34 PICT 3 preheat?

Our 74 Super has a tube running from the 34 PICT 3 down, and is capped off at the sheet metal. I assume for preheat purposes? I don't know why it got blocked off originally. What did it do, do I need to re-hook it up, or should I remove it completely? If remove completely, can you point me to some blockoff procedures/sources?

If for emissions, I fortunately don't have to have to be sniffed for pollution (74 and earlier exempt here).

Thanks, mck

Reply to
Marion & Victoria Keith
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A metal tube (maybe 1/2" OD)? Runs from near the base of the carb? If so, that used to be the EGR connection to the muffler.

If it's a large diam paper hose from the air cleaner *that* is heated air intake to keep the carb from icing.

Speedy Jim

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Reply to
Speedy Jim

Heat being a concern, and emissions not - what should I do? What is the practical thing?

Thanks, mck

Reply to
Marion & Victoria Keith

Leave it blocked off. Jim

Reply to
Speedy Jim

............When the EGR is working, you actually run leaner and hotter than you would without it. Like Speedy Jim said, block it off.

Reply to
Tim Rogers

You have this backwards. A properly functioning EGR system lowers combustion chamber temperatures, thus reducing the level of oxides of nitrogen(Nox) in the exhaust.

I'm not an engineer, nor do I claim to be one..but I know those VW folks were a smart bunch. If they put it on the car, it was put there for a reason. Hook the thing up.

Chris

Reply to
Hal

..................Yeah, they knew what they were doing. They knew that blending exhaust with the gas/air mixture would result in a leaner and hotter running engine that would have a cleaner exhaust which was needed for emissions testing. Mine is blocked off. They also knew that running a retarded ignition timing at idle would result in lower emissions. I'm running at 7.5 deg BTDC while idling with an SVDA replacement distributor. I'm also getting about 26 to 29 miles to the gallon.

Reply to
Tim Rogers

Tim,

Your logic here is backwards. Introducing exhaust gas that has already been burned will cause the incoming charge to burn COOLER, thus reducing NOX emissions that occur when combustion chamber temperatures are too high.

Most people know this because a typical watercooled car has a passageway for the EGR that over time becomes clogged because of the particulates in the exhaust. In the case of the aircooled VW, there is an EGR filter that is designed to be replaced at specific intervals so as to maintain the functionality of the system. On the newer cars, a clogged EGR passage will either throw a check engine light, or cause you to fail an emissions test because of excessive NOX emissions. Clearing the tube and/or replacing the EGR valve will cure the problem. You may notice that with a failed EGR system the vehicle is more prone to detonation because of the elevated combustion chamber temperatures.

I don't know where you are getting your information about EGR systems making the car run hotter. I've never heard that from anyone, and my own personal experience(plugged EGR passage on my 88 pickup) has proven otherwise as well.

Chris

Reply to
Hal

If your car has the original intake manifold then it has two preheat tubes. They exit from the bottom of the center section of the intake manifold and bolt to the muffler close to the rear facing exhaust ports. Because it has two, the 1974 muffler and intake are one-year only items. It's quite possible that someone installed an earlier intake and muffler because those parts are easier to find if something is damaged. The only other modification necessary is the replacement of the upper two exhaust port studs, and the correct pulley and rear breast tins.

You do NOT want to block off the preheat system, and chances are even if it is not blocked off that the tube is plugged up. You can clear it out with an old clutch cable, you chuck the threaded end into into a drill, and the cut the cable so it is a shade over half the length of the preheat tube. Use the cable as a roto-rooter type tool to clear out the carbon from the tube. If it's plugged, you will probably suffer from intake manifold icing and poor performance. Fixing this will really make your bug drive like a normal car. If it's plugged, you will have performance problems.

I'm not sure which tube exactly you're referring to in your original message, but you mentioned preheat so that's what I'm hoping you were referencing. If not, can you post a picture? The carburetor itself does not have any 'tubes' running from it normally, usually two vaccum lines are about all that attach to the carb(aside from the fuel line and throttle cable). The EGR passage attaches to intake manifold but does not attach to the carburetor.

Chris

Reply to
Hal

Just so we don't get too far afield, the special 2-preheat muffler/ manifold was only used on '74 CALIF models, and only on 4-speed cars.

Man, those designers and inventory folks at VW musta went nuts that year!

Speedy Jim

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Reply to
Speedy Jim

...............I just went back to some resource books and I'm going to have to eat some crow here. Yes, the EGR does lower combustion temperatures but also at the same time reduces power and mileage. I knew there was something wrong with them.........lol

Reply to
Tim Rogers

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