traffic.

As a mechanic in the early 1970s we saw many vapor lock problems due to the fuel reformulations. We worked on many Datsun Zs and 510s and they had a factory recall to install heat insulation on all the fuel lines.

When my wife and I were dating she had a brand new Dodge Dart Swinger slant six automatic. Driving that car was very dangerous because periodically it would stall when pulling out into traffic from a stop. Scary. When she took her new car to the Dodge dealer they were unable to correct the problem but instead they gave her a free Philadelphia Flyers coffee mug. After she had sold the car I mentioned the problem to George McNichols, my father's favorite Porsche mechanic from our dealer that had become a Chrysler field service rep for the factory. He said that was a common problem because the unleaded fuel attacked the fuel pump diaphragm which swelled and that stopped the fuel flow at idle. So, if you waited for traffic to pass the float bowl would drop level and then when you pressed the gas the engine would quickly run out of fuel, just as cars were bearing down on you.

Install an electric fuel pump for starting and you will never have a fuel related starting problem.

[Brian R Adams]

Park in the shade if possible.

I open the rear deck lid to allow hotter-than-ambient air to rise out of the compartment quickly. If the engine is allowed to cool to ambient for, say, an hour, then restarted before the float bowls have evaporated out, the bowls will refill in a few seconds. If the engine is then immediately shut down, it will not have heated up enough to boil out the fuel.
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[Al Zim]

Many parts of the Porsche engine were direct decedents of the 25 HP VW. This was a necessity since in would put Porsche out of business designing parts that were already working. The Phenolic fuel pump spacer was one of them. As you tightened the fuel pump to the case too much torque would break the plastic part. Then the 36 HP VW engine had been replaced by the 40 HP engine with a direct mount fuel pump. Thus the supply of plastic spacers was coming to and end which it did.

[Brad Ripley]

Are we talking about carb insulator blocks, carb base to manifold or Are we talking about fuel pump insulator blocks, pump to timing cover ?

[Jacques Lefriant]

Hi Brad
i think we are talking about carb base spacers. Al is talking about the spacer that was used on the 2 piece case. even the aluminum(replacement for Al'S) one uses a insulator spacer and the direct mount one also.
j

[David Jones]

The heading for this thread is "Solex carb spacers". Anything else and we are way off track.

[Brian R Adams]

Sad to say, but trolling does occur on this forum. What seems like confusion is sometimes facetiousness.
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[C J Murray]

The heading for this thread is "Solex carb spacers". Anything else and we are way off track.

It is your thread so I can't really argue but I will give it a try anyway.

The thrust of the thread seemed to start focussed on temperature to the carbs and the related problems and how the spacers can help. I was first to mention the fuel pump mounting since the fuel pump mounting onto a hot engine with no rush of intake air is the primary cause of the vapor lock problems, not the carburetors. I then blabbed on about fuel pumps and their mounting which is off topic but if we are concerned about fixing vapor lock is the logical place to focus. Al made the mistake of following my lead.

I'm not sure which aspects of the carb spacers are being discussed.

[Jim Liberty]

Brian A. what is that last word? ........Jim.

[Martin Benade]

“Of or pertaining to” a Facet electric fuel pump? From Websters.

[Jim Liberty]

Martin, this is the second thing I learned this week. The first is that on 1951 Split Window, the starter button is Black. I called the owner out when he came by, telling him it needed to be ivory. I don't embarrass easily, but that did it.........................Jim.

[David Jones]

A comment if I may on vapor locking. Similar to what happens when you open a can of soda. Ambient pressure is lower so entrained gas is released and as gas is sucked from the tank the pressure is lowered so the fuel essentially boils in the line and the pump has difficulty repressurising the fuel into a liquid. Colder fuel will help but it is only a part of the problem.
Look up the ideal gas law and PV constant for the math.
Above a certain pressure a gas becomes a liquid and below that critical pressure it reverts to a gas. Fuel injection is relatively free of vapor locking issues because they have pumps that are submerged in the gas tank and the fuel is under pressure while in transit to the combustion chamber.
There is only so much that can be done to a 356 fuel system but it can work well even in high ambient temps. I have not had any problems with vapor locking on any of my air cooled cars in 60 years.

[Martin Benade]

Jim, the third thing you may have learned this week is not to always trust me. I made that definition up.

[Harlan Halsey]

Dave Merz was selling a nice set of insulating spacers for Zeniths. So everybody can get in on the discussion.